Table of contents

The Schwabe cycle of solar activity exhibits modulations and frequency fluctuations on slow timescales of centuries and millennia. Plausible physical explanations for the cause of these long-term variations of the solar cycle are still elusive, with possible theories including stochasticity of the alpha effect and fluctuations of the differential rotation. It has been suggested recently in the literature that there exists a possible relation between the spatiotemporal structure of the solar cycle and the nonlinear dynamics of magnetohydrodynamic (MHD) Rossby waves at the solar tachocline, including both wave–wave and wave–mean flow interactions. Here we extend the nonlinear theory of MHD Rossby waves presented in a previous article to take into account long-term modulation effects due to a recently discovered mechanism that allows significant energy transfers throughout different wave triads: the precession resonance mechanism. We have found a large number of Rossby–Hauwirtz wave triads whose frequency mismatches are compatible with the solar cycle frequency. Consequently, by analyzing the reduced dynamics of two triads coupled with a single mode (five-wave system), we have demonstrated that in the amplitude regime in which precession resonance occurs, the energy transfer throughout the system yields significant long-term modulations on the main ∼11 yr period associated with intratriad energy exchanges. We further show that such modulations display an inverse relationship between the characteristic wave amplitude and the period of intratriad energy exchanges, which is consistent with the Waldmeier law for the solar cycle. In the presence of a constant forcing and dissipation, the five-wave system in the precession resonance regime exhibits irregular amplitude fluctuations, with some periods resembling the grand minimum states.

The Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP) sounding rocket experiment, launched in 2015 September, observed the hydrogen Lyα line (121.6 nm) in an unprecedented high temporal cadence of 0.3 s. CLASP performed sit-and-stare observations of the quiet Sun near the limb for 5 minutes with a slit perpendicular to the limb and successfully captured an off-limb spicule evolving along the slit. The Lyα line is well suited for investigating how spicules affect the corona because it is sensitive to higher temperatures than other chromospheric lines, owing to its large optical thickness. We found high-frequency oscillations of the Doppler velocity with periods of 20–50 s and low-frequency oscillation of periods of ∼240 s on the spicule. From a wavelet analysis of the time sequence data of the Doppler velocity, in the early phase of the spicule evolution, we found that waves with a period of ∼30 s and a velocity amplitude of 2–3 km s⁻¹ propagated upward along the spicule with a phase velocity of ∼470 km s⁻¹. In contrast, in the later phase, possible downward and standing waves with smaller velocity amplitudes were also observed. The high-frequency waves observed in the early phase of the spicule evolution would be related with the dynamics and the formation of the spicules. Our analysis enabled us to identify the upward, downward, and standing waves along the spicule and to obtain the velocity amplitude of each wave directly from the Doppler velocity for the first time. We evaluated the energy flux by the upward-propagating waves along the spicule, and discussed the impact to the coronal heating.

The ratio between carbon and oxygen is regarded as an important driver of circumstellar and planetary chemistry, which can be used as a parameter to estimate the fractionation among refractory and volatile portions of a planet. From this motivation, nearly 500 stars including some with planets discovered around them are investigated. The relation between the C/O ratio and fractions of icy and refractory species is traced for planetesimals expected to form in their protostellar disks. It is found that low C/O ratios lead to planets rich in ice, but poor in organic and other refractory materials. With increasing C/O ratios, the ice fraction diminishes, where organics increase and other refractory materials dominate. Apart from that, the carbon portion incorporated in the solid phase and the redox state of the environment are altered to analyze their influence on bulk formation for generated planets. Under zero solid carbon contribution, ice formation decreases and refractory formation increases with increasing C/O ratio. When the carbon contribution is considered to be entirely in the solid phase, refractory materials are not significantly affected by the increasing C/O ratio while ice may even disappear. For reducing conditions, the C/O ratio is not an obstacle for ice formation no matter how high it is. Under oxidizing conditions, however, water is not found where the C/O ratio is greater than 0.8. Bulk densities are also calculated according to alternative scenarios along with compositional distributions, and results are compared to solar system objects. This study, therefore, exemplifies how a simple correlation can be drawn between stellar chemistry, redox state, and planetesimal composition.

We present 81 near-infrared (NIR) spectra of 30 Type II supernovae (SNe II) from the Carnegie Supernova Project-II (CSP-II), the largest such data set published to date. We identify a number of NIR features and characterize their evolution over time. The NIR spectroscopic properties of SNe II fall into two distinct groups. This classification is first based on the strength of the He iλ1.083 μm absorption during the plateau phase; SNe II are either significantly above (spectroscopically strong) or below 50 Å (spectroscopically weak) in pseudo equivalent width. However, between the two groups other properties, such as the timing of CO formation and the presence of Sr ii, are also observed. Most surprisingly, the distinct weak and strong NIR spectroscopic classes correspond to SNe II with slow and fast declining light curves, respectively. These two photometric groups match the modern nomenclature of SNe IIP, which show a long duration plateau, and IIL, which have a linear declining light curve. Including NIR spectra previously published, 18 out of 19 SNe II follow this slow declining-spectroscopically weak and fast declining-spectroscopically strong correspondence. This is in apparent contradiction to the recent findings in the optical that slow and fast decliners show a continuous distribution of properties. The weak SNe II show a high-velocity component of helium that may be caused by a thermal excitation from a reverse shock created by the outer ejecta interacting with the red supergiant wind, but the origin of the observed dichotomy is not understood. Further studies are crucial in determining whether the apparent differences in the NIR are due to distinct physical processes or a gap in the current data set.

We characterize the metallicities and physical properties of cool, photoionized gas in a sample of 152 z ≲ 1 strong Lyα forest systems (SLFSs, absorbers with 15 < log N_{H i} < 16.2). The sample is drawn from our Cosmic Origins Spectrograph (COS) circumgalactic medium compendium (CCC), an ultraviolet survey of H i-selected circumgalactic gas around z ≲ 1 galaxies that targets 261 absorbers with 15 < log N_{H i} < 19. We show that the metallicity probability distribution function of the SLFSs at z ≲ 1 is unimodal, skewed to low metallicities with a mean and median of [X/H] = −1.47 and −1.18 dex. Very metal-poor gas with [X/H] < −1.4 represents about half of the population of absorbers with 15 < log N_{H i} ≲ 18, while it is rare at higher N_{H i}. Thus, there are important reservoirs of primitive (though not pristine) diffuse ionized gas around z ≲ 1 galaxies. The photoionized gas around z ≲ 1 galaxies is highly inhomogeneous based on the wide range of metallicities observed (−3 ≲ [X/H] ≲ +0.4) and the fact that there are large metallicity variations (factors of 2 to 25) for most of the closely spaced absorbers (Δv ≲ 300 km s⁻¹) along the same sightlines. These absorbers show a complex evolution with redshift and H i column density, and we identify subtle cosmic evolution effects that affect the interpretation of metallicity distributions and comparison with other absorber samples. We discuss the physical conditions and cosmic baryon and metal budgets of the CCC absorbers. Finally, we compare the CCC results to recent cosmological zoom simulations and explore the origins of the 15 < log N_{H i} < 19 absorbers within the Evolution and Assembly of GaLaxies and their Environments (EAGLE) high-resolution simulations.

Structures in circumstellar disks such as gaps and rings are often attributed to planets. This connection has been difficult to show unequivocally, as other processes may also produce these features. In particular, a photoelectric instability (PEI) has been proposed, operating in gas-rich optically thin disks, that generates structures predicted by planet–disk interactions. We examine the question of how to disentangle the planetary effects on disk structure from the effects of the PEI. We use the Pencil Code to perform 2D global hydrodynamical models of the dynamics of gas and dust in a thin disk with and without planetary perturbers. Photoelectric heating is modeled with an equation of state where pressure is proportional to dust surface density. The drag force on grains and its backreaction on the gas are included. Analyzing the situation without PEI, we find that gas–dust interactions alter the shape of the planetary gap from the dust-free case when the local dust-to-gas ratio ε approaches unity. This result also applies to primordial disks, because dust drifting inward accumulates at the edge of the planetary gap, and any initial dust-to-gas ratio eventually achieves ε = 1 if the dust reservoir is sufficient. We find a result particular to high dust-to-gas ratio disks as well: as dust drifts inward, the dust front becomes a sharp transition, and the backreaction triggers the Rossby wave instability. When PEI is included, we find that it obscures structures induced by planets unless the planet's mass is sufficiently large to carve a noticeable gap. Specifically, the instability generates arcs and rings of regular spacing: a planet is discernible when it carves a dust gap wider than the wavelength of the PEI.

The Sun occasionally undergoes the so-called grand minima, in which its magnetic activity, measured by the number of sunspots, is suppressed for decades. The most prominent grand minima, since the beginning of telescopic observations of sunspots, is called the Maunder minimum (1645–1715), which occurred when the sunspots became rather scarce. The mechanism underlying the grand minima remains poorly understood as there is little observational information of the solar magnetic field at that time. In this study, we examine the records of one candidate aurora display in China and Japan during the Maunder minimum. The presence of auroras in such mid-magnetic latitudes indicates the occurrence of great geomagnetic storms that are usually produced by strong solar flares. However, the records of contemporary sunspot observations from Europe suggest that, at least for the likely aurora event, there was no large sunspot that could produce a strong flare. Through simple theoretical arguments, we show that this geomagnetic storm could have been generated by an eruption giant quiescent filament or a series of such events.

We report high-resolution C, N, Al, Si, and S isotope data of 38 presolar SiC grains of type AB. Seventeen of these grains are of subtype AB1 (¹⁴N/¹⁵N < 440 = solar) and 20 of subtype AB2 (¹⁴N/¹⁵N ≥ 440), previously proposed to be mainly from supernovae (AB1) and J-type carbon stars (AB2), respectively. Our data are compatible with previously obtained isotope data of AB grains, except that ²⁶Al/²⁷Al ratios of AB1 grains span a narrower range. The data are compared with predictions from supernova models that consider H ingestion into the He shell during the pre-supernova phase. In these models a mixture of explosive H and He burning occurs at the bottom of the He shell during passage of the supernova shock, forming the so-called O/nova zone. Mixing matter from the O/nova zone with matter from the overlying He/C zone and the stellar envelope shows that the isotopic compositions and trends of both AB1 and AB2 grains can be matched within the model uncertainties. This demonstrates that supernovae should be considered as potential sources of AB2 grains, in addition to J-type carbon stars and born-again asymptotic giant branch stars, as previously proposed.

Constraining parameters such as the initial mass function high-mass slope and the frequency of Type Ia supernovae is of critical importance in the ongoing quest to understand galactic physics and create realistic hydrodynamical simulations. In this paper, we demonstrate a method for precisely determining these using individual chemical abundances from a large set of stars, coupled with some estimate of their ages. Inference is performed via the simple chemical evolution model Chempy in a Bayesian framework, marginalizing over each star's specific interstellar medium parameters, including an element-specific "model error" parameter to account for inadequacies in our model. Hamiltonian Monte Carlo methods are used to sample the posterior function, which is made possible by replacing Chempy with a trained neural network at negligible error. The approach is tested using data from both Chempy and the IllustrisTNG simulation, showing subpercent agreement between inferred and true parameters using data from up to 1600 individual stellar abundances. For IllustrisTNG, the strongest constraints are obtained from metal ratios, competitive with those from other methods including star counts. Analysis using a different set of nucleosynthetic yields shows that incorrectly assumed yield models can give non-negligible bias in the derived parameters; this is reduced by our model errors, which further show how well the yield tables match the data. We also find a significant bias from analyzing only a small set of stars, as is often done in current analyses. The method can be easily applied to observational data, giving tight bounds on key galactic parameters from chemical abundances alone.

Using 145 early- and late-type galaxies (ETGs and LTGs) with directly measured supermassive black hole masses, M_BH, we build upon our previous discoveries that: (i) LTGs, most of which have been alleged to contain a pseudobulge, follow the relation ${M}_{\mathrm{BH}}\propto {M}_{* ,\mathrm{sph}}^{2.16\pm 0.32}$; and (ii) the ETG relation ${M}_{\mathrm{BH}}\propto {M}_{* ,\mathrm{sph}}^{1.27\pm 0.07}$ is an artifact of ETGs with/without disks following parallel ${M}_{\mathrm{BH}}\propto {M}_{* ,\mathrm{sph}}^{1.9\pm 0.2}$ relations that are offset by an order of magnitude in the M_BH direction. Here, we searched for substructure in the diagram of M_BH versus central velocity dispersion σ, using our recently published multi-component galaxy decompositions, by investigating divisions based on the presence of a depleted stellar core (major dry merger), a disk (minor wet/dry merger, gas accretion), or a bar (evolved unstable disk). The Sérsic and core-Sérsic galaxies define two distinct relations: ${M}_{\mathrm{BH}}\propto {\sigma }^{5.75\pm 0.34}$ and ${M}_{\mathrm{BH}}\propto {\sigma }^{8.64\pm 1.10}$, with ${{\rm{\Delta }}}_{\mathrm{rms}| \mathrm{BH}}=0.55$ and 0.46 dex, respectively. We also report on the consistency with the slopes and bends in the galaxy luminosity (L)–σ relation due to Sérsic and core-Sérsic ETGs, and LTGs that all have Sérsic light profiles. Two distinct relations (superficially) reappear in the M_BH–σ diagram upon separating galaxies with/without a disk (primarily for the ETG sample), while we find no significant offset between barred and non-barred galaxies, nor between galaxies with/without active galactic nuclei. We also address selection biases purported to affect the scaling relations for dynamically measured M_BH samples. Our new M_BH–σ relations, dependent on morphological type, more precisely estimate M_BH in other galaxies, and hold implications for galaxy/black hole coevolution theories, simulations, feedback, the pursuit of a black-hole fundamental plane, and calibration of virial f-factors for reverberation mapping.

Lead (Pb) is predominantly produced by the slow neutron-capture process (s process) in asymptotic giant branch (AGB) stars. In contrast to significantly enhanced Pb abundances predicted by low-mass, low-metallicity AGB models, observations of Magellanic post-AGB stars show incompatibly low Pb abundances. Observations of carbon-enhanced metal-poor (CEMP) stars whose s-process enrichments are accompanied by heavy elements traditionally associated with the rapid neutron-capture process (r process) have raised the need for a neutron-capture process operating at neutron densities intermediate to the s and r process: the so-called i process. We study i-process nucleosynthesis with single-zone nuclear-network calculations. Our i-process models can explain the heavy-element abundance patterns measured in Magellanic post-AGB stars including their puzzlingly low Pb abundances. Furthermore, the heavy-element enhancements in the post-AGB and CEMP-i stars, particularly their Pb abundance, allow us to characterize the neutron densities and exposures of the i process that produced the observed abundance patterns. We find that the lower-metallicity CEMP-i stars ($\left[\mathrm{Fe}/{\rm{H}}\right]\approx -2.5$) have heavy-element abundances best matched by models with higher neutron densities and exposures (τ > 2.0 mbarn⁻¹) compared to the higher-metallicity post-AGB stars ($\left[\mathrm{Fe}/{\rm{H}}\right]\approx -1.3$, τ < 1.3 mbarn⁻¹). This offers new constraints and insights regarding the properties of i-process sites and demonstrates that the responsible process operates on timescales of the order of a few years or less.

Carbon-deficient red giants (CDRGs) are a rare class of peculiar red giants, also called "weak G-band" or "weak CH" stars. Their atmospheric compositions show depleted carbon, a low ${}^{12}{\rm{C}}{/}^{13}{\rm{C}}$ isotopic ratio, and an overabundance of nitrogen, indicating that the material at the surface has undergone CN-cycle hydrogen burning. I present Strömgren uvby photometry of nearly all known CDRGs. Barium stars, having an enhanced carbon abundance, exhibit the "Bond–Neff effect"—a broad depression in their energy distributions at ∼4000 Å, recently confirmed to be due to the CH molecule. This gives Ba ii stars unusually low Strömgren c₁ photometric indices. I show that CDRGs, lacking CH absorption, exhibit an "anti-Bond–Neff effect"—higher c₁ indices than normal red giants. Using precise parallaxes from Gaia DR2, I plot CDRGs in the color–magnitude diagram (CMD) and compare them with theoretical evolution tracks. Most CDRGs lie in a fairly tight clump in the CMD, indicating initial masses in the range ∼2–$3.5\,{M}_{\odot }$, if they have evolved as single stars. It is unclear whether they are stars that have just reached the base of the red-giant branch and the first dredge-up of CN-processed material, or are more highly evolved helium-burning stars in the red-giant clump. About 10% of CDRGs have higher masses of ∼4–$4.5\,{M}_{\odot }$, and exhibit unusually high rotational velocities. I show that CDRGs lie at systematically larger distances from the Galactic plane than normal giants, possibly indicating a role of binary mass transfer and mergers. CDRGs continue to present a major puzzle for our understanding of stellar evolution.

Long duration gamma-ray bursts may serve as standard candles to constrain cosmological parameters by probing the Hubble diagram well beyond the range of redshift currently accessible using SNe Ia. The standardization of gamma-ray bursts (GRBs) is based on phenomenological relations between two or more parameters found from spectral modeling, one of which is strongly dependent on the cosmological model. The Amati relation links the source-frame energy ${E}_{{\rm{i}},{\rm{p}}}$ at which the prompt gamma-ray spectral energy distribution νF_ν peaks, and the isotropic-equivalent bolometric energy ${E}_{\mathrm{iso}}$ emitted during the prompt phase. We performed spectral analysis of 26 GRBs with known redshift that have been detected by the Fermi-Large Area Telescope (LAT) during its nine years of operations from 2008 July to 2017 September, thus extending the computation of E_iso to the 100 MeV range. Multiple components are required to fit the spectra of a number of GRBs. We found that the Amati relation is satisfied by the 25 LGRBs, with best-fit parameters similar to previous studies that used data from different satellite experiments, while the only short GRB with known redshift is an outlier. Using the Amati relation, we extend the Hubble diagram to redshift 4.35 and constrain the Hubble constant and dark-energy density in the ΛCDM model, with Fermi-LAT GRBs alone and together with another sample of 94 GRBs and with the latest Supernovae type-Ia data. Our results are consistent with the currently acceptable ranges of those cosmological parameters within errors.

We present lifetime measurements using beam-foil techniques for radiative transitions from the 3p⁴(¹S)4s²S_1/2, 3p⁴(³P)5 ${s}^{2}{P}_{1/\mathrm{2,3}/2}$, and 3p⁴(³P)3d²F_5/2 levels in Cl I and the corresponding results of the oscillator strengths for transitions at 1004.68, 1079.88, 1090.73, and 1094.77 Å, respectively. We compare our experimental results with available theoretical calculations and astronomical observations in an effort to resolve discrepancies among them.

We report a spectroscopic identification of two new changing-look active galactic nuclei (CL-AGNs): SDSS J104705.16+544405.8 and SDSS J120447.91+170256.8, both with a "turn-off" type transition from type-1 to type-1.8/1.9. The identification is arrived at through a follow-up spectroscopic observation of the five CL-AGNs candidates that are extracted from the sample recently released in Macleod et al. The candidates are extracted by the authors from the Sloan Digit Sky Survey Data Release 7, and are spectroscopically confirmed quasars with large amplitude variability. By compiling a sample of 26 previously identified CL-AGNs, we confirm the claim by Macleod et al. that CL-AGNs tend to be biased against a low Eddington ratio, and identify an overlap between the CL-AGNs at their dim state and the so-called intermediate-type AGNs. The overlap implies that there two populations of the intermediate-type AGNs with different origins. One is due to the torus orientation effect, and the other to the intrinsic change of the accretion rate of the central supermassive black holes.

Observations with the Wisconsin ${\rm{H}}\alpha$ Mapper reveal a large, diffuse ionized halo that surrounds the Small Magellanic Cloud (SMC). We present the first kinematic ${\rm{H}}\alpha$ survey of an extended region around the galaxy, from $({\ell },b)=(289\buildrel{\circ}\over{.} 5,-35\buildrel{\circ}\over{.} 0)$ to $(315\buildrel{\circ}\over{.} 1,-5\buildrel{\circ}\over{.} 3)$ and covering $+90\leqslant {v}_{\mathrm{LSR}}\leqslant +210\ \mathrm{km}\,{{\rm{s}}}^{-1}$. The ionized gas emission extends far beyond the central stellar component of the galaxy, reaching similar distances to that of the diffuse neutral halo traced by 21 cm observations. ${\rm{H}}\alpha$ emission extends several degrees beyond the sensitivity of current H i surveys toward smaller galactic longitudes and more negative galactic latitudes. The velocity field of the ionized gas near the SMC appears similar to the neutral halo of the galaxy. Using the observed emission measure as a guide, we estimate the mass of this newly revealed ionized component to be roughly $(0.8\mbox{--}1.0)\times {10}^{9}\,{M}_{\odot }$, which is comparable to the total neutral mass in the same region of $(0.9\mbox{--}1.1)\times {10}^{9}\,{M}_{\odot }$. We find ratios of the total ionized gas mass divided by the total neutral plus ionized gas mass in three distinct subregions to be: (1) 46%–54% throughout the SMC and its extended halo, (2) 12%–32% in the SMC Tail that extends toward the Magellanic Bridge, and (3) 65%–79% in a filament that extends away from the SMC toward the Magellanic Stream. This newly discovered, coherent ${\rm{H}}\alpha$ filament does not appear to have a well-structured neutral component and is also not coincident with two previously identified filaments traced by 21 cm emission within the Stream.

We investigate a conceptual modification of the halo occupation distribution approach, using the halos' present-day maximal circular velocity, V_max, as an alternative to halo mass. In particular, using a semianalytic galaxy formation model applied to the Millennium WMAP7 simulation, we explore the extent that switching to V_max as the primary halo property incorporates the effects of assembly bias into the formalism. We consider fixed number density galaxy samples ranked by stellar mass and examine the variations in the halo occupation functions with either halo concentration or formation time. We find that using V_max results in a significant reduction in the occupancy variation of the central galaxies, particularly for concentration. The satellites' occupancy variation on the other hand increases in all cases. We find effectively no change in the halo clustering dependence on concentration, for fixed bins of V_max compared to fixed halo mass. Most crucially, we calculate the impact of assembly bias on galaxy clustering by comparing the amplitude of clustering to that of a shuffled galaxy sample, finding that the level of galaxy assembly bias remains largely unchanged. Our results suggest that while using V_max as a proxy for halo mass diminishes some of the occupancy variations exhibited in the galaxy–halo relation, it is not able to encapsulate the effects of assembly bias potentially present in galaxy clustering. The use of other more complex halo properties, such as V_peak, the peak value of V_max over the assembly history, provides some improvement and warrants further investigation.

Approximately one-third of the gamma-ray sources in the third Fermi-LAT catalog are unidentified or unassociated with objects at other wavelengths. Observations with the X-Ray Telescope on the Neil Gehrels Swift Observatory (Swift-XRT) have yielded possible counterparts in ∼30% of these source regions. The objective of this work is to identify the nature of these possible counterparts, utilizing their gamma-ray properties coupled with the Swift derived X-ray properties. The majority of the known sources in the Fermi catalogs are blazars, which constitute the bulk of the extragalactic gamma-ray source population. The galactic population on the other hand is dominated by pulsars. Overall, these two categories constitute the majority of all gamma-ray objects. Blazars and pulsars occupy different parameter space when X-ray fluxes are compared with various gamma-ray properties. In this work, we utilize the X-ray observations performed with the Swift-XRT for the unknown Fermi sources and compare their X-ray and gamma-ray properties to differentiate between the two source classes. We employ two machine-learning algorithms, decision tree and random forest (RF) classifier, to our high signal-to-noise ratio sample of 217 sources, each of which corresponds to Fermi unassociated regions. The accuracy scores for both methods were found to be 97% and 99%, respectively. The RF classifier, which is based on the application of a multitude of decision trees, associated a probability value (P_bzr) for each source to be a blazar. This yielded 173 blazar candidates from this source sample, with P_bzr ≥ 90% for each of these sources, and 134 of these possible blazar source associations had P_bzr ≥ 99%. The results yielded 13 sources with P_bzr ≤ 10%, which we deemed as reasonable candidates for pulsars, seven of which result with P_bzr ≤ 1%. There were 31 sources that exhibited intermediate probabilities and were termed ambiguous due to their unclear characterization as a pulsar or a blazar.

We report the discovery of a young ($\tau \sim 117\,{\rm{Myr}}$), low-mass ($M\sim 1200\,{M}_{\odot }$), metal-poor ($[{\rm{Fe}}/{\rm{H}}]\sim -1.14$) stellar association at a heliocentric distance $D\approx 28.7\,{\rm{kpc}}$, placing it far into the Milky Way (MW) halo. At its present Galactocentric position $(R,z)\sim (23,15)\,{\rm{kpc}}$, the association is (on the sky) near the leading arm of the gas stream emanating from the Magellanic Cloud system, but is located $\approx 60^\circ$ from the Large Magellanic Cloud center on the other side of the MW disk. If the cluster is colocated with H i gas in the stream, we directly measure the distance to the leading arm of the Magellanic stream. The measured distance is inconsistent with Magellanic stream model predictions that do not account for ram pressure and gas interaction with the MW disk. The estimated age of the cluster is consistent with the time of last passage of the leading arm gas through the Galactic midplane; we therefore speculate that this star formation event was triggered by its last disk midplane passage. Most details of this idea remain a puzzle: the Magellanic stream has low column density, the MW disk at large radii has low gas density, and the relative velocity of the leading arm and MW gas is large. However it formed, the discovery of a young stellar cluster in the MW halo presents an interesting opportunity for study. This cluster was discovered with Gaia astrometry and photometry alone, but follow-up DECam photometry was crucial for measuring its properties.

We have compiled the most complete census of high-mass X-ray binaries (HMXBs) in the Small Magellanic Cloud with the aim to investigate the formation efficiency of young accreting binaries in its low-metallicity environment. In total, we use 123 X-ray sources with detections in our Chandra X-ray Visionary Program (XVP), supplemented by 14 additional (likely and confirmed) HMXBs identified by Haberl & Sturm that fall within the XVP area, but are neither detected in our survey (nine sources) nor matched with any of the 127 sources identified in the XVP data (five sources). Specifically, we examine the number ratio of the HMXBs [N(HMXBs)] to (a) the number of OB stars, (b) the local star formation rate (SFR), and (c) the stellar mass produced during the specific star formation burst, all as a function of the age of their parent stellar populations. Each of these indicators serves a different role, but in all cases we find that the HMXB formation efficiency increases as a function of time (following a burst of star formation) up to ∼40–60 Myr, and then gradually decreases. The formation efficiency peaks at ∼30–40 Myr with average rates of ${\text{}}{\rm{N}}(\mathrm{HMXB})/\mathrm{SFR}={339}_{-83}^{+78}$${({M}_{\odot }/\mathrm{yr})}^{-1}$, and N(HMXB)/M$\star =({8.74}_{-0.92}^{+1.0})\times {10}^{-6}\,{M}_{\odot }^{-1}$, in good agreement with previous estimates of the average formation efficiency in the broad ∼20–60 Myr age range.

Compact, continuously launched jets in black hole X-ray binaries (BHXBs) produce radio to optical/IR synchrotron emission. In most BHXBs, an IR excess (above the disk component) is observed when the jet is present in the hard spectral state. We investigate why some BHXBs have prominent IR excesses and some do not, quantified by the amplitude of the IR quenching or recovery over the transition from/to the hard state. We find that the amplitude of the IR excess can be explained by inclination-dependent beaming of the jet synchrotron emission and the projected area of the accretion disk. Furthermore, we see no correlation between the expected and the observed IR excess for Lorentz factor 1, which is strongly supportive of relativistic beaming of the IR emission, confirming that the IR excess is produced by synchrotron emission in a relativistic outflow. Using the amplitude of the jet fade and recovery over state transitions and the known orbital parameters, we constrain for the first time the bulk Lorentz factor range of compact jets in several BHXBs (with all the well-constrained Lorentz factors lying in the range of Γ = 1.3–3.5). Under the assumption that the Lorentz factor distribution of BHXB jets is a power law, we find that $N({\rm{\Gamma }})\propto {{\rm{\Gamma }}}^{-{1.88}_{-0.34}^{+0.27}}$. We also find that the very high amplitude IR fade/recovery seen repeatedly in the BHXB GX 339–4 favors a low inclination angle ($\lesssim 15^\circ$) of the jet.

The Milky Way is a unique laboratory in which stellar properties can be measured and analyzed in detail. In particular, stars in the older populations encode information on the mechanisms that led to the formation of our Galaxy. In this article, we analyze the kinematics, spatial distribution, and chemistry of a large number of stars in the solar neighborhood, where all of the main Galactic components are well represented. We find that the thick disk comprises two distinct and overlapping stellar populations with different kinematic properties and chemical compositions. The metal-weak thick disk (MWTD) contains two-times less metal content than the canonical thick disk, and exhibits enrichment of light elements typical of the oldest stellar populations of the Galaxy. The rotational velocity of the MWTD around the Galactic center is ∼150 km s⁻¹, corresponding to a rotational lag of 30 km s⁻¹ relative to the canonical thick disk (∼180 km s⁻¹), with a velocity dispersion of 60 km s⁻¹. This stellar population likely originated from the merger of a dwarf galaxy during the early phases of our Galaxy's assembly, or it is a precursor disk, formed in the inner Galaxy and brought into the solar neighborhood by bar instability or spiral-arm formation mechanisms.

The Chandra Deep Field (CDF)-S is the deepest X-ray image available and will remain so for the near future. We provide a spectroscopic (64.5%; 64% with spectral classifications) and photometric redshift catalog for the full 7 Ms sample, but much of our analysis focuses on the central (off-axis angles <57) region, which contains a large, faint ALMA sample of 75 > 4.5σ 850 μm sources. We measure the 850 μm fluxes at the X-ray positions using the ALMA images, where available, or an ultradeep SCUBA-2 map. We find that the full X-ray sample produces ∼10% of the 850 μm extragalactic background light. We separate the submillimeter-detected X-ray sources into star-forming galaxies and active galactic nuclei (AGNs) using a star formation rate (SFR) versus X-ray luminosity calibration for high-SFR galaxies. We confirm this separation using the X-ray photon indices. We measure the X-ray fluxes at the accurate positions of the 75 ALMA sources and detect 70% at >3σ in either the 0.5–2 or 2–7 keV bands. However, many of these may produce both their X-ray and submillimeter emission by star formation. Indeed, we find that only 20% of the ALMA sources have intermediate X-ray luminosities (rest-frame 8–28 keV luminosities of 10^42.5–10⁴⁴ erg s⁻¹), and none has a high X-ray luminosity (>10⁴⁴ erg s⁻¹). Conversely, after combining the CDF-S with the CDF-N, we find extreme star formation (SFR > 300 M_⊙ yr⁻¹) in some intermediate X-ray luminosity sources but not in any high X-ray luminosity sources. We argue that the quenching of star formation in the most luminous AGNs may be a consequence of the clearing of gas in these sources.

We present ALMA observations of the CO(1−0) line and 3 mm continuum emission in eight ultraluminous infrared (IR) quasi-stellar objects (QSOs) at z = 0.06–0.19. All eight IR QSO hosts are clearly resolved in their CO molecular gas emission with a median source size of 3.2 kpc, and seven out of eight sources are detected in 3 mm continuum, which is found to be more centrally concentrated with respect to molecular gas with sizes of 0.4−1.0 kpc. Our observations reveal a diversity of CO morphology and kinematics for the IR QSO systems, which can be roughly classified into three categories: rotating gas disk with ordered velocity gradient, compact CO peak with disturbed velocity, and multiple CO distinct sources undergoing a merger between a luminous QSO and a companion galaxy separated by a few kpc. The molecular gas in three of the IR QSO hosts is found to be rotation-dominated with a ratio of the maximum rotation velocity to the local velocity dispersion of V_rot/σ = 4–6. Basic estimates of the dynamical masses within the CO-emitting regions give masses between 7.4 × 10⁹ and 6.9 × 10¹⁰M_⊙. We find an increasing trend between black hole mass accretion rate and star formation rate (SFR) over 3 orders of magnitude in far-IR luminosity/SFR, in line with the correlation between QSO bolometric luminosity and star formation activity, indicative of a likely direct connection between active galactic nuclei and star formation activity over galaxy evolution timescales.

We demonstrate the ability of convolutional neural networks (CNNs) to mitigate systematics in the virial scaling relation and produce dynamical mass estimates of galaxy clusters with remarkably low bias and scatter. We present two models, CNN_1D and CNN_2D, which leverage this deep learning tool to infer cluster masses from distributions of member galaxy dynamics. Our first model, CNN_1D, infers cluster mass directly from the distribution of member galaxy line-of-sight velocities. Our second model, CNN_2D, extends the input space of CNN_1D to learn on the joint distribution of galaxy line-of-sight velocities and projected radial distances. We train each model as a regression over cluster mass using a labeled catalog of realistic mock cluster observations generated from the MultiDark simulation and UniverseMachine catalog. We then evaluate the performance of each model on an independent set of mock observations selected from the same simulated catalog. The CNN models produce cluster mass predictions with lognormal residuals of scatter as low as 0.132 dex, greater than a factor of 2 improvement over the classical M–σ power-law estimator. Furthermore, the CNN model reduces prediction scatter relative to similar machine-learning approaches by up to 17% while executing in drastically shorter training and evaluation times (by a factor of 30) and producing considerably more robust mass predictions (improving prediction stability under variations in galaxy sampling rate by 30%).

We present a numerical study of the interactions between the elongated active galactic nuclei outflows representing an evolved, narrow-angle tail (NAT) radio galaxy and planar, transverse ICM shock fronts characteristic of those induced by galaxy cluster mergers (incident Mach numbers 2–4). The simulated NAT formation was reported previously in O'Neill et al. Our simulations utilize a three-dimensional, Eulerian magnetohydrodynamic code along with energy-dependent Eulerian transport of passive cosmic ray electrons. Our analysis of the shock/NAT interaction applies a Riemann problem-based theoretical model to interpret complex shock front behavior during passage through the highly heterogeneous structures of the simulated NAT tails. In addition to shock compression, shock-induced vortical motions are observed within the tails that contribute to coherent turbulent dynamo processes that continue to amplify the magnetic fields in the tails well after initial shock compression. We analyze synthetic radio observations spanning the NAT-shock interaction period, and examine the brightness, spectral and polarization properties of our shock-rejuvenated radio tails, as well as the extent to which the pre-shock states of the plasma and particle populations in our tails influence post-shock observations. Finally, we evaluate our findings in the possible context of a physical analogy to our simulated NAT providing the precursor to a cluster "radio relic" associated with an impacting ICM shock.

In situ experiments from the Apollo missions confirmed the presence of a tenuous exosphere on the Moon comprised of atoms and light molecular species. Of the most prominent volatiles found in the exosphere, molecular hydrogen (H₂) has drawn considerable attention because the confirmed detection of surface water has led many scientists to believe that proton bombardment of silicate minerals from the solar wind is the mechanism by which this water forms. As molecular hydrogen formation is a competing mechanism to bound OH/H₂O in the regolith, experimental studies are needed to determine the efficiency of molecular hydrogen formation from the solar wind. Here we show that, under simulated lunar conditions, the formation, storage, and release of molecular deuterium—as a proxy of molecular hydrogen—from deuteron implanted olivine is facile. Secondary ion mass spectrometry results reveal that diffusion processes also enrich grains with deuterium at depths beyond the maximum penetration depth of the incident ions close to 100 nm. In addition, the maximum yield of molecular deuterium escaping the amorphous rims under simulated lunar conditions strongly supports previous studies, which claim that the solar wind represents the dominant source of exospheric molecular hydrogen.

Pre–Big Bang models in string cosmology predict a relic background of gravitational wave radiation in the early universe. The spectrum of this background shows that the energy density rises rapidly with frequency, which is an interesting target for high-frequency (i.e., kilohertz) detectors. In this paper, we discussed the constraining power of multiple configurations of current and future gravitational wave detector (GWD) networks to the stochastic background predicted in string cosmology. The constraining power is jointly determined by the overlap reduction function and the sensitivity curves of multiple detectors. And we further elaborated on the possible contribution of a future Chinese detector and a kilohertz detector to the constraining power of detector network for stochastic background in string cosmology. Our results show that the detectability of the GWD network for the string cosmology gravitational wave background will improve considerably with the joining of a Chinese detector. This is because a Chinese detector (e.g., located at Wuhan), together with KAGRA, has a better overlap reduction function than the laser interferometer gravitational wave observatory detector pair, and therefore lead to more stringent limits for stochastic background detection. And with ideal overlap reduction function, namely, colocated detectors, a kilohertz sensitivity curve has better performance than previous detectors for stochastic background detection. Finally, the results are compared with the limitations given by the observational constraint of the Big Bang nucleosynthesis bound.

The energy balance and climate of planets can be affected by the reflective properties of their land, ocean, and frozen surfaces. Here we investigate the effect of host star spectral energy distribution (SED) on the albedo of these surfaces using a one-dimensional energy balance model. Incorporating spectra of M-, K-, G-, and F-dwarf stars, we determined the effect of varying fractional and latitudinal distribution of land and ocean surfaces as a function of host star SED on the overall planetary albedo, climate, and ice-albedo feedback response. While noting that the spatial distribution of land masses on a given planet will have an effect on the overall planetary energy balance, we find that terrestrial planets with higher average land/ocean fractions are relatively cooler and have higher albedo regardless of star type. For Earth-like planets orbiting M-dwarf stars, the increased absorption of water ice in the near-infrared, where M-dwarf stars emit much of their energy, resulted in warmer global mean surface temperatures, ice lines at higher latitudes, and increased climate stability as the ice-albedo feedback became negative at high land fractions. Conversely, planets covered largely by ocean, and especially those orbiting bright stars, had a considerably different energy balance due to the contrast between the reflective land and the absorptive ocean surface, which in turn resulted in warmer average surface temperatures than land-covered planets and a stronger potential ice-albedo feedback. While dependent on the properties of individual planetary systems, our results place some constraints on a range of climate states of terrestrial exoplanets based on albedo and incident flux.

We report the quasi-simultaneous INTEGRAL, SWIFT, and NuSTAR observations showing spectral state transitions in the neutron star low-mass X-ray binary 1RXS J180408.9−342058 during its 2015 outburst. We present results of the analysis of high-quality broad energy band (0.8–200 keV) data in three different spectral states: high/soft, low/very-hard, and transitional state. The broadband spectra can be described in general as the sum of thermal Comptonization and reflection due to illumination of an optically thick accretion disk. During the high/soft state, blackbody emission is generated from the accretion disk and the surface of the neutron star. This emission, measured at a temperature of kT_bb ∼ 1.2 keV, is then Comptonized by a thick corona with an electron temperature of ∼2.5 keV. For the transitional and low/very-hard state, the spectra are successfully explained with emission from a double Comptonizing corona. The first component is described by thermal Comptonization of seed disk/neutron star photons (kT_bb ∼ 1.2 keV) by a cold corona cloud with kT_e ∼ 8–10 keV, while the second one originates from lower temperature blackbody photons (kT_bb ≤ 0.1 keV) Comptonized by a hot corona (kT_e ∼ 35 keV). Finally, from NuSTAR observations, there is evidence that the source is a new clocked burster. The average time between two successive X-ray bursts corresponds to ∼7.9 and ∼4.0 ks when the persistent emission decreases by a factor of ∼2, moving from a very hard to transitional state. The accretion rate ($\sim 4\times {10}^{-9}\,{M}_{\odot }\,{\mathrm{yr}}^{-1}$) and the decay time of the X-ray bursts longer than ∼30 s suggest that the thermonuclear emission is due to mixed H/He burning triggered by thermally unstable He ignition.

We present deep Chandra observations of A3411–12, a remarkable merging cluster that hosts the most compelling evidence for electron reacceleration at cluster shocks to date. Using the ${Y}_{{\rm{X}}}\mbox{--}M$ scaling relation, we find r₅₀₀ ∼ 1.3 Mpc, ${M}_{500}=(7.1\pm 0.7)\times {10}^{14}\ {M}_{\odot }$, ${kT}=6.5\pm 0.1\,\mathrm{keV}$, and a gas mass of ${M}_{{\rm{g}},500}=(9.7\pm 0.1)\times {10}^{13}{M}_{\odot }$. The gas mass fraction within r₅₀₀ is ${f}_{{\rm{g}}}=0.14\pm 0.01$. We compute the shock strength using density jumps to conclude that the Mach number of the merging subcluster is small ($M\leqslant {1.15}_{-0.09}^{+0.14}$). We also present density, temperature, pseudo-pressure, and pseudo-entropy maps. Based on the pseudo-entropy map, we conclude that the cluster is undergoing a mild merger, consistent with the small Mach number. On the other hand, radio relics extend over Mpc scale in the A3411–12 system, which strongly suggests that a population of energetic electrons already existed over extended regions of the cluster.

The NuSTAR Legacy program titled Unidentified INTEGRAL Sources targeted faint hard X-ray sources revealed by INTEGRAL in the Galactic plane in order to provide conclusive identification of their nature and insights on the population of faint hard X-ray sources. The NuSTAR and Swift X-Ray Telescope observations obtained in 2015–2017 contributed to the successful identification of five persistent sources. Here, we report on the spectral and variability analyses that helped to consolidate the classifications of IGR J10447–6027, IGR J16181–5407, and IGR J20569+4940 as active galactic nuclei and IGR J17402–3656 as an intermediate polar. An optical spectrum of the blazar IGR J20569+4940 is also presented. Combining these results with successful identifications of other such faint and persistent INTEGRAL sources reported in the literature, we investigate possible implications for the population of persistent high-mass X-ray binaries (HMXBs) below the identification completion limit of the INTEGRAL survey. The current trend hints at a deficit of persistent HMXBs below F_{17–60 keV} = 10⁻¹¹ erg cm⁻² s⁻¹, but additional efforts dedicated to classifying faint hard X-ray sources are needed before we can draw solid conclusions.

A hyperbolic cell-centered finite volume solver (HCCFVS) is proposed to obtain the potential magnetic field solutions prescribed by the solar observed magnetograms. By introducing solution gradients as additional unknowns and adding a pseudo-time derivative, HCCFVS transforms the second-order Poisson equation into an equivalent first-order pseudo-time-dependent hyperbolic system. Thus, instead of directly solving the Poisson equation, HCCFVS obtains the solution to the Poisson equation by achieving the steady-state solution to this first-order hyperbolic system. The code is established in Fortran 90 with Message Passing Interface parallelization. To preliminarily demonstrate the effectiveness and accuracy of the code, two test cases with exact solutions are first performed. The numerical results show its second-order convergence. Then, the code is applied to numerically solve the solar potential magnetic field problem. The solutions demonstrate the capability of HCCFVS to adequately handle the solar potential field problem, and thus it can provide a promising method of solving the same problem, except for the spherical harmonic expansion and the iterative finite difference method. Finally, by using the potential magnetic fields from HCCFVS and the spherical harmonic expansion as initial inputs, we make a comparative study on the steady-state solar corona in Carrington rotation 2098 to reaffirm the HCCFVS's performance. Both simulations show that their modeled results are similar and capture the large-scale solar coronal structures. The average relative divergence errors, controlled by solving the Poisson equation in the projection method with HCCFVS for both simulations, are kept at an acceptable level.

Transit spectroscopy of terrestrial planets around nearby M dwarfs will be a primary goal of space missions in coming decades. Three-dimensional climate modeling has shown that slow-synchronous rotating terrestrial planets may develop thick clouds at the substellar point, increasing the albedo. For M dwarfs with T_eff > 3000 K, such planets at the inner habitable zone (IHZ) have been shown to retain moist greenhouse conditions, with enhanced stratospheric water vapor (fH₂O > 10⁻³) and low Earth-like surface temperatures. However, M dwarfs also possess strong UV activity, which may effectively photolyze stratospheric H₂O. Prior modeling efforts have not included the impact of high stellar UV activity on the H₂O. Here, we employ a 1D photochemical model with varied stellar UV, to assess whether H₂O destruction driven by high stellar UV would affect its detectability in transmission spectroscopy. Temperature and water vapor profiles are taken from published 3D climate model simulations for an IHZ Earth-sized planet around a 3300 K M dwarf with an N₂–H₂O atmosphere; they serve as self-consistent input profiles for the 1D model. We explore additional chemical complexity within the 1D model by introducing other species into the atmosphere. We find that as long as the atmosphere is well-mixed up to 1 mbar, UV activity appears to not impact detectability of H₂O in the transmission spectrum. The strongest H₂O features occur in the James Webb Space Telescope MIRI instrument wavelength range and are comparable to the estimated systematic noise floor of ∼50 ppm.

We study the orbital evolution and gravitational wave (GW) emission of supermassive black hole (SMBH) binaries formed in gas-free mergers of massive early-type galaxies using the hybrid tree-regularized N-body code Ketju. The evolution of the SMBHs and the surrounding galaxies is followed self-consistently from the large-scale merger down to the final few orbits before the black holes coalesce. Post-Newtonian corrections are included up to PN3.5 level for the binary dynamics, and the GW calculations include the corresponding corrections up to PN1.0-level. We analyze the significance of the stellar environment on the evolution of the binary and the emitted GW signal during the final GW emission dominated phase of the binary hardening and inspiral. Our simulations are compared to semi-analytic models that have often been used for making predictions for the stochastic GW background emitted by SMBHs. We find that the commonly used semi-analytic parameter values produce large differences in merger timescales and eccentricity evolution, but result in only $\sim 10 \%$ differences in the GW spectrum emitted by a single binary at frequencies $f\gtrsim {10}^{-1}\,{\mathrm{yr}}^{-1}$, which are accessible by current pulsar timing arrays. These differences are in part caused by the strong effects of the SMBH binaries on the surrounding stellar population, which are not included in the semi-analytic models.

Given observations of the standard candles and cosmic chronometers, we apply Padé parameterization to the comoving distance and the Hubble parameter to find out how stringently the constraint is set to the curvature parameter by the data. A weak informative prior is introduced in the modeling process to keep the inference away from the singularities. Bayesian evidence for a different order of Padé parameterizations is evaluated during the inference to select the most suitable parameterization in light of the data. The data we used prefer a parameterization form of comoving distance as ${D}_{01}(z)=\tfrac{{a}_{0}z}{1+{b}_{1}z}$ as well as a competitive form ${D}_{02}(z)=\tfrac{{a}_{0}z}{1+{b}_{1}z+{b}_{2}{z}^{2}}$. Similar constraints on the spatial curvature parameter are established by those models and given the Hubble constant as a byproduct: ${{\rm{\Omega }}}_{k}={0.25}_{-0.13}^{+0.14}$ (68% confidence level; CL), H₀ = 67.7 ± 2.0 km s⁻¹ Mpc⁻¹ (68% CL) for D₀₁, and Ω_k = − 0.01 ± 0.13 (68% CL), H₀ = 68.8 ± 2.0 km s⁻¹ Mpc⁻¹ (68% CL) for D₀₂. The evidence from different models demonstrates the qualitative analysis of Padé parameterizations for the comoving distance.

We present a power spectrum analysis of the ALMA Spectroscopic Survey Large Program (ASPECS LP) data from 84 to 115 GHz. These data predominantly probe small-scale fluctuations (k = 10–100 h Mpc⁻¹) in the aggregate CO emission in galaxies at 1≲ z ≲ 4. We place an integral constraint on CO luminosity functions (LFs) in this redshift range via a direct measurement of their second moments in the three-dimensional (3D) autopower spectrum, finding a total CO shot-noise power ${P}_{\mathrm{CO},\mathrm{CO}}({k}_{\mathrm{CO}(2-1)})\leqslant 1.9\times {10}^{2}$μK² (Mpc h⁻¹)³. This upper limit (3σ) is consistent with the observed ASPECS CO LFs in Decarli et al. but rules out a large space in the range of ${P}_{\mathrm{CO},\mathrm{CO}}({k}_{\mathrm{CO}(2-1)})$ inferred from these LFs, which we attribute primarily to large uncertainties in the normalization Φ_* and knee L_* of the Schechter-form CO LFs at z > 2. Also, through power spectrum analyses of ASPECS LP data with 415 positions from galaxies with available optical spectroscopic redshifts, we find that contributions to the observed mean CO intensity and shot-noise power of MUSE galaxies are largely accounted for by ASPECS blind detections. Finally, we sum the fluxes from individual blind CO detections to yield a lower limit on the mean CO surface brightness at 99 GHz of $\langle {T}_{\mathrm{CO}}\rangle =0.55\pm 0.02$μK, which we estimate represents 68%–80% of the total CO surface brightness at this frequency.

We present reverberation-mapping (RM) lags and black hole mass measurements using the C ivλ1549 broad emission line from a sample of 348 quasars monitored as a part of the Sloan Digital Sky Survey RM Project. Our data span four years of spectroscopic and photometric monitoring for a total baseline of 1300 days, allowing us to measure lags up to ∼750 days in the observed frame (this corresponds to a rest-frame lag of ∼300 days in a quasar at z = 1.5 and ∼190 days at z = 3). We report significant time delays between the continuum and the C ivλ1549 emission line in 48 quasars, with an estimated false-positive detection rate of 10%. Our analysis of marginal lag measurements indicates that there are on the order of ∼100 additional lags that should be recoverable by adding more years of data from the program. We use our measurements to calculate black hole masses and fit an updated C iv radius–luminosity relationship. Our results significantly increase the sample of quasars with C iv RM results, with the quasars spanning two orders of magnitude in luminosity toward the high-luminosity end of the C iv radius–luminosity relation. In addition, these quasars are located at some of the highest redshifts (z ≈ 1.4–2.8) of quasars with black hole masses measured with RM. This work constitutes the first large sample of C iv RM measurements in more than a dozen quasars, demonstrating the utility of multiobject RM campaigns.

WD J005311 is a newly identified white dwarf (WD) in a mid-infrared nebula. The spectroscopic observation indicates the existence of a neon-enriched carbon/oxygen wind with a terminal velocity of ${v}_{\infty ,\mathrm{obs}}$ ∼ 16,000 $\mathrm{km}\,{{\rm{s}}}^{-1}$ and a mass-loss rate of ${\dot{M}}_{\mathrm{obs}}\sim 3.5\times {10}^{-6}\,{M}_{\odot }\,{\mathrm{yr}}^{-1}$. Here we consistently explain the properties of WD J005311 using a newly constructed wind solution, where the optically thick outflow is launched from the carbon-burning shell on an oxygen–neon core and accelerated by the rotating magnetic field to become supersonic and unbound well below the photosphere. Our model implies that WD J005311 has a mass of M_* ∼ 1.1–1.3 M_⊙, a magnetic field of B_* ∼ (2–5) × 10⁷ G, and a spin angular frequency of Ω ∼ 0.2–0.5 s⁻¹. The large magnetic field and fast spin support the carbon–oxygen WD merger origin. WD J005311 will neither explode as a type Ia supernova nor collapse into a neutron star. If the wind continues to blow another few kyr, WD J005311 will spin down significantly and join to the known sequence of slowly rotating magnetic WDs. Otherwise it may appear as a fast-spinning magnetic WD and could be a new high-energy source.

We present ALMA observations of the [C ii] 158 μm fine structure line and dust continuum emission from two quasars, SDSS J104433.04−012502.2 and SDSS J012958.51−003539.7, at z = 5.78. The ALMA observations at 02 resolution map the dust and gas on kiloparsec scales. The spatially resolved emission shows a similar trend of decreasing [C ii]–far-infrared (FIR) ratios with increasing FIR surface brightnesses as was found in the infrared luminous galaxies with intense star formation. We confirm the velocity gradients of [C ii] emission found previously in SDSS J0129−0035. No clear evidence of order motion is detected in SDSS J1044−0125. The velocity maps and position–velocity diagrams also suggest turbulent gas clumps in both objects. We tentatively detect a [C ii] peak offset 4.9 kpc to the east of SDSS J1044−0125. This may be associated with an infalling companion, or node of gas outflow. All these results suggest significant dynamical evolution of the interstellar medium in the nuclear region of these young quasar-starburst systems. We fit the velocity map of the [C ii] emission from SDSS J0129−0035 with a rotating disk model. The result suggests a face-on system with an inclination angle of 16° ± 20° and constrains the lower limit of the host galaxy dynamical mass to be 2.6 × 10¹⁰M_⊙ within the [C ii] emitting region. It is likely that SDSS J0129−0035, as well as other young quasars with supermassive black hole masses on the order of 10⁷M_⊙ to 10⁸M_⊙, falls close to the black hole and host galaxy mass relation defined by local galaxies.

Winds from asymptotic giant branch (AGB) stars not only provide mass and energy return, but also produce dust grains in massive elliptical galaxies. Due to the fast stellar velocity, the wind is thought to form a comet-like tail, similar to Mira in the Local Bubble. Many massive elliptical galaxies and cluster centrals host extended dusty cold filaments. We carry out both analytical and numerical studies of the interaction between an AGB wind and the surrounding hot gas. We find that the cooling time of the tail is inversely proportional to the ambient pressure. In the absence of cooling, or in low-pressure environments (e.g., the outskirts of elliptical galaxies), AGB winds are quickly mixed into the hot gas, and all the AGB winds have a similar appearance and head-to-tail ratio. In high-pressure environments, such as the Local Bubble and the central regions of massive elliptical galaxies, some of the gas in the mixing layer between the stellar wind and the surrounding hot gas can cool efficiently and cause the tail to become longer. Our simulated tail of Mira itself has a similar length and velocity to that observed, and appears similar to the simulated AGB tail in the central regions of massive galaxies. While confirmation awaits future studies, we speculate that instead of thermal instability, the induced condensation at the mixing layer of AGB winds may be the origin of cold filaments in massive galaxies and galaxy clusters. This naturally explains the existence of dust and polycyclic aromatic hydrocarbon in the filaments.

Backward-propagating or reverse fluctuations in Alfvénic turbulence are shown to produce magnetic-field-aligned (MFA) electric fields capable of highly intermittent acceleration of particles along the local mean magnetic field. Probability distribution functions (PDFs) for the angles $\chi -{\chi }_{e}$ between magnetic and electric local mean fields in the plane perpendicular to the background magnetic field are calculated both analytically and through Monte Carlo simulations as functions of the fraction $\varepsilon$ of reverse fluctuations. The PDFs peak at $| \chi -{\chi }_{e}| =\pi /2$ but quickly broaden as $\varepsilon$ increases, up to the limit of a uniform PDF for $\varepsilon =0.5$ or zero cross-helicity. Energy from a mixture of forward- and backward-propagating Alfvén waves can easily be transferred to the plasma, through the intermittent MFA electric fields, on a timescale much shorter than the Kolmogorov timescale for turbulence cascade. In such a mixture, for typical 1 au solar wind turbulence parameters, nonresonant interaction through the MFA electric fields rather than gyroresonance controls the energy exchanges between turbulent fields and particles. Possible consequences of the nonresonant interaction through the MFA fields are further suggested, from the observed fast variations of solar wind speed and resulting ${\boldsymbol{v}}$ spectral flattening above 10⁻² Hz, and the turbulence level variability/intermittency near 1 au, to the powering of chromospheric jets/spicules in the upper chromosphere and heating of the chromosphere, transition region, and corona, due to the high reflection rate of Alfvén waves in the upper chromosphere. Conditions for the direct proton acceleration (jet formation) in the chromosphere include a temperature ≤10⁴ K and a magnetic field between about 10 and 100 G.

Most one-dimensional core-collapse simulations fail to explode, yet multidimensional simulations often explode. A dominant multidimensional effect aiding explosion is neutrino-driven convection. We incorporate a convection model in approximate one-dimensional core-collapse supernova (CCSN) simulations. This is the 1D+ method. This convection model lowers the neutrino luminosity required for explosion by $\sim 30$%, similar to the reduction observed in multidimensional simulations. The model is based upon the global turbulence model of Mabanta & Murphy and models the mean-field turbulent flow of neutrino-driven convection. In this preliminary investigation, we use simple neutrino heating and cooling algorithms to compare the critical condition in the 1D+ simulations with the critical condition observed in two-dimensional simulations. Qualitatively, the critical conditions in the 1D+ and the two-dimensional simulations are similar. The assumptions in the convection model affect the radial profiles of density, entropy, and temperature, and comparisons with the profiles of three-dimensional simulations will help to calibrate these assumptions. These 1D+ simulations are consistent with the profiles and explosion conditions of equivalent two-dimensional CCSN simulations but are ∼10² times faster, and the 1D+ prescription has the potential to be ∼10⁵ faster than three-dimensional CCSN simulations. With further calibration, the 1D+ technique could be ideally suited to test the explodability of thousands of progenitor models.

We apply the standard radio pulsar rotating vector model to the white dwarf (WD) pulsar AR Sco's optical polarization position angle swings folded at the WD's spin period as obtained by Buckley et al. Owing to the long duty cycle of spin pulsations with a good signal-to-noise ratio over the entire spin phase, in contrast to neutron star radio pulsars, we find well-constrained values for the magnetic obliquity α and observer viewing direction ζ with respect to the spin axis. We find $\cos \alpha ={0.060}_{-0.053}^{+0.050}$ and $\cos \zeta ={0.49}_{-0.08}^{+0.09}$, implying an orthogonal rotator with an observer angle $\zeta ={60\buildrel{\circ}\over{.} 4}_{-6\buildrel{\circ}\over{.} \,0}^{+5\buildrel{\circ}\over{.} \,3}$. This orthogonal nature of the rotator is consistent with the optical light curve consisting of two pulses per spin period, separated by 180° in phase. Under the assumption that ζ ≈ i, where i is the orbital inclination, and that the companion M star is Roche-lobe-filling, we obtain ${m}_{\mathrm{WD}}={1.00}_{-0.10}^{+0.16}{M}_{\odot }$ for the WD mass. These polarization modeling results suggest the that nonthermal emission arises from a dipolar WD magnetosphere and close to the star, with synchrotron radiation (if nonzero pitch angles can be maintained) being the plausible loss mechanism, marking AR Sco as an exceptional system for future theoretical and observational study.

Observations of sungrazing comets can be used to probe the solar corona, to study the composition of the comets, and to investigate the plasma processes that govern the interaction between the coronal plasma and cometary gas. UVCS observations of the intensities and line profiles of H i Lyα trace the density, temperature, and outflow speed of the corona. Analysis of H i Lyα observations of comet C/2002 S2 showed a surprising split in the comet's Lyα tail and an asymmetry of redshifted and blueshifted emission across the tail axis. It was suggested that the velocity structure might result from a population of neutrals produced by charge transfer between pickup ions and cometary neutrals. Here we present numerical simulations of the H i Lyα intensity and velocity centroid for sungrazing comets under the assumptions that the magnetic field and solar wind are radial. The models qualitatively reproduce the observations of Comet C/2002 S2 and potentially explain the split tail morphology that was seen in C/2002 S2 and also C/2001 C2. They also match the observed red- and blueshifts, though the solar wind velocity needed to explain the blueshift implies strong Doppler dimming and requires a higher outgassing rate to match the light curve. However, the models do not match the observations in detail, and we discuss the remaining discrepancies and the uncertainties in the model. We briefly discuss the implications for other UVCS comet observations and sungrazing comet observations with the Metis coronagraph.

The PAH emission in Spitzer-IRS spectral maps of the reflection nebula NGC 2023 have been previously studied using a Gaussian decomposition method for the 7–9 μm region and a database-fitting approach. Both studies provided insight into the spatial-spectral evolution of the PAH population and related them to changing local physical conditions. This study investigates whether the database-fitting technique provides insight into the PAH populations at the origin of the four Gaussian components. To this end, clustered PAH species maps and spectra are generated from the database-fitting results using spectral clustering utilizing the Structural Similarity Index as an affinity measure. The application of spectral clustering solely based on spatial structure is strongly dependent on the anatomy of the considered regions and is unable to align specific morphological features with a PAH population characterized by a single distinct property. However, in the south FOV the projected distance from the star of the peak emission in a cluster map correlates with the PAH cation fraction and the cluster dominated by small PAHs is confined to the S and SSE ridges, consistent with results from Knight et al. Furthermore, the cluster and Gaussian maps exhibit limited morphological similarity and the 7–9 μm cluster spectra do not show consistent overlap with any of the Gaussian components. However, the relative strengths of the Gaussian components strongly correlate with the PAH ionization parameter as determined from the database-fitting approach. This lends further support to the existence of at least two sub-populations contributing to the 7–9 μm PAH emission.

The supernova remnant HESS J1731-347 is a young supernova remnant (SNR) that displays a nonthermal X-ray and TeV shell structure. A molecular cloud at a distance of ∼3.2 kpc is spatially coincident with the western part of the SNR, and it was likely hit by the SNR. The X-ray emission from this part of the shell is much lower than from the rest of the SNR. Moreover, a compact GeV emission region coincident with the cloud has been detected with a soft spectrum. These observations seem to imply a shock-cloud collision scenario at this area, where the stalled shock can no longer accelerate super-TeV electrons or maintain strong magnetic turbulence downstream, while the GeV cosmic rays (CRs) are released through this stalled shock. To test this hypothesis, we have performed a detailed Fermi-LAT reanalysis of the HESS J1731-347 region with over nine years of data. Two distinct GeV components are found, one displaying a soft spectrum is from the compact GeV emission region, the other one displaying a hard spectrum is from the rest of the SNR (excluding the cloud region). A hadronic model involving a shock-cloud collision scenario is built to explain the γ-ray emission from this area. It consists of three CR sources: run-away super-TeV CRs that have escaped from the fast shock, leaked GeV CRs from the stalled shock, and the local CR sea. The X-ray and γ-ray emission of the SNR excluding the shock-cloud interaction region is explained in a one-zone leptonic model. Our shock-cloud collision model explains the GeV–TeV observations from the clouds around HESS J1731-347, i.e., a cloud in contact with the SNR and a distant cloud in spatial coincidence to the TeV source HESS J1729-345. We find however that the leaked GeV CRs from the shock-cloud collision do not necessarily dominate the GeV emission from the clouds, due to a comparable contribution from the local CR sea.

This paper presents a new analysis of the thermal emission from the neutron star (NS) surface to constrain the dense matter equation of state. We employ an empirical parameterization of the equation of state with a Markov Chain Monte Carlo approach to consistently fit the spectra of quiescent low-mass X-ray binaries in globular clusters with well-measured distances. Despite previous analyses predicting low NS radii, we show that it is possible to reconcile the astrophysical data with nuclear physics knowledge with or without including a prior on the slope of the symmetry energy L_sym. With this empirical parameterization of the equation of state, we obtain radii of the order of about 12 km without worsening the fit statistic. More importantly, we obtain the following values for the slope of the symmetry energy, its curvature K_sym, and the isoscalar skewness parameter Q_sat: ${L}_{\mathrm{sym}}={37.2}_{-8.9}^{+9.2}$ MeV, ${K}_{\mathrm{sym}}=-{85}_{-70}^{+82}$ MeV, and ${Q}_{\mathrm{sat}}={318}_{-366}^{+673}$ MeV. These are the first measurements of the empirical parameters K_sym and Q_sat. Their values are only weakly impacted by our assumptions, such as the distances or the number of free empirical parameters, provided the latter are taken within a reasonable range. We also study the weak sensitivity of our results to the set of sources analyzed, and we identify a group of sources that dominates the constraints. The resulting masses and radii obtained from this empirical parameterization are also compared to other measurements from electromagnetic observations of NSs and gravitational wave signals from the NS–NS merger GW170817.

The processes regulating star formation in galaxies are thought to act across a hierarchy of spatial scales. To connect extragalactic star formation relations from global and kiloparsec-scale measurements to recent cloud-scale resolution studies, we have developed a simple, robust method that quantifies the scale dependence of the relative spatial distributions of molecular gas and recent star formation. In this paper, we apply this method to eight galaxies with ∼1'' resolution molecular gas imaging from the Physics at High Angular resolution in Nearby GalaxieS–ALMA (PHANGS–ALMA) survey and PdBI Arcsecond Whirlpool Survey (PAWS) that have matched resolution, high-quality narrowband Hα imaging. At a common scale of 140 pc, our massive (log(M_⋆[M_⊙]) = 9.3–10.7), normally star-forming (SFR[M_⊙ yr⁻¹] = 0.3–5.9) galaxies exhibit a significant reservoir of quiescent molecular gas not associated with star formation as traced by Hα emission. Galactic structures act as backbones for both molecular gas and H ii region distributions. As we degrade the spatial resolution, the quiescent molecular gas disappears, with the most rapid changes occurring for resolutions up to ∼0.5 kpc. As the resolution becomes poorer, the morphological features become indistinct for spatial scales larger than ∼1 kpc. The method is a promising tool to search for relationships between the quiescent or star-forming molecular reservoir and galaxy properties, but requires a larger sample size to identify robust correlations between the star-forming molecular gas fraction and global galaxy parameters.

Here we present new red sequence overdensity measurements for 77 fields in the high-z Clusters Occupied by Bent Radio AGN (COBRA) survey, based on r- and i-band imaging taken with the Lowell Observatory's Discovery Channel Telescope. We observe 38 COBRA fields in the r-band and 90 COBRA fields in the i-band. By combining the r- and i-band photometry with our 3.6 and 4.5 μm Spitzer IRAC observations, we identify 39 red sequence cluster candidates that host a strong overdensity of galaxies when measuring the excess of red sequence galaxies relative to a background field. We initially treat the radio host as the cluster center and then determine a new cluster center based on the surface density of red sequence sources. Using our color selection, we identify which COBRA cluster candidates have strong red sequence populations. By removing foreground and background contaminants, we more securely determine which fields include cluster candidates with a higher significance than our single-band observations. Additionally, of the 77 fields we analyze with a redshift estimate, 26 include newly estimated photometric redshifts.

The paper investigates the capability of geomagnetic storm parameters in the disturbance storm-time (Dst), Kp, and AE indices to distinguish between severe space weather (SvSW) that causes the reported electric power outages and/or telecommunication failures and normal space weather (NSW) that does not cause these severe effects in a 50 yr period (1958–2007). The parameters include the storm intensities DstMin (minimum Dst during the main phase, MP, of the storm), (dDst/dt)_MPmax, Kp_max, and AE_max. In addition, the impulsive parameter $\mathrm{IpsDst}=(-1/{T}_{\mathrm{MP}}){\int }_{\mathrm{TMP}}| {\mathrm{Dst}}_{\mathrm{MP}}| {dt}$ is derived for the storms that are automatically identified in the Kyoto Dst and USGS $\mathrm{Dst}.{\int }_{\mathrm{TMP}}| {\mathrm{Dst}}_{\mathrm{MP}}| {dt}$ is the integral of the modulus of the Dst from onset of the MP (MPO) to the DstMin. T_MP is the MP duration from MPO to DstMin. The corresponding mean values $\langle {\mathrm{Kp}}_{\mathrm{MP}}\rangle$ and $\langle {\mathrm{AE}}_{\mathrm{MP}}\rangle$ are also calculated. Regardless of the significant differences in the storm parameters between the two Dst indices, the IpsDst in both indices seems to identify four of the five SvSW events (and the Carrington event) in more than 750 NSW events that have been reported to have occurred in 1958–2007, while all other parameters separate one or two SvSWs from the NSWs. Using the Kyoto IpsDst threshold of −250 nT, we demonstrate a 100% true SvSW identification rate with only one false NSW. Using the false NSW event (1972 August 4), we investigate whether using a higher resolution Dst might result in a more accurate identification of SvSWs. The mechanism of the impulsive action leading to large IpsDst and SvSW involves the coincidence that the fast interplanetary coronal mass ejection velocity V contains its shock (or front) velocity $\bigtriangleup V$ and large interplanetary magnetic field Bz southward covering $\bigtriangleup V$.

We present a formalism to extract the H i power spectrum from the epoch of reionization for drift scans using radio interferometers. Our main aim is to determine the coherence timescale of time-ordered visibilities. We compute the two-point correlation function of the H i visibilities measured at different times to address this question. We determine, for a given baseline, the decorrelation of the amplitude and the phase of this complex function. Our analysis uses primary beams of four ongoing and future interferometers—Precision Array for Probing the Epoch of Reionization, Murchison Widefield Array, Hydrogen Epoch of Reionization Array, and Square Kilometre Array (SKA1-Low). We identify physical processes responsible for the decorrelation of the H i signal and isolate their impact by making suitable analytic approximations. The decorrelation timescale of the amplitude of the correlation function lies in the range of 2–20 minutes for baselines of interest for the extraction of the H i signal. The phase of the correlation function can be made small after scaling out an appropriate term, which also causes the coherence timescale of the phase to be longer than the amplitude of the correlation function. We find that our results are insensitive to the input H i power spectrum, and therefore, they are directly applicable to the analysis of the drift scan data. We also apply our formalism to a set of point sources and statistically homogeneous diffuse correlated foregrounds. We find that point sources decorrelate on a timescale much shorter than the H i signal. This provides a novel mechanism to partially mitigate the foregrounds in a drift scan.

Detections of gravitational waves are now starting to probe the mass distribution of stellar mass black holes (BHs). Robust predictions from stellar models are needed to interpret these. Theory predicts the existence of a gap in the BH mass distribution because of pair-instability supernovae. The maximum BH mass below the gap is the result of pulsational mass loss. We evolve massive helium stars through their late hydrodynamical phases of evolution using the open-source MESA stellar evolution code. We find that the location of the lower edge of the mass gap at 45 ${M}_{\odot }$ is remarkably robust against variations in the metallicity (≈3 ${M}_{\odot }$), the treatment of internal mixing (≈1 ${M}_{\odot }$), and stellar wind mass loss (≈4 ${M}_{\odot }$), making it the most robust predictor for the final stages of the evolution of massive stars. The reason is that the onset of the instability is dictated by the near-final core mass, which in turn sets the resulting BH mass. However, varying the ${}^{12}{\rm{C}}{\left(\alpha ,\gamma \right)}^{16}{\rm{O}}$ reaction rate within its 1σ uncertainties shifts the location of the gap between 40 ${M}_{\odot }$ and 56 ${M}_{\odot }$. We provide updated analytic fits for population synthesis simulations. Our results imply that the detection of merging BHs can provide constraints on nuclear astrophysics. Furthermore, the robustness against metallicity suggests that there is a universal maximum for the location of the lower edge of the gap, which is insensitive to the formation environment and redshift for first-generation BHs. This is promising for the possibility to use the location of the gap as a "standard siren" across the universe.

Atomic oxygen (O⁰) plays a critical role in determining the structure of photon-dominated regions (PDRs), but reliable modeling of its emission has been hampered by the high optical depth of the 63 μm fine structure line and complexities in the excitation of the relevant fine structure levels. We discuss here radiation produced by collisional excitation of the submillimeter fine structure lines of atomic oxygen ([O I]) using recent calculations of rates for collisions with atomic and molecular hydrogen. We employ the Molpop–CEP code to include the effects of optical thickness in slab models that are characterized by uniform oxygen abundance, hydrogen density, and kinetic temperature. The particular spontaneous decay rates and collisional excitation rates connecting the three O⁰ fine structure levels result in population inversion of the upper, 145 μm transition. The effects of trapping are rigorously included and are reflected in the resulting line profiles that exhibit prominent self-absorption even with uniform physical conditions. We present figures for analyzing the two fine structure lines based on the intensity of the 63 μm line and the 145 μm/63 μm line ratio. For the clouds considered, the results for line intensities and line ratios are modestly different from those obtained with a large-velocity-gradient model, but the ability to calculate line profiles is an additional powerful tool. Comparison of the model results with observed line profiles suggests that cloud models with varying physical conditions are required to optimally utilize [O I] fine structure line emission to trace the energetics of PDR regions and the feedback from massive, young stars.

We present a physical characterization of MM J100026.36+021527.9 (a.k.a. "Mambo-9"), a dusty star-forming galaxy (DSFG) at z = 5.850 ± 0.001. This is the highest-redshift unlensed DSFG (and fourth most distant overall) found to date and is the first source identified in a new 2 mm blank-field map in the COSMOS field. Though identified in prior samples of DSFGs at 850 μm to 1.2 mm with unknown redshift, the detection at 2 mm prompted further follow-up as it indicated a much higher probability that the source was likely to sit at z > 4. Deep observations from the Atacama Large Millimeter and submillimeter Array (ALMA) presented here confirm the redshift through the secure detection of ¹²CO(J = 6→5) and p-H₂O (2_1,1 → 2_0,2). Mambo-9 is composed of a pair of galaxies separated by 6 kpc with corresponding star formation rates of 590 M_⊙ yr⁻¹ and 220 M_⊙ yr⁻¹, total molecular hydrogen gas mass of (1.7 ± 0.4) × 10¹¹M_⊙, dust mass of (1.3 ± 0.3) × 10⁹M_⊙, and stellar mass of (${3.2}_{-1.5}^{+1.0}$) × 10⁹M_⊙. The total halo mass, (3.3 ± 0.8) × 10¹²M_⊙, is predicted to exceed 10¹⁵M_⊙ by z = 0. The system is undergoing a merger-driven starburst that will increase the stellar mass of the system tenfold in τ_depl = 40−80 Myr, converting its large molecular gas reservoir (gas fraction of ${96}_{-2}^{+1} \%$) into stars. Mambo-9 evaded firm spectroscopic identification for a decade, following a pattern that has emerged for some of the highest-redshift DSFGs found. And yet, the systematic identification of unlensed DSFGs like Mambo-9 is key to measuring the global contribution of obscured star formation to the star formation rate density at z ≳ 4, the formation of the first massive galaxies, and the formation of interstellar dust at early times (≲1 Gyr).

The second Hi-C flight (Hi-C 2.1) provided unprecedentedly high spatial and temporal resolution (∼250 km, 4.4 s) coronal EUV images of Fe ix/x emission at 172 Å of AR 12712 on 2018 May 29, during 18:56:21–19:01:56 UT. Three morphologically different types (I: dot-like; II: loop-like; III: surge/jet-like) of fine-scale sudden-brightening events (tiny microflares) are seen within and at the ends of an arch filament system in the core of the AR. Although type Is (not reported before) resemble IRIS bombs (in size, and brightness with respect to surroundings), our dot-like events are apparently much hotter and shorter in span (70 s). We complement the 5 minute duration Hi-C 2.1 data with SDO/HMI magnetograms, SDO/AIA EUV images, and IRIS UV spectra and slit-jaw images to examine, at the sites of these events, brightenings and flows in the transition region and corona and evolution of magnetic flux in the photosphere. Most, if not all, of the events are seated at sites of opposite-polarity magnetic flux convergence (sometimes driven by adjacent flux emergence), implying likely flux cancellation at the microflare's polarity inversion line. In the IRIS spectra and images, we find confirming evidence of field-aligned outflow from brightenings at the ends of loops of the arch filament system. In types I and II the explosion is confined, while in type III the explosion is ejective and drives jet-like outflow. The light curves from Hi-C, AIA, and IRIS peak nearly simultaneously for many of these events, and none of the events display a systematic cooling sequence as seen in typical coronal flares, suggesting that these tiny brightening events have chromospheric/transition region origin.

The original concept of self-organized criticality, applied to solar flare statistics, assumed a slow-driven and stationary flaring rate, which implies timescale separation (between flare durations and interflare waiting times). The concept reproduces power-law distributions for flare peak fluxes and durations, but predicts an exponential waiting time distribution. In contrast to these classical assumptions, we observe (i) multiple energy dissipation episodes during most flares, (ii) violation of the principle of timescale separation, (iii) a fast-driven and nonstationary flaring rate, (iv) a power-law distribution for waiting times Δt, with a slope of α_Δt ≈ 2.0, as predicted from the universal reciprocality between mean flaring rates and mean waiting times, and (v) pulses with rise times and decay times of the dissipated magnetic free energy on timescales of 12 ± 6 minutes, and up to 13 times in long-duration (≲4 hr) flares. These results are inconsistent with coronal long-term energy storage, but require photospheric–chromospheric current injections into the corona.

We revisit the rates of neutrino pair emission and absorption from nucleon–nucleon bremsstrahlung in supernova matter using the T-matrix formalism in the long-wavelength limit. Based on two-body potentials of chiral effective field theory (χEFT), we solve the Lippmann–Schwinger equation for the T-matrix including non-diagonal contributions. We consider final-state Pauli blocking and hence our calculations are valid for nucleons with an arbitrary degree of degeneracy. We also explore the in-medium effects on the T-matrix and find that they are relatively small for supernova matter. We compare our results with one-pion exchange rates, commonly used in supernova simulations, and calculations using an effective on-shell diagonal T-matrix from measured phase shifts. We estimate that multiple-scattering effects and correlations due to the random phase approximation introduce small corrections on top of the T-matrix results at subsaturation densities. A numerical table of the structure function is provided that can be used in supernova simulations.

We present a statistical analysis of the flybys of dark matter halos compared to mergers, using cosmological N-body simulations. We mainly focus on gravitationally interacting target halos with mass of 10^10.8–10^13.0h⁻¹M_⊙, and their neighbors are counted only when the mass ratio is 1:3–3:1 and the distance is less than the sum of the virial radii of target and neighbor. The neighbors are divided into the flyby or merger samples if the pair's total energy is greater or smaller, respectively, than the capture criterion with consideration of dynamical friction. The main results are as follows: (a) the flyby fraction increases by up to a factor of 50 with decreasing halo mass and by up to a factor of 400 with increasing large-scale density, while the merger fraction does not show any significant dependencies on these two parameters; (b) the redshift evolution of the flyby fraction is twofold, increasing with redshift at 0 < z < 1 and remaining constant at z > 1, while the merger fraction increases monotonically with redshift at z = 0 ∼ 4; (c) Multiple interactions with two or more neighbors are on average flyby-dominated, and their fraction has a mass and environment dependence similar to that for the flyby fraction; and (d) Given that flybys substantially outnumber mergers toward z = 0 (by a factor of five) and the multiple interactions are flyby-dominated, the flyby's contribution to galactic evolution is stronger than ever at the present epoch, especially for less massive halos and in the higher density environment. We propose a scenario that connects the evolution of the flyby and merger fractions to the hierarchical structure formation process.

Spectral lines of heavy atomic elements in the ejecta of supernovae and neutron star mergers can have important contribution to the opacity of the ejecta matter even when the abundance of the elements is very small. Under favorable conditions, the line expansion opacity arising from spectral lines and the expansion of the medium can be orders of magnitude larger than the opacity of electron scattering. In this paper, we derive the formulae for evaluating the line expansion opacity and its Rosseland mean in an expanding medium in the framework of special relativity, which can be considered as a generalization of previous work in the Newtonian approximation. Then we compare the derived relativistic formulae to the Newtonian ones to explore the relativistic effect on the opacity and test the new formulae with the spectral lines of some heavy atomic elements. We also derive some approximation formulae for the Rosseland mean of the line expansion opacity that are easy to use in numerical works while still maintaining a high-enough accuracy relative to exact solutions. The formulae derived in this paper are expected to have important applications in radiative problems related to relativistic astrophysical phenomena such as neutron star mergers, supernovae, and gamma-ray bursts where relativistic or subrelativistic expansions are involved.

Recent Lyα forest tomography measurements of the intergalactic medium (IGM) have revealed a wealth of cosmic structures at high redshift (z ∼ 2.5). In this work, we present the Tomographic Absorption Reconstruction and Density Inference Scheme (TARDIS), a new chronocosmographic analysis tool for understanding the formation and evolution of these observed structures. We use maximum likelihood techniques with a fast nonlinear gravitational model to reconstruct the initial density field of the observed regions. We find that TARDIS allows accurate reconstruction of smaller-scale structures than standard Wiener-filtering techniques. Applying this technique to mock Lyα forest data sets that simulate ongoing and future surveys such as CLAMATO, Subaru PFS, or the ELTs, we are able to infer the underlying matter density field at observed redshift and classify the cosmic web structures. We find good agreement with the underlying truth in both the characteristic eigenvalues and eigenvectors of the pseudo-deformation tensor, with the eigenvalues inferred from 30 m class telescopes correlated at r = 0.95 relative to the truth. As an output of this method, we are able to further evolve the inferred structures to late time (z = 0) and also track the trajectories of coeval z = 2.5 galaxies to their z = 0 cosmic web environments.

We describe a star cluster formation model that includes individual star formation from self-gravitating, magnetized gas, coupled to collisional stellar dynamics. The model uses the Astrophysical Multi-purpose Software Environment to integrate an adaptive-mesh magnetohydrodynamics code (FLASH) with a fourth order Hermite N-body code (ph4), a stellar evolution code (SeBa), and a method for resolving binary evolution (multiples). This combination yields unique star-formation simulations that allow us to study binaries formed dynamically from interactions with both other stars and dense, magnetized gas subject to stellar feedback during the birth and early evolution of stellar clusters. We find that for massive stars, our simulations are consistent with the observed dynamical binary fractions and mass ratios. However, our binary fraction drops well below observed values for lower mass stars, presumably due to unincluded binary formation during initial star formation. Further, we observe a buildup of binaries near the hard-soft boundary that may be an important mechanism driving early cluster contraction.

Solar wind ions are observed to be heated in the directions perpendicular to the large-scale magnetic field, with preferential heating given to heavy ions. In the solar corona, this heating may be responsible for the generation of the wind itself. It is likely that this heating results from the dissipation of plasma turbulence, but the specific kinetic mechanism that produces these preferential effects is not known. Solar wind turbulence at proton scales is often characterized in terms of highly oblique kinetic Alfvén waves (KAWs), which have been thought to dissipate through the Landau resonance and yield parallel heating. We show that the quasilinear resonant cyclotron interaction between KAWs and solar wind ions can actually produce perpendicular ion heating. We present an illustrative calculation of a steady, critically balanced spectrum of KAWs acting on homogeneous ion distributions with a plasma β = 0.1, representative of turbulent conditions in the fast solar wind near 20 R_s. The KAWs are described here by a two-fluid dispersion relation. We find that thermal protons are strongly heated in the perpendicular direction within a typical quasilinear time of several thousand gyroperiods, which corresponds to only a few minutes at 20 R_s. Alpha particles in the same fluctuation field are heated to similar perpendicular thermal speeds, equivalent to the greater than mass proportional perpendicular temperatures that are commonly observed. We discuss improvements to this simple model that may determine whether this mechanism can be responsible for the observed coronal and solar wind ion heating.

We compare the coronal magnetic energy and helicity of two solar active regions (ARs), prolific in major eruptive (AR 11158) and confined (AR 12192) flaring, and analyze the potential of deduced proxies to forecast upcoming flares. Based on nonlinear force-free (NLFF) coronal magnetic field models with a high degree of solenoidality, and applying three different computational methods to investigate the coronal magnetic helicity, we are able to draw conclusions with a high level of confidence. Based on real observations of two solar ARs we checked trends regarding the potential eruptivity of the active-region corona, as suggested earlier in works that were based on numerical simulations, or solar observations. Our results support that the ratio of current-carrying to total helicity, $| {H}_{{\rm{J}}}| /| {H}_{{ \mathcal V }}|$, shows a strong ability to indicate the eruptive potential of a solar AR. However, $| {H}_{{\rm{J}}}| /| {H}_{{ \mathcal V }}|$ does not seem to be indicative for the magnitude or type of an upcoming flare (confined or eruptive). Interpreted in the context of earlier observational studies, our findings furthermore support that the total relative helicity normalized to the magnetic flux at the NLFF model's lower boundary, ${H}_{{ \mathcal V }}/{\phi }^{2}$, represents no indicator for the eruptivity.

We describe a revised procedure for the numerical simulation of planetary nebulae luminosity functions (PNLFs), improving on previous work. The procedure is now based on new H-burning post-asymptotic giant branch (AGB) evolutionary tracks. For a given stellar mass, the new central stars are more luminous and evolve faster. We have slightly changed the distribution of the [O iii] 5007 intensities relative to those of ${\rm{H}}\beta$ and the generation of absorbing factors, while still basing their numerical modeling on empirical information extracted from studies of galactic planetary nebulae (PNs) and their central stars. We argue that the assumption of PNs being completely optically thick to H-ionizing photons leads to conflicts with observations and show that to account for optically thin PNs is necessary. We then use the new simulations to estimate a maximum final mass, clarifying its meaning, and discuss the effect of internal dust extinction as a possible way of explaining the persistent discrepancy between PNLFs and surface brightness fluctuation distances. By adjusting the range of minimum to maximum final mass, it is also possible to explain the observed variety of PNLF shapes at intermediate magnitudes. The new PN formation rates are calculated to be slightly lower than suggested by previous simulations based on older post-AGB evolutionary tracks.

Many more supernova remnants (SNRs) are now known in external galaxies than in the Milky Way. Most of these SNRs have been identified using narrowband imaging, separating SNRs from H ii regions on the basis of [S ii]:Hα ratios that are elevated compared to H ii regions. However, the boundary between SNRs and H ii regions is not always distinct, especially at low surface brightness. Here we explore velocity structure as a possible criterion for separating SNRs from H ii regions, using a sample of well-studied SNRs in the Large Magellanic Cloud as well as a small number of SNRs in the galaxy M83. We find, perhaps not surprisingly, that even at large diameters, SNRs exhibit velocity broadening sufficient to readily distinguish them from H ii regions. We thus suggest that the purity of most extragalactic samples would be greatly improved through spectroscopic observations with a velocity resolution of order 50 km s⁻¹.

The origin of bistable solutions in the kinetic equations describing the chemistry of dense interstellar clouds is explained as being due to the autocatalysis and feedback of oxygen nuclei from the oxygen dimer (O₂). We identify four autocatalytic processes that can operate in dense molecular clouds, driven respectively by reactions of H⁺, He⁺, C⁺, and S⁺ with O₂. We show that these processes can produce the bistable solutions found in previous studies, as well as the dependence on various model parameters such as the helium ionization rate, the sulfur depletion and the ${{\rm{H}}}_{3}^{+}$ electron recombination rate. We also show that ion–grain neutralizations are unlikely to affect the occurrence of bistability in dense clouds. It is pointed out that many chemical models of astronomical sources should have the potential to show bistable solutions.

Some binary systems composed of a white dwarf (WD) and a hot subdwarf (sdB) helium star will make contact within the helium burning lifetime of the sdB star. The accreted helium on the WD inevitably undergoes a thermonuclear instability, causing a detonation that is expected to transition into the WD core and lead to a thermonuclear supernova (SN) while the donor orbits nearby with high velocity. Motivated by the recent discovery of fast moving objects that occupy unusual locations on the HR diagram, we explore the impact of the thermonuclear SNe on the donors in this specific double detonation scenario. We use MESA to model the binary up to the moment of detonation, then 3D Athena++ to model the hydrodynamic interaction of the SN ejecta with the donor star, calculating the amount of mass that is stripped and the entropy deposited in the deep stellar interior by the strong shock that traverses it. We show that these donor remnants are ejected with velocities primarily set by their orbital speeds: 700–900 km s⁻¹. We model the long-term thermal evolution of remnants by introducing the shock entropy into MESA models. In response to this entropy change, donor remnants expand and brighten for timescales ranging from 10⁶ to 10⁸ yr, giving ample time for these runaway stars to be observed in their inflated state before they leave the galaxy. Even after surface layers are stripped, some donors retain enough mass to resume core helium burning and further delay fading for more than 10⁸ yr.

We present new XMM-Newton and NuSTAR observations of the galaxy merger IRAS F05189-2524, which is classified as an ultraluminous infrared galaxy and optical Seyfert 2 at z = 0.0426. We test a variety of spectral models that yield a best fit consisting of an absorbed power law with emission and absorption features in the Fe K band. Remarkably, we find evidence for a blueshifted Fe K absorption feature at E = 7.8 keV (rest frame) which implies an ultrafast outflow (UFO) with v_out = 0.11 ± 0.01c. We calculate that the UFO in IRAS F05189-2524 has a mass outflow rate of ${\dot{M}}_{\mathrm{out}}\ \gtrsim 1.0\ {M}_{\odot }$ yr⁻¹, a kinetic power of ${\dot{E}}_{{\rm{K}}}\,\gtrsim$ 8% L_AGN, and a momentum rate (or force) of ${\dot{P}}_{\mathrm{out}}\ \gtrsim 1.4\ {L}_{\mathrm{AGN}}/c$. Comparing the energetics of the UFO to the observed multi-phase outflows at kiloparsec scales yields an efficiency factor of f ∼ 0.05 for an energy-driven outflow. Given the uncertainties, however, we cannot exclude the possibility of a momentum-driven outflow. Comparing IRAS F05189-2524 with nine other objects with observed UFOs and large-scale galactic outflows suggests that there is a range of efficiency factors for the coupling of the energetics of the nuclear and galaxy-scale outflows that likely depend on specific physical conditions in each object.

Besides buckminsterfullerene (C₆₀), other fullerenes and their derivatives may also reside in space. In this work, we study the formation and photodissociation processes of astronomically relevant fullerene/anthracene (C₁₄H₁₀) cluster cations in the gas phase. Experiments are carried out using a quadrupole ion trap in combination with time-of-flight mass spectrometry. The results show that fullerene (C₆₀ and C₇₀)/anthracene (i.e., [(C₁₄H₁₀)_nC₆₀]⁺ and [(C₁₄H₁₀)_nC₇₀]⁺), fullerene (C₅₆ and C₅₈)/anthracene (i.e., [(C₁₄H₁₀)_nC₅₆]⁺ and [(C₁₄H₁₀)_nC₅₈]⁺), and fullerene (C₆₆ and C₆₈)/anthracene (i.e., [(C₁₄H₁₀)_nC₆₆]⁺ and [(C₁₄H₁₀)_nC₆₈]⁺) cluster cations, are formed in the gas phase through an ion–molecule reaction pathway. With irradiation, all the fullerene/anthracene cluster cations dissociate into monoanthracene and fullerene species without dehydrogenation. The structure of newly formed fullerene/anthracene cluster cations and the bonding energy for these reaction pathways are investigated with quantum chemistry calculations. Our results provide a growth route toward large fullerene derivatives in a bottom-up process and insight into their photoevolution behavior in the interstellar medium, and clearly, when conditions are favorable, fullerene/polycyclic aromatic hydrocarbon clusters can form efficiently. In addition, these clusters (from 80 to 154 atoms or ∼2 nm in size) offer a good model for understanding the physical–chemical processes involved in the formation and evolution of carbon dust grains in space, and provide candidates of interest for the diffuse interstellar bands that could motivate spectroscopic studies.

We report on observations of the two newly identified reconnection geometries involving erupting flux ropes. In 3D, a flux rope can reconnect either with a surrounding coronal arcade (recently named "ar–rf" reconnection) or with itself ("rr–rf" reconnection), and both kinds of reconnection create a new flux-rope field line and a flare loop. For the first time, we identify all four constituents of both reconnections in a solar eruptive event, the filament eruption of 2011 June 7 observed by Solar Dynamics Observatory/Atmospheric Imaging Assembly. The ar–rf reconnection manifests itself as shift of one leg of the filament by more than 25'' northward. At its previous location, a flare arcade is formed, while the new location of the filament leg previously corresponded to a footpoint of a coronal loop in 171 Å. In addition, the evolution of the flare ribbon hooks is also consistent with the occurrence of ar–rf reconnection as predicted by MHD simulations. Specifically, the growing hook sweeps footpoints of preeruptive coronal arcades, and these locations become inside the hook. Furthermore, the rr–rf reconnection occurs during the peak phase above the flare arcade, in an apparently X-type geometry involving a pair of converging bright filament strands in the erupting filament. A new flare loop forms near the leg of one of the strands, while a bright blob, representing a remnant of the same strand, is seen ascending into the erupting filament. All together, these observations vindicate recent predictions of the 3D standard solar-flare model.

We calculate the evolution of massive stars, which undergo pulsational pair-instability (PPI) when the O-rich core is formed. The evolution from the main sequence through the onset of PPI is calculated for stars with initial masses of 80–140 M_⊙ and metallicities of Z = 10⁻³−1.0 Z_⊙. Because of mass loss, Z ≤ 0.5 Z_⊙ is necessary for stars to form He cores massive enough (i.e., mass >40 M_⊙) to undergo PPI. The hydrodynamical phase of evolution from PPI through the beginning of Fe-core collapse is calculated for He cores with masses of 40−62 M_⊙ and Z = 0. During PPI, electron–positron pair production causes a rapid contraction of the O-rich core, which triggers explosive O-burning and a pulsation of the core. We study the mass dependence of the pulsation dynamics, thermodynamics, and nucleosynthesis. The pulsations are stronger for more massive He cores and result in a large amount of mass ejection such as 3–13 M_⊙ for 40−62 M_⊙ He cores. These He cores eventually undergo Fe-core collapse. The 64 M_⊙ He core undergoes complete disruption and becomes a pair-instability supernova. The H-free circumstellar matter ejected around these He cores is massive enough to explain the observed light curve of Type I (H-free) superluminous supernovae with circumstellar interaction. We also note that the mass ejection sets the maximum mass of black holes (BHs) to be ∼50 M_⊙, which is consistent with the masses of BHs recently detected by VIRGO and aLIGO.

Chemical tagging seeks to identify unique star formation sites from present-day stellar abundances. Previous techniques have treated each abundance dimension as being statistically independent, despite theoretical expectations that many elements can be produced by more than one nucleosynthetic process. In this work, we introduce a data-driven model of nucleosynthesis, where a set of latent factors (e.g., nucleosynthetic yields) contribute to all stars with different scores and clustering (e.g., chemical tagging) is modeled by a mixture of multivariate Gaussians in a lower-dimensional latent space. We use an exact method to simultaneously estimate the factor scores for each star, the partial assignment of each star to each cluster, and the latent factors common to all stars, even in the presence of missing data entries. We use an information-theoretic Bayesian principle to estimate the number of latent factors and clusters. Using the second Galah data release, we find that six latent factors are preferred to explain N = 2566 stars with 17 chemical abundances. We identify the rapid- and slow neutron-capture processes, as well as latent factors consistent with Fe-peak and α-element production, and another where K and Zn dominate. When we consider N ∼ 160,000 stars with missing abundances, we find another seven factors, as well as 16 components in latent space. Despite these components showing separation in chemistry, which is explained through different yield contributions, none show significant structure in their positions or motions. We argue that more data and joint priors on cluster membership that are constrained by dynamical models are necessary to realize chemical tagging at a galactic-scale. We release accompanying software that scales well with the available data, allowing for the model's parameters to be optimized in seconds given a fixed number of latent factors, components, and ∼10⁷ abundance measurements.

We present ALMA observations and multiwavelength spectral energy distribution analysis in a Wide-field Infrared Survey Explorer-selected, hyperluminous dust-obscured quasar W0533−3401 at z = 2.9. We derive the physical properties of each of its components, such as molecular gas, stars, dust, and the central supermassive black hole (SMBH). Both the dust continuum at 3 mm and the CO $(3\mbox{--}2)$ line are detected. The derived molecular gas mass M_gas = 8.4 × 10¹⁰M_⊙ and its fraction f_gas = 0.7 suggest that W0533−3401 is gas-rich. The star formation rate (SFR) has been estimated to be ∼3000–7000 M_⊙ yr⁻¹ by using different methods. The high values of SFR and specific SFR suggest that W0533−3401 is a maximum starburst. The corresponding gas depletion timescales are very short (t_depl ∼ 12–28 Myr). The CO $(3\mbox{--}2)$ emission line is marginally resolved and has a velocity gradient, which is possibly due to a rotating gas disk, gas outflow, or merger. Finally, we infer the black hole mass growth rate of W0533−3401 (${\dot{M}}_{\mathrm{BH}}=49$M_⊙ yr⁻¹), which suggests a rapid growth of the central SMBH. The observed black hole to stellar mass ratio M_BH/M_⋆  of W0533−3401, which is dependent on the adopted Eddington ratio, is over one order of magnitude higher than the local value, and is evolving toward the evolutionary trend of unobscured quasars. Our results are consistent with the scenario that W0533−3401, with both a gas-rich maximum starburst and a rapid black hole growth, is experiencing a short transition phase toward an unobscured quasar.

Supernova (SN) 2014C is unique: a seemingly typical hydrogen-poor SN that started to interact with a dense, hydrogen-rich circumstellar medium (CSM) ∼100 days post-explosion. The delayed interaction suggests a detached CSM shell, unlike in a typical SN IIn where the CSM is much closer and the interaction commences earlier post-explosion, indicating a different mass-loss history. We present infrared observations of SN 2014C 1–5 yr post-explosion, including uncommon 9.7 μm imaging with COMICS on the Subaru telescope. Spectroscopy shows the intermediate-width He I 1.083 μm emission from the interacting region up to the latest epoch 1639 days post-explosion. The last Spitzer/IRAC photometry at 1920 days confirms ongoing CSM interaction. The 1–10 μm spectral energy distributions (SEDs) can be explained by a dust model with a mixture of 62% carbonaceous and 38% silicate dust, pointing to a chemically inhomogeneous CSM. The inference of silicate dust is the first among interacting SNe. An SED model with purely carbonaceous CSM dust, while possible, requires more than 0.22 M_⊙ of dust, an order of magnitude larger than what has been observed in any SNe at this epoch. The light curve beyond 500 days is well fit by an interaction model with a wind-driven CSM and a mass-loss rate of ∼10⁻³M_⊙ yr⁻¹, which presents an additional CSM density component exterior to the constant-density shell reported previously in the literature. SN 2014C could originate in a binary system, similar to RY Scuti, which would explain the observed chemical and density profile inhomogeneity in the CSM.

We present a detailed high-resolution weak-lensing study of SPT-CL J2106-5844 at z = 1.132, claimed to be the most massive system discovered at z > 1 in the South Pole Telescope Sunyaev–Zel'dovich survey. Based on the deep imaging data from the Advanced Camera for Surveys and Wide Field Camera 3 on board the Hubble Space Telescope, we find that the cluster mass distribution is asymmetric, composed of a main clump and a subclump ∼640 kpc west thereof. The central clump is further resolved into two smaller northwestern and southeastern substructures separated by ∼150 kpc. We show that this rather complex mass distribution is more consistent with the cluster galaxy distribution than a unimodal distribution as previously presented. The northwestern substructure coincides with the brightest cluster galaxy and the X-ray peak while the southeastern one agrees with the location of the peak in number density. These morphological features and the comparison with the X-ray emission suggest that the cluster might be a merging system. We estimate the virial mass of the cluster to be ${M}_{200c}=({10.4}_{-3.0}^{+3.3}\pm 1.0)\times$${10}^{14}\,{M}_{\odot }$, where the second error bar is the systematic uncertainty. Our result confirms that the cluster SPT-CL J2106-5844 is indeed the most massive cluster at z > 1 known to date. We demonstrate the robustness of this mass estimate by performing a number of tests with different assumptions on the centroids, mass–concentration relations, and sample variance.

New analytical steady-state and time-dependent solutions for the acceleration of energetic particles by contracting and reconnecting small-scale flux ropes (SMFRs) in the solar wind are presented. For this purpose, a telegrapher-type Parker transport equation was derived from the existing underlying focused transport equation. The solutions unify all SMFR acceleration mechanisms present in the transport equation, showing that SMFR acceleration by the reconnection electric field in the mixed-derivative transport term is constrained by and requires the presence of second-order Fermi SMFR acceleration. We explore the potential of these solutions in reproducing energetic proton flux enhancements and spectral evolution between ∼50 keV and 5 MeV in dynamic SMFR regions near large-scale reconnecting current sheets in the solar wind at Earth orbit. It is shown that second-order Fermi SMFR acceleration involving the variance in SMFR compression and incompressible parallel shear flow and confirmed that first-order SMFR Fermi acceleration, due to mean SMFR compression (successfully used before in data fits), are both workable options in reproducing observed flux amplification factors when using reasonable SMFR parameters. However, the predicted substantial quantitative differences in the spatial evolution of the accelerated spectra through the SMFR region might provide a way to distinguish between first- and second-order Fermi SMFR acceleration in observations. It is concluded that more detailed data analysis of SMFR parameters in SMFR acceleration events is needed before the relative role of first- and second-order SMFR acceleration mechanisms can be determined.

Rich complexes of associated absorption lines (AALs) in quasar spectra provide unique information about gaseous infall, outflows, and feedback processes in quasar environments. We study five quasars at redshifts z ~ 3.1–4.4 with AAL complexes containing from 7 to 18 C iv λ1548, 1551 systems in high-resolution spectra. These complexes span velocity ranges ≲3600 km s⁻¹ within ≲8200 km s⁻¹ of the quasar redshifts. All are highly ionized with no measurable low-ionization ions like Si ii or C ii, and all appear to form in the quasar/host galaxy environments based on evidence for line locking, partial covering of the background light source, strong N v absorption, and/or roughly solar metallicities, and on the implausibility of such complexes forming in unrelated intervening galaxies. Most of the lines in all five complexes identify high-speed quasar-driven outflows at velocity shifts $v\lesssim -1000$ km s⁻¹. Four of the complexes also have lines at smaller blueshifted velocities that might form in ambient interstellar clouds, low-speed outflows, or at feedback interfaces in the host galaxies where high-speed winds impact and shred interstellar clouds. The partial covering we measure in some of the high-speed outflow lines require small absorbing clouds with characteristic sizes ≲1 pc or ≲0.01 pc. The short survival times of these clouds require locations very close to the quasars, or cloud creation in situ at larger distances perhaps via feedback/cloud-shredding processes. The AAL complex in one quasar, J1008+3623, includes unusually narrow C iv systems at redshifted velocities $350\lesssim v\lesssim 640$ km s⁻¹ that are excellent candidates for gaseous infall toward the quasar, e.g., "cold-mode" accretion or a gravitationally bound galactic fountain.

G23.33-0.30 is a 600 M_⊙ infrared dark molecular filament that exhibits large NH₃ velocity dispersions (σ ∼ 8 km s⁻¹) and bright, narrow NH₃(3, 3) line emission. We have probed G23.33-0.30 at the < 0.1 pc scale and confirmed that the narrow NH₃(3, 3) line is emitted by four rare NH₃(3, 3) masers, which are excited by a large-scale shock impacting the filament. G23.33-0.30 also displays a velocity gradient along its length, a velocity discontinuity across its width, shock-tracing SiO(5–4) emission extended throughout the filament, and broad turbulent line widths in NH₃(1, 1) through (6, 6), CS(5–4), and SiO(5–4), as well as an increased NH₃ rotational temperature (T_rot) and velocity dispersion (σ) associated with the shocked, blueshifted component. The correlations among T_rot, σ, and V_LSR imply that the shock is accelerating, heating, and adding turbulent energy to the filament gas. Given G23.33-0.30's location within the giant molecular cloud G23.0-0.4, we speculate that the shock and NH₃(3, 3) masers originated from the supernova remnant (SNR) W41, which exhibits additional evidence of an interaction with G23.0-0.4. We have also detected the 1.3 mm dust continuum emission from at least three embedded molecular cores associated with G23.33-0.30. Although the cores have moderate gas masses (M = 7–10 M_⊙), their large virial parameters (α = 4–9) suggest that they will not collapse to form stars. The turbulent line widths of the (α > 1) cores may indicate negative feedback due to the SNR shock.

The distribution of metals within a galaxy traces the baryon cycle and the buildup of galactic disks, but the detailed gas phase metallicity distribution remains poorly sampled. We have determined the gas phase oxygen abundances for 7138 H ii regions across the disks of eight nearby galaxies using Very Large Telescope/Multi Unit Spectroscopic Explorer (MUSE) optical integral field spectroscopy as part of the PHANGS–MUSE survey. After removing the first-order radial gradients present in each galaxy, we look at the statistics of the metallicity offset (ΔO/H) and explore azimuthal variations. Across each galaxy, we find low (σ = 0.03–0.05 dex) scatter at any given radius, indicative of efficient mixing. We compare physical parameters for those H ii regions that are 1σ outliers toward both enhanced and reduced abundances. Regions with enhanced abundances have high ionization parameter, higher Hα luminosity, lower Hα velocity dispersion, younger star clusters, and associated molecular gas clouds showing higher molecular gas densities. This indicates recent star formation has locally enriched the material. Regions with reduced abundances show increased Hα velocity dispersions, suggestive of mixing introducing more pristine material. We observe subtle azimuthal variations in half of the sample, but cannot always cleanly associate this with the spiral pattern. Regions with enhanced and reduced abundances are found distributed throughout the disk, and in half of our galaxies we can identify subsections of spiral arms with clearly associated metallicity gradients. This suggests spiral arms play a role in organizing and mixing the interstellar medium.

This paper introduces a new method of generating 21 cm maps that is based on ideas from ray tracing and excursion sets. In this method, photons generated in each grid cell are computed using the excursion set ideas while their propagation is accounted for by ray tracing. The method requires the overdensity field over a grid as a starting point. Then the usual reionization parameters, minimum mass of collapsed halos (M_min), number of ionizing photons deposited in the intergalactic medium per collapsed baryon (n_ion), and ratio of ionization rate to recombination rate (represented through n_rec) are used. Thus, this is a hybrid method that utilizes the results of theoretically motivated excursion sets and combines them with the computationally intensive procedure of ray tracing. As the method integrates simple principles of both the approaches, it is expected to yield precise and fast estimates of the power spectrum on the scales of interest (0.1 Mpc⁻¹ ≲ k ≲ 1.0 Mpc⁻¹).

New infrared spectra of 33 Galactic carbon stars from FORCAST on SOFIA reveal strong connections between stellar pulsations and the dust and molecular chemistry in their circumstellar shells. A sharp boundary in overall dust content, which predominantly measures the amount of amorphous carbon, separates the semiregular and Mira variables, with the semiregulars showing little dust in their spectra and the Miras showing more. In semiregulars, the contribution from SiC dust increases rapidly as the overall dust content grows, but in Miras, the SiC dust feature grows weaker as more dust is added. A similar dichotomy is found with the absorption band from CS at ∼7.3 μm, which is generally limited to semiregular variables. Observationally, these differences make it straightforward to distinguish semiregular and Mira variables spectroscopically without the need for long-term photometric observations or knowledge of their distances. The rapid onset of strong SiC emission in Galactic carbon stars in semiregular variables points to a different dust-condensation process before strong pulsations take over. The break in the production of amorphous carbon between semiregulars and Miras seen in the Galactic sample is also evident in Magellanic carbon stars, linking strong pulsations in carbon stars to the strong mass-loss rates which will end their lives as stars across a wide range of metallicities.

We perform a validation study of the latest version of the Alfvén Wave Solar atmosphere Model (AWSoM) within the Space Weather Modeling Framework. To do so, we compare the simulation results of the model with a comprehensive suite of observations for Carrington rotations representative of the solar minimum conditions extending from the solar corona to the heliosphere up to the Earth. In the low corona (r < 1.25 ${\text{}}{R}_{\odot }$), we compare with EUV images from both Solar-Terrestrial Relations Observatory-A/EUVI and Solar Dynamics Observatory/Atmospheric Imaging Assembly and to three-dimensional (3D) tomographic reconstructions of the electron temperature and density based on these same data. We also compare the model to tomographic reconstructions of the electron density from Solar and Heliospheric Observatory/Large Angle and Spectrometric Coronagraph observations (2.55 < r < 6.0${\text{}}{R}_{\odot }$). In the heliosphere, we compare model predictions of solar wind speed with velocity reconstructions from InterPlanetary Scintillation observations. For comparison with observations near the Earth, we use OMNI data. Our results show that the improved AWSoM model performs well in quantitative agreement with the observations between the inner corona and 1 au. The model now reproduces the fast solar wind speed in the polar regions. Near the Earth, our model shows good agreement with observations of solar wind velocity, proton temperature, and density. AWSoM offers an extensive application to study the solar corona and larger heliosphere in concert with current and future solar missions as well as being well suited for space weather predictions.

We identify member stars of more than 90 open clusters in the LAMOST survey. With the method of Fang et al., the chromospheric activity (CA) indices, $\mathrm{log}{R}_{\mathrm{CaK}}^{{\prime} }$ for 1091 member stars in 82 open clusters and $\mathrm{log}{R}_{{\rm{H}}\alpha }^{{\prime} }$ for 1118 member stars in 83 open clusters, are calculated. The relations between the average $\mathrm{log}{R}_{\mathrm{CaK}}^{{\prime} }$, $\mathrm{log}{R}_{{\rm{H}}\alpha }^{{\prime} }$ in each open cluster and its age are investigated in different T_eff and [Fe/H] ranges. We find that CA starts to decrease slowly from log t = 6.70 to log t = 8.50, and then decreases rapidly until log t = 9.53. The trend becomes clearer for cooler stars. The quadratic functions between log R' and log t with 4000 K  < T_eff < 5500 K are constructed, which can be used to roughly estimate ages of field stars with accuracy about 40% for $\mathrm{log}{R}_{\mathrm{CaK}}^{{\prime} }$ and 60% for $\mathrm{log}{R}_{{\rm{H}}\alpha }^{{\prime} }$.

Lyα emission is widely used to detect and confirm high-redshift galaxies and characterize the evolution of the intergalactic medium (IGM). However, many galaxies do not display Lyα emission in typical spectroscopic observations, and intrinsic Lyα emitters represent a potentially biased set of high-redshift galaxies. In this work, we analyze a set of 703 galaxies at 2 ≲ z ≲ 3 with both Lyα spectroscopy and measurements of other rest-frame ultraviolet and optical properties in order to develop an empirical model for Lyα emission from galaxies and understand how the probability of Lyα emission depends on other observables. We consider several empirical proxies for the efficiency of Lyα photon production, as well as the subsequent escape of these photons through their local interstellar medium. We find that the equivalent width of metal-line absorption and the O3 ratio of rest-frame optical nebular lines are advantageous empirical proxies for Lyα escape and production, respectively. We develop a new quantity, ${X}_{\mathrm{LIS}}^{{\rm{O}}3}$, that combines these two properties into a single predictor of net Lyα emission, which we find describes ∼90% of the observed variance in Lyα equivalent width when accounting for our observational uncertainties. We also construct conditional probability distributions demonstrating that galaxy selection based on measurements of galaxy properties yield samples of galaxies with widely varying probabilities of net Lyα emission. The application of the empirical models and probability distributions described here may be used to infer the selection biases of current galaxy surveys and evaluate the significance of high-redshift Lyα (non)detections in studies of reionization and the IGM.

The MAMMOTH-I Nebula at redshift 2.3 is one of the largest known Lyα nebulae in the universe, spanning ∼440 kpc. Enormous Lyα nebulae like MAMMOTH-I typically trace the densest and most active regions of galaxy formation. Using sensitive low-surface-brightness observations of CO(1−0) with the Very Large Array, we trace the cold molecular gas in the inner 150 kpc of the MAMMOTH-I Nebula. CO is found in four regions that are associated with either galaxies or groups of galaxies that lie inside the nebula. In three of the regions, the CO stretches up to ∼30 kpc into the circumgalactic medium (CGM). In the centermost region, the CO has a very low velocity dispersion (FWHM_CO ∼ 85 km s⁻¹), indicating that this gas is dynamically cold. This dynamically cold gas coincides with diffuse rest-frame optical light in the CGM around a central group of galaxies, as discovered with the Hubble Space Telescope. We argue that this likely represents cooling of settled and enriched gas in the center of MAMMOTH-I. This implies that the dynamically cold gas in the CGM, rather than the obscured active galactic nucleus, marks the core of the potential well of this Lyα nebula. In total, the CO in the MAMMOTH-I Nebula traces a molecular gas mass of M_H2 ∼ 1.4(α_CO/3.6) × 10¹¹M_⊙, with roughly 50% of the CO(1−0) emission found in the CGM. Our results add to the increasing evidence that extended reservoirs of molecular gas exist in the CGM of massive high-z galaxies and protoclusters.

Only four star clusters are known within ∼100 pc of Earth. Of these, the χ¹ For cluster has barely been studied. We use the Gaia DR2 catalog and other published data to establish the cluster membership, structure, and age. The age of and distance to the cluster are ∼40 Myr and 104 pc, respectively. A remarkable, unprecedented aspect of the cluster is the large percentage of M-type stars with warm excess infrared emission due to orbiting dust grains—these stars lie in an annulus that straddles the tidal radius of the cluster. The χ¹ For cluster appears to be closely related to two extensive, previously known, groups of comoving, coeval stars (the Tucana-Horologium and Columba Associations) that are spread over much of the southern sky. While Tuc-Hor and χ¹ For are comoving and coeval, the difference in the frequency of their warm dusty debris disks at M-type stars could hardly be more dramatic.

We present ALMA CO (1−0) observations toward the dust lane of the nearest elliptical and radio galaxy, NGC 5128 (Centaurus A), with high angular resolution (∼1'', or 18 pc), including information from large to small spatial scales and total flux. We find a total molecular gas mass of 1.6 × 10⁹M_⊙ and reveal the presence of filamentary components more extended than previously seen, up to a radius of 4 kpc. We find that the global star formation rate is ∼1 M_⊙ yr⁻¹, which yields a star formation efficiency (SFE) of 0.6 Gyr⁻¹ (depletion time τ = 1.5 Gyr), similar to those in disk galaxies. We show the most detailed view to date (40 pc resolution) of the relation between molecular gas and star formation within the stellar component of an elliptical galaxy, from a scale of several kiloparsecs to the circumnuclear region close to the powerful radio jet. Although on average the SFEs are similar to those of spiral galaxies, the circumnuclear disk (CND) presents SFEs of 0.3 Gyr⁻¹, lower by a factor of 4 than the outer disk. The low SFE in the CND is in contrast to the high SFEs found in the literature for the circumnuclear regions of some nearby disk galaxies with nuclear activity, probably as a result of larger shear motions and longer active galactic nucleus feedback. The higher SFEs in the outer disk suggest that only central molecular gas or filaments with sufficient density and strong shear motions will remain in ∼1 Gyr, which will later result in the compact molecular distributions and low SFEs usually seen in other giant ellipticals with cold gas.

We address the spatial scale, ionization structure, mass, and metal content of gas at the Milky Way disk–halo interface detected as absorption in the foreground of seven closely spaced, high-latitude halo blue horizontal branch stars with heights z = 3–14 kpc. We detect transitions that trace multiple ionization states (e.g., Ca ii, Fe ii, Si iv, C iv) with column densities that remain constant with height from the disk, indicating that the gas most likely lies within z < 3.4 kpc. The intermediate ionization state gas traced by C iv and Si iv is strongly correlated over the full range of transverse separations probed by our sight lines, indicating large, coherent structures greater than 1 kpc in size. The low ionization state material traced by Ca ii and Fe ii does not exhibit a correlation with either N_{H i} or transverse separation, implying cloudlets or clumpiness on scales less than 10 pc. We find that the observed ratio log(N_{Si iv}/N_{C iv}), with a median value of −0.69 ± 0.04, is sensitive to the total carbon content of the ionized gas under the assumption of either photoionization or collisional ionization. The only self-consistent solution for photoionized gas requires that Si be depleted onto dust by 0.35 dex relative to the solar Si/C ratio, similar to the level of Si depletion in DLAs and in the Milky Way interstellar medium. The allowed range of values for the areal mass infall rate of warm, ionized gas at the disk−halo interface is 0.0003 < dM_gas/dtdA [M_⊙ kpc⁻² yr⁻¹] <0.006. Our data support a physical scenario in which the Milky Way is fed by complex, multiphase processes at its disk−halo interface that involve kiloparsec-scale ionized envelopes or streams containing parsec-scale, cool clumps.

We report the discovery of SDSS J0849+1114 as the first known triple Type 2 Seyfert nucleus. It represents three active black holes that are identified from new spatially resolved optical slit spectroscopy using the Dual Imaging Spectrograph on the 3.5 m telescope at the Apache Point Observatory. We also present new complementary observations including the Hubble Space Telescope Wide Field Camera 3 U- and Y-band imaging, Chandra Advanced CCD Imaging Spectrometer S-array X-ray 0.5–8 keV imaging spectroscopy, and NSF Karl G. Jansky Very Large Array radio 9.0 GHz imaging in its most extended A configuration. These comprehensive multiwavelength observations, when combined together, strongly suggest that all three nuclei are active galactic nuclei. While they are now still at kiloparsec-scale separations, where the host-galaxy gravitational potential dominates, the black holes may evolve into a bound triple system in ≲2 Gyr. These triple merger systems may explain the overly massive stellar cores that have been observed in some elliptical galaxies such as M87, which are expected to be unique gravitational wave sources. Similar systems may be more common in the early universe, when galaxy mergers are thought to have been more frequent.

The Hubble Space Telescope (HST) UV Legacy Survey of Galactic Globular Clusters (GCs) has investigated multiple stellar populations by means of the "chromosome map" (ChM) diagnostic tool that maximizes the separation between stars with different chemical compositions. One of the most challenging features revealed by ChM analysis is the apparent inhomogeneity among stars belonging to the first population, a phenomenon largely attributed to He variations. However, this explanation is not supported by uniformity in the p-capture elements of these stars. The HST survey has revealed that the GC NGC 3201 shows exceptionally wide coverage in the ${{\rm{\Delta }}}_{{\rm{F}}275{\rm{W}},{\rm{F}}814{\rm{W}}}$ parameter of the ChM. We present a chemical abundance analysis of 24 elements in 18 giants belonging to the first population of this GC and having a wide range in ${{\rm{\Delta }}}_{{\rm{F}}275{\rm{W}},{\rm{F}}814{\rm{W}}}$. As far as the p-capture elements are concerned, the chemical abundances are typical of first-generation (1G) stars, as expected from the location of our targets in the ChM. Based on radial velocities and chemical abundance arguments, we find that the three stars with the lowest ${{\rm{\Delta }}}_{{\rm{F}}275{\rm{W}},{\rm{F}}814{\rm{W}}}$ values are binary candidates. This suggests that at least those stars could be explained with binarity. These results are consistent with evidence inferred from multiband photometry that evolved blue stragglers (BSs) populate the bluest part of the 1G sequence in the ChM. The remaining 15 spectroscopic targets show a small range in the overall metallicity by ∼0.10 dex, with stars at higher ${{\rm{\Delta }}}_{{\rm{F}}275{\rm{W}},{\rm{F}}814{\rm{W}}}$ values having higher absolute abundances. We suggest that a small variation in metals and binarity governs the color spread of the 1G in the ChM and that evolved BSs contribute to the bluest tail of the 1G sequence.

Large low-surface-brightness galaxies have recently been found to be abundant in nearby galaxy clusters. In this paper, we investigate these ultra-diffuse galaxies (UDGs) in the six Hubble Frontier Fields galaxy clusters: A2744, MACS J0416.1−2403, MACS J0717.5+3745, MACS J1149.5+2223, AS1063, and A370. These are the most massive (1–3 × 10¹⁵M_⊙) and distant (0.308 < z < 0.545) systems in which this class of galaxy has yet been discovered. We estimate that the clusters host of the order of ∼200–1400 UDGs inside the virial radius (R₂₀₀), consistent with the UDG abundance–halo-mass relation found in the local universe, and suggest that UDGs may be formed in clusters. Within each cluster, however, we find that UDGs are not evenly distributed. Instead their projected spatial distributions are lopsided, and they are deficient in the regions of highest mass density as traced by gravitational lensing. While the deficiency of UDGs in central regions is not surprising, the lopsidedness is puzzling. The UDGs, and their lopsided spatial distributions, may be associated with known substructures late in their infall into the clusters, meaning that we find evidence both for formation of UDGs in clusters and for UDGs falling into clusters. We also investigate the ultra-compact dwarfs (UCDs) residing in the clusters, and find that the spatial distributions of UDGs and UCDs appear anticorrelated. Around 15% of UDGs exhibit either compact nuclei or nearby point sources. Taken together, these observations provide additional evidence for a picture in which at least some UDGs are destroyed in dense cluster environments and leave behind a residue of UCDs.

We present a new three-dimensional map of dust reddening, based on Gaia parallaxes and stellar photometry from Pan-STARRS 1 and 2MASS. This map covers the sky north of a decl. of −30°, out to a distance of a few kiloparsecs. This new map contains three major improvements over our previous work. First, the inclusion of Gaia parallaxes dramatically improves distance estimates to nearby stars. Second, we incorporate a spatial prior that correlates the dust density across nearby sightlines. This produces a smoother map, with more isotropic clouds and smaller distance uncertainties, particularly to clouds within the nearest kiloparsec. Third, we infer the dust density with a distance resolution that is four times finer than in our previous work, to accommodate the improvements in signal-to-noise enabled by the other improvements. As part of this work, we infer the distances, reddenings, and types of 799 million stars. (Our 3D dust map can be accessed at doi:10.7910/DVN/2EJ9TX or through the Python package dustmaps, while our catalog of stellar parameters can be accessed at doi:10.7910/DVN/AV9GXO. More information about the map, as well as an interactive viewer, can be found at argonaut.skymaps.info.) We obtain typical reddening uncertainties that are ∼30% smaller than those reported in the Gaia DR2 catalog, reflecting the greater number of photometric passbands that enter into our analysis.

Dark-matter-only simulations predict that dark matter halos have steep, cuspy inner density profiles, while observations of dwarf galaxies find a range of inner slopes that are often much shallower. There is debate whether this discrepancy can be explained by baryonic feedback or if it may require modified dark matter models. In Paper I of this series, we obtained high-resolution integral field Hα observations for 26 dwarf galaxies with M_* = 10^8.1−10^9.7$\,{\text{}}{M}_{\odot }$. We derived rotation curves from our observations, which we use here to construct mass models. We model the total mass distribution as the sum of a generalized Navarro–Frenk–White (NFW) dark matter halo and the stellar and gaseous components. Our analysis of the slope of the dark matter density profile focuses on the inner 300–800 pc, chosen based on the resolution of our data and the region resolved by modern hydrodynamical simulations. The inner slope measured using ionized and molecular gas tracers is consistent, and it is additionally robust to the choice of stellar mass-to-light ratio. We find a range of dark matter profiles, including both cored and cuspy slopes, with an average of ${\rho }_{\mathrm{DM}}\sim {r}^{-0.74\pm 0.07}$, shallower than the NFW profile, but steeper than those typically observed for lower-mass galaxies with M_* ∼ 10^7.5$\,{\text{}}{M}_{\odot }$. Simulations that reproduce the observed slopes in those lower-mass galaxies also produce slopes that are too shallow for galaxies in our mass range. We therefore conclude that supernova feedback models do not yet provide a fully satisfactory explanation for the observed trend in dark matter slopes.

The existence of partially conserved enstrophy-like quantities is conjectured to cause inverse energy transfers to develop embedded in magnetohydrodynamical (MHD) turbulence, in analogy to the influence of enstrophy in two-dimensional nonconducting turbulence. By decomposing the velocity and magnetic fields in spectral space onto helical modes, we identify subsets of three-wave (triad) interactions conserving two new enstrophy-like quantities that can be mapped to triad interactions recently identified with facilitating large-scale α-type dynamo action and the inverse transfer of magnetic helicity. Due to their dependence on interaction scale locality, invariants suggest that the inverse transfer of magnetic helicity might be facilitated by both local- and nonlocal-scale interactions, and is a process more local than the α-dynamo. We test the predicted embedded (partial) energy fluxes by constructing a shell model (reduced wave-space model) of the minimal set of triad interactions (MTI) required to conserve the ideal MHD invariants. Numerically simulated MTIs demonstrate that, for a range of forcing configurations, the partial invariants are, with some exceptions, indeed useful for understanding the embedded contributions to the total spectral energy flux. Furthermore, we demonstrate that strictly inverse energy transfers may develop if enstrophy-like conserving interactions are favored, a mechanism recently attributed to the energy cascade reversals found in nonconducting three-dimensional turbulence subject to strong rotation or confinement. The presented results have implications for the understanding of the physical mechanisms behind large-scale dynamo action and the inverse transfer of magnetic helicity, processes thought to be central to large-scale magnetic structure formation.

The expansion of hot electrons in flaring magnetic loops is crucial to understanding the dynamics of solar flares. In this paper we investigate, for the first time, the transport of hot electrons in a magnetic mirror field based on a 1D particle-in-cell simulation model. The hot electrons with small pitch angles transport into the cold plasma, which leads to the generation of Langmuir waves in the cold plasma and ion acoustic waves in the hot plasma. The large pitch angle electrons can be confined by the magnetic mirror, resulting in the different evolution timescale between electron parallel and perpendicular temperatures. This will cause the formation of electron temperature anisotropy, which then generates the whistler waves near the interface between hot electrons and cold electrons. The whistler waves can scatter the large pitch angle electrons to smaller value through the cyclotron resonance, leading to electrons escaping from the hot region. These results indicate that the whistler waves may play an important role in the transport of electrons in flaring magnetic loops. The findings from this study provide some new insights to understand the electron dynamics of solar flares.

The number of classes of gamma-ray bursts (GRBs), besides the well-established short and long ones, remains a debatable issue. It was already shown, however, that when invoking skewed distributions, the $\mathrm{log}{T}_{90}$ and $\mathrm{log}{T}_{90}-\mathrm{log}{H}_{32}$ spaces are adequately modeled with mixtures of only two such components, implying two GRB types. Herein, a comprehensive multivariate analysis of several multidimensional parameter spaces is conducted for the BATSE sample of GRBs, with the usage of skewed distributions. It is found that the number of extracted components varies between the examined parameter sets, and ranges from 2 to 4, with higher-dimensional spaces allowing for more classes. Monte Carlo testing implies that these additional components are likely to be artifacts owing to the finiteness of the data and to be a result of examining a particular realization of the data as a random sample, resulting in spurious identifications.

We present the particular case of the Stephani solution for shear-free perfect fluid with uniform energy density and nonuniform pressure. Such models appeared as possible alternative to the consideration of the exotic forms of matter like dark energy that would cause the acceleration of universe expansion. These models are characterized by the spatial curvature, depending on time. We analyze the properties of the cosmological model obtained on the basis of exact solution of the Stephani class, and adapt it to the recent observational data. The spatial geometry of the model is investigated. We show that despite possible singularities, the model can describe the current stage of the universe's evolution.

Using the Hα data from the New Vacuum Solar Telescope at the Fuxian Solar Observatory together with multiwavelength images and magnetograms obtained by the Solar Dynamics Observatory, we study the detailed process of three homologous confined flares in active region NOAA 11861 on 2013 October 12. All of the three flares occurred at the same location, with similar morphologies and comparable classes. Through analyzing the evolution of magnetic field and flow field, we found an emergence of magnetic flux and a strong shearing motion between two opposite polarities near the following sunspot. The magnetic flux and the average transverse field strength exhibited a decrease before each eruption and reached the lowest point at the onset of each eruption. By calculating the shearing and the emergence energy in the photosphere, we found that the integral of energy injected from the photosphere, for a few hours, could provide enough energy for the flares. The reconnection between different loops was observed in Hα images during the occurrence of each flare. These results suggest that the emerging magnetic flux and the shearing motion in the photosphere can inject the energy to the sheared magnetic loops and the energy was finally released via magnetic reconnection to power the solar flares.

Model predictions of X-ray burst ashes and light curves depend on the composition of the material accreted from the companion star, in particular the abundance of CNO elements. It has previously been pointed out that spallation in the atmosphere of the accreting neutron star can destroy heavy elements efficiently. In this work we study this spallation using a realistic reaction network that follows the complete spallation cascade and takes into account not only destruction, but also production of elements by the spallation of heavier species. We find an increased survival probability of heavier elements compared to previous studies, resulting in significantly higher CNO abundances. We provide resulting compositions as a function of accretion rate, and explore their impact on 1D multi-zone X-ray burst models. We find significant changes in the composition of the burst ashes, which will affect the thermal and compositional structure of accreted neutron star crusts.

We present the X-ray timing and spectral analysis of the new Galactic X-ray transient Swift J1658.2–4242 observed with the Large Area X-ray Proportional Counter and Soft X-ray Telescope instruments on board Astrosat. We detect prominent C-type quasi-periodic oscillations (QPOs) of frequencies varying from ∼1.5 to ∼6.6 Hz along with distinct second harmonics and subharmonics. The QPO detected at ∼1.56 Hz drifts to a higher centroid frequency of ∼1.74 in the course of the observation, while the QPO detected at ∼6.6 Hz disappeared during hard flarings. The fractional rms at the QPO and the subharmonic frequencies increases with photon energy, while at the second harmonic frequencies the rms seems to be constant. In addition, we have observed soft time lag at QPO and subharmonic frequencies up to a timescale of ∼35 ms; however, at the second harmonic frequencies there is weak/zero time lag. We attempt spectral modeling of the broadband data in the 0.7–25 keV band using the doubly absorbed disk plus thermal Comptonization model. Based on the spectral and timing properties, we identified the source to be in the hard-intermediate state of black hole X-ray binaries. To quantitatively fit the energy- and frequency-dependent fractional rms and time lag, we use a single-zone fluctuation propagation model and discuss our results in the context of that model.

We investigate energetic electron transport in a meandering interplanetary magnetic field under the scatter-free regime. The meandering magnetic field is adopted from the Giacalone model in which a single parameter V_rms is used to characterize how the interplanetary magnetic field deviates from the Parker field. The trajectories of energetic electrons are followed in this meandering field using test particle simulations. Ten thousand electrons are injected in the ecliptic plane and the path length distributions are obtained at distances 0.2, 0.5, 1.0, 2.0, and 3.0 au from the Sun for five different V_rms, 0.3, 0.6, 1.0, 1.5, 2.0, and 2.5 km s⁻¹. By generating 10,000 different realizations of the meandering field line, we also obtain the path length distribution of the field lines. Our simulations show that the path length distributions of the electrons and that of the field lines are different and the difference increases with V_rms. When the V_rms approaches zero, the field lines approach the Parker field, and the differences between particle path lengths and field path lengths are small but nonzero due to the gradient and curvature drifts. The path lengths for 1 MeV electrons do not differ much from those for 100 MeV electrons. Our results of the distribution of electron path length can be compared to the observations of Zhao et al. to set constraints on V_rms. We also calculate both the longitudinal and latitudinal displacements from the source when electrons arrive at 1 au. This provides some basis for understanding simultaneous observations of impulsive events made at multiple spacecraft.

We simulate a coronal mass ejection using a three-dimensional magnetohydrodynamic code that includes coronal heating, thermal conduction, and radiative cooling in the energy equation. The magnetic flux distribution at 1 R_s is produced by a localized subsurface dipole superimposed on a global dipole field, mimicking the presence of an active region within the global corona. Transverse electric fields are applied near the polarity inversion line to introduce a transverse magnetic field, followed by the imposition of a converging flow to form and destabilize a flux rope, producing an eruption. We examine the quantities responsible for plasma heating and cooling during the eruption, including thermal conduction, radiation, adiabatic effects, coronal heating, and ohmic heating. We find that ohmic heating is an important contributor to hot temperatures in the current sheet region early in the eruption, but in the late phase, adiabatic compression plays an important role in heating the plasma there. Thermal conduction also plays an important role in the transport of thermal energy away from the current sheet region throughout the reconnection process, producing a "thermal halo" and widening the region of high temperatures. We simulate emission from solar telescopes for this eruption and find that there is evidence for emission from heated plasma above the flare loops late in the eruption, when the adiabatic heating is the dominant heating term. These results provide an explanation for hot supra-arcade plasma sheets that are often observed in X-rays and extreme ultraviolet wavelengths during the decay phase of large flares.

Blazars, in particular the subclass of high synchrotron peaked active galactic nuclei are among the main targets for the present generation of Imaging Atmospheric Cerenkov Telescopes (IACTs), and they will remain of great importance for very high-energy γ-ray science in the era of the Cerenkov Telescope Array (CTA). Observations by IACTs, which have relatively small fields of view (∼few degrees), are limited by viewing conditions; therefore, it is important to select the most promising targets to increase the number of detections. The aim of this paper is to search for unclassified blazars among known γ-ray sources from the Fermi Large Area Telescope (LAT) third source catalog that are likely detectable with IACTs or CTA. We use an artificial neural network algorithm and updated analysis of Fermi-LAT data. We found 80 γ-ray source candidates, and for the highest-confidence candidates, we calculate their potential detectability with IACTs and CTA based on an extrapolation of their energy spectra. Follow-up observations of our source candidates could significantly increase the current TeV source population sample and ultimately confirm the efficiency of our algorithm to select TeV sources.

We present resolved [C i] line intensities of 18 nearby galaxies observed with the SPIRE FTS spectrometer on the Herschel Space Observatory. We use these data along with resolved CO line intensities from J_up = 1 to 7 to interpret what phase of the interstellar medium the [C i] lines trace within typical local galaxies. A tight, linear relation is found between the intensities of the CO(4–3) and [C i](2–1) lines; we hypothesize this is due to the similar upper level temperature of these two lines. We modeled the [C i] and CO line emission using large-velocity gradient models combined with an empirical template. According to this modeling, the [C i](1–0) line is clearly dominated by the low-excitation component. We determine [C i] to molecular mass conversion factors for both the [C i](1–0) and [C i](2–1) lines, with mean values of α_{[C i](1−0)} = 7.3 M_⊙ K⁻¹ km⁻¹ s pc⁻² and α_{[C i](2−1)} = 34 M_⊙ K⁻¹ km⁻¹ s pc⁻² with logarithmic root-mean-square spreads of 0.20 and 0.32 dex, respectively. The similar spread of ${\alpha }_{[{\rm{C}}{\rm{I}}](1\mbox{--}0)}$ to ${\alpha }_{\mathrm{CO}}$ (derived using the CO(2–1) line) suggests that [C i](1–0) may be just as good a tracer of cold molecular gas as CO(2–1) in galaxies of this type. On the other hand, the wider spread of α_{[C i](2−1)} and the tight relation found between [C i](2–1) and CO(4–3) suggest that much of the [C i](2–1) emission may originate in warmer molecular gas.

We analyze a set of 89 type Ia supernovae (SNe Ia) that have both optical and near-infrared (NIR) photometry to derive distances and construct low-redshift (z ≤ 0.04) Hubble diagrams. We construct mean light curve (LC) templates using a hierarchical Bayesian model. We explore both Gaussian process (GP) and template methods for fitting the LCs and estimating distances, while including peculiar-velocity and photometric uncertainties. For the 56 SNe Ia with both optical and NIR observations near maximum light, the GP method yields a NIR-only Hubble-diagram with a root mean square (rms) of $0.117\,\pm \,0.014$ mag when referenced to the NIR maxima. For each NIR band, a comparable GP method rms is obtained when referencing to NIR-max or B-max. Using NIR LC templates referenced to B-max yields a larger rms value of $0.138\,\pm \,0.014$ mag. Fitting the corresponding optical data using standard LC fitters that use LC shape and color corrections yields larger rms values of 0.179 ± 0.018 mag with SALT2 and $0.174\,\pm \,0.021$ mag with SNooPy. Applying our GP method to subsets of SNe Ia NIR LCs at NIR maximum light, even without corrections for LC shape, color, or host-galaxy dust reddening, provides smaller rms in the inferred distances, at the ∼2.3–4.1σ level, than standard optical methods that correct for those effects. Our ongoing RAISIN program on the Hubble Space Telescope will exploit this promising infrared approach to limit systematic errors when measuring the expansion history of the universe in order to constrain dark energy.