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With the upcoming launch of space telescopes dedicated to the study of exoplanets, the Atmospheric Remote-Sensing Infrared Exoplanet Large-survey (ARIEL) and the James Webb Space Telescope (JWST), a new era is opening in exoplanetary atmospheric explorations. However, especially in relatively cold planets around later-type stars, photochemical hazes and clouds may mask the composition of the lower part of the atmosphere, making it difficult to detect any chemical species in the troposphere or understand whether there is a surface or not. This issue is particularly exacerbated if the goal is to study the habitability of said exoplanets and search for biosignatures. This work combines innovative laboratory experiments, chemical modeling, and simulated observations at ARIEL and JWST resolutions. We focus on the signatures of molecular ions that can be found in upper atmospheres above cloud decks. Our results suggest that ${{\rm{H}}}_{3}^{+}$ along with H₃O⁺ could be detected in the observational spectra of sub-Neptunes based on a realistic mixing ratio assumption. This new parametric set may help to distinguish super-Earths with a thin atmosphere from H₂-dominated sub-Neptunes to address the critical question of whether a low-gravity planet around a low-mass active star is able to retain its volatile components. These ions may also constitute potential tracers to certain molecules of interest, such as H₂O or O₂, to probe the habitability of exoplanets. Their detection will be an enthralling challenge for the future JWST and ARIEL telescopes.

We present chemical abundances of red giant branch (RGB) stars in the dwarf spheroidal (dSph) satellite system of Andromeda (M31), using spectral synthesis of medium-resolution (R ∼ 6000) spectra obtained with the Keck II telescope and Deep Imaging Multi-Object Spectrometer spectrograph via the Spectroscopic and Photometric Landscape of Andromeda's Stellar Halo survey. We coadd stars according to their similarity in photometric metallicity or effective temperature to obtain a signal-to-noise ratio (S/N) high enough to measure average [Fe/H] and [α/Fe] abundances. We validate our method using high S/N spectra of RGB stars in Milky Way globular clusters, as well as deep observations for a subset of the M31 dSphs in our sample. For this set of validation coadds, we compare the weighted average abundance of the individual stars with the abundance determined from the coadd. We present individual and coadded measurements of [Fe/H] and [α/Fe] for stars in 10 M31 dSphs, including the first [α/Fe] measurements for And IX, XIV, XV, and XVIII. These fainter, less massive dSphs show declining [α/Fe] relative to [Fe/H], implying an extended star formation history (SFH). In addition, these dSphs also follow the same mass–metallicity relation found in other Local Group satellites. The conclusions we infer from coadded spectra agree with those from previous measurements in brighter M31 dSphs with individual abundance measurements, as well as conclusions from photometric studies. These abundances greatly increase the number of spectroscopic measurements of the chemical composition of M31's less massive dwarf satellites, which are crucial to understanding their SFH and interaction with the M31 system.

We analyze archival Chandra X-ray Observatory observations of Jupiter to search for emission from the Galilean moons. X-ray emission has previously been reported from Io and Europa using a subset of these data. We confirm this detection, and marginally detect X-ray emission from both Ganymede and Callisto as well. The X-ray spectrum of Europa is strongly peaked around the neutral oxygen fluorescence line (525 eV), while Io's has peaks at both oxygen and sulfur (2308 eV) plus a broad continuum between 350 and 5000 eV. Ganymede's spectrum is similar to Io's, but without the sulfur peak. A few events, mostly clustered around the oxygen line, are detected from Callisto. Using measurements by the Galileo mission of the specific intensity of ambient protons and electrons, we model the X-ray spectra and flux of the moons from two processes: particle-induced X-ray emission (PIXE) from the impact of energetic protons and X-ray emission from electron bremsstrahlung. With uncertainties of a factor of a few, the electron bremsstrahlung and PIXE models overestimate the X-ray flux from Europa, preventing us from making a definitive statement about the origin of the X-ray emission. The PIXE model of Io predicts emission lines at O and S similar to those observed, but underestimates their flux by nearly two orders of magnitude. Based on this discrepancy in the PIXE flux, combined with the detected broadband continuum in the spectrum, we conclude that the X-ray emission from Io is due to electron bremsstrahlung. Likewise, because of Ganymede's broad continuum, we tentatively conclude that its X-ray emission is also due to electron bremsstrahlung. Callisto is too faint in the X-rays to draw any conclusion. Obtaining in situ X-ray observations of the moons would provide a direct measurement of their elemental composition.

The recurrent nova (RN) V3890 Sgr was observed during the seventh day after the onset of its most recent outburst, with the Chandra ACIS-S camera and High Energy Transmission Gratings. A rich emission line spectrum was detected, due to transitions of Fe-L and K-shell ions ranging from neon to iron. The measured absorbed flux is ≈10⁻¹⁰ erg cm⁻² s⁻¹ in the 1.4–15 Å range (0.77–8.86 keV). The line profiles are asymmetric, blueshifted, and skewed toward the blue side, as if the ejecta moving toward us are less absorbed than the receding ejecta. The full width at half-maximum of most emission lines is 1000–1200 km s⁻¹, with some extended blue wings. The spectrum is thermal and consistent with a plasma in collisional ionization equilibrium with column density 1.3 × 10²² cm⁻² and at least two components at temperatures of about 1 and 4 keV, possibly a forward and a reverse shock, or regions with differently mixed ejecta and a red giant wind. The spectrum is remarkably similar to the symbiotic RNe V745 Sco and RS Oph, but we cannot distinguish whether the shocks occurred at a distance of a few au from the red giant, or near the giant's photosphere, in a high-density medium containing only a low mass. The ratios of the flux in lines of aluminum, magnesium, and neon relative to the flux in lines of silicon and iron probably indicate a carbon–oxygen white dwarf.

We report the detection of CO(J = 2 → 1) emission from three massive dusty starburst galaxies at z > 5 through molecular line scans in the NSF's Karl G. Jansky Very Large Array (VLA) CO Luminosity Density at High Redshift (COLDz) survey. Redshifts for two of the sources, HDF 850.1 (z = 5.183) and AzTEC-3 (z = 5.298), were previously known. We revise a previous redshift estimate for the third source GN10 (z = 5.303), which we have independently confirmed through detections of CO J = 1 → 0, 5 → 4, 6 → 5, and [C ii] 158 μm emission with the VLA and the NOrthern Extended Milllimeter Array. We find that two currently independently confirmed CO sources in COLDz are "optically dark", and that three of them are dust-obscured galaxies at z > 5. Given our survey area of ∼60 arcmin², our results appear to imply a ∼6–55 times higher space density of such distant dusty systems within the first billion years after the Big Bang than previously thought. At least two of these z > 5 galaxies show star formation rate surface densities consistent with so-called "maximum" starbursts, but we find significant differences in CO excitation between them. This result may suggest that different fractions of the massive gas reservoirs are located in the dense, star-forming nuclear regions—consistent with the more extended sizes of the [C ii] emission compared to the dust continuum and higher [C ii]-to-far-infrared luminosity ratios in those galaxies with lower gas excitation. We thus find substantial variations in the conditions for star formation between z > 5 dusty starbursts, which typically have dust temperatures that are ∼57% ± 25% warmer than starbursts at z = 2–3 due to their enhanced star formation activity.

Mixing above the proto-neutron star is believed to play an important role in the supernova engine, and this mixing results in a supernova explosion with asymmetries. Elements produced in the innermost ejecta, e.g., ⁵⁶Ni and ⁴⁴Ti, provide a clean probe of this engine. The production of ⁴⁴Ti is particularly sensitive to the exact production pathway and, by understanding the available pathways, we can use ⁴⁴Ti to probe the supernova engine. Using thermodynamic trajectories from a three-dimensional supernova explosion model, we review the production of these elements and the structures expected to form under the "convective-engine" paradigm behind supernovae. We compare our results to recent X-ray and γ-ray observations of the Cassiopeia A supernova remnant.

Weakly collisional space plasmas are rarely in local thermal equilibrium and often exhibit non-Maxwellian electron and ion velocity distributions that lead to the growth of microinstabilities—that is, enhanced electric and magnetic fields at relatively short wavelengths. These instabilities play an active role in the evolution of space plasmas, as does ubiquitous broadband turbulence induced by turbulent structures. This study compares certain properties of a 2.5-dimensional particle-in-cell (PIC) simulation for the forward cascade of Alfvénic turbulence in a collisionless plasma against the same properties of turbulence observed by the Magnetospheric Multiscale Mission spacecraft in the terrestrial magnetosheath. The PIC simulation is of decaying turbulence that develops both coherent structures and anisotropic ion velocity distributions with the potential to drive kinetic scale instabilities. The uniform background magnetic field points perpendicular to the plane of the simulation. Growth rates are computed from linear theory using the ion temperature anisotropies and ion beta values for both the simulation and the observations. Both the simulation and the observations show that strong anisotropies and growth rates occur highly intermittently in the plasma, and the simulation further shows that such anisotropies preferentially occur near current sheets. This suggests that, though microinstabilities may affect the plasma globally, they act locally and develop in response to extreme temperature anisotropies generated by turbulent structures. Further studies will be necessary to understand why there is an apparent correlation between linear instability theory and strongly intermittent turbulence.

With an emphasis on improving the fidelity even in super-resolution regimes, new imaging techniques have been intensively developed over the last several years, which may provide substantial improvements to the interferometric observation of protoplanetary disks. In this study, sparse modeling (SpM) is applied for the first time to observational data sets taken by the Atacama Large Millimeter/submillimeter Array (ALMA). The two data sets used in this study were taken independently using different array configurations at Band 7 (330 GHz), targeting the protoplanetary disk around HD 142527: one in the shorter-baseline array configuration (∼430 m), and the other in the longer-baseline array configuration (∼1570 m). The image resolutions reconstructed from the two data sets are different by a factor of ∼3. We confirm that the previously known disk structures appear on the images produced by both SpM and CLEAN at the standard beam size. The image reconstructed from the shorter-baseline data using the SpM matches that obtained with the longer-baseline data using the CLEAN, achieving a super-resolution image from which a structure finer than the beam size can be reproduced. Our results demonstrate that ongoing intensive development in the SpM imaging technique is beneficial to imaging with ALMA.

A galaxy–galaxy merger and the subsequent triggering of starburst activity are fundamental processes linked to the morphological transformation of galaxies and the evolution of star formation across the history of the universe. Both nuclear and disk-wide starbursts are assumed to occur during the merger process. However, quantifying both nuclear and disk-wide star formation activity is nontrivial because the nuclear starburst is dusty in the most active merging starburst galaxies. This paper presents a new approach to this problem: combining hydrogen recombination lines in optical, millimeter, and free–free emission. Using NGC 3256 as a case study, Hβ, H40α, and free–free emissions are investigated using the Multi Unit Spectroscopic Explorer at the Very Large Telescope of the European Southern Observatory (MUSE) and the Atacama Large Millimeter/submillimeter Array (ALMA). The Hβ image obtained by MUSE identifies star-forming regions outside the nuclear regions, suggesting a disk-wide starburst. In contrast, the H40α image obtained by ALMA identifies a nuclear starburst where optical lines are undetected due to dust extinction (A_V ∼ 25). Combining both MUSE and ALMA observations, we conclude that the total star formation rate (SFR) is 49 ± 2 M_⊙ yr⁻¹ and the contributions from nuclear and disk-wide starbursts are ∼34% and ∼66%, respectively. This suggests the dominance of disk-wide star formation in NGC 3256. In addition, pixel-by-pixel analyses for disk-wide star-forming regions suggest that shock gas tracers (e.g., CH₃OH) are enhanced where gas depletion time (τ_gas = M_gas/SFR) is long. This possibly means that merger-induced shocks regulate disk-wide star formation activities.

After hydrogen, oxygen, and carbon, nitrogen is one of the most chemically active species in the interstellar medium. Nitrogen-bearing molecules are very important as they are actively involved in the formation of biomolecules. Therefore, it is essential to look for nitrogen-bearing species in various astrophysical sources, specifically around high-mass star-forming regions where the evolutionary history is comparatively poorly understood. In this paper, we report on the observation of three potential prebiotic molecules, namely, isocyanic acid (HNCO), formamide (NH₂CHO), and methyl isocyanate (CH₃NCO), which contain peptide-like bonds (–NH–C(=O)–) in a hot molecular core, G10.47 + 0.03 (hereafter, G10). Along with the identification of these three complex nitrogen-bearing species, we speculate on their spatial distribution in the source and discuss their possible formation pathways under such conditions. A rotational diagram method under local thermodynamic equilibrium has been employed to estimate the excitation temperature and the column density of the observed species. The Markov Chain Monte Carlo method was used to obtain the best-suited physical parameters of G10 as well as line properties of some species. We also determined the hydrogen column density and the optical depth for a different continuum observed in various frequency ranges. Finally, based on these observational results, we have constructed a chemical model to explain the observational findings. We found that HNCO, NH₂CHO, and CH₃NCO are chemically linked with each other.

A laboratory emission spectrum of TiO in the visible and near-infrared regions (476–1176 nm) has been calibrated and corrected. High-resolution experimental absorption cross sections for TiO with natural isotopic abundance are provided at a temperature of about 2300 K. These cross sections have been compared with those derived from the ExoMol line list. The experimental cross sections can be used directly as a template for cross correlation TiO detection in hot Jupiter exoplanets.

We report the first APOGEE metallicities and α-element abundances measured for 3600 red giant stars spanning a large radial range of both the Large (LMC) and Small Magellanic Clouds, the largest Milky Way (MW) dwarf galaxies. Our sample is an order of magnitude larger than that of previous studies and extends to much larger radial distances. These are the first results presented that make use of the newly installed southern APOGEE instrument on the du Pont telescope at Las Campanas Observatory. Our unbiased sample of the LMC spans a large range in metallicity, from [Fe/H] = −0.2 to very metal-poor stars with [Fe/H] ≈ −2.5, the most metal-poor Magellanic Cloud (MC) stars detected to date. The LMC [α/Fe]–[Fe/H] distribution is very flat over a large metallicity range but rises by ∼0.1 dex at −1.0 < [Fe/H] ≲ −0.5. We interpret this as a sign of the known recent increase in MC star formation activity and are able to reproduce the pattern with a chemical evolution model that includes a recent "starburst." At the metal-poor end, we capture the increase of [α/Fe] with decreasing [Fe/H] and constrain the "α-knee" to [Fe/H] ≲ −2.2 in both MCs, implying a low star formation efficiency of ∼0.01 Gyr⁻¹. The MC knees are more metal-poor than those of less massive MW dwarf galaxies such as Fornax, Sculptor, or Sagittarius. One possible interpretation is that the MCs formed in a lower-density environment than the MW, a hypothesis that is consistent with the paradigm that the MCs fell into the MW's gravitational potential only recently.

We report new simultaneous X-ray and radio continuum observations of 3FGL J0427.9−6704, a candidate member of the enigmatic class of transitional millisecond pulsars. These XMM-Newton and Australia Telescope Compact Array observations of this nearly edge-on, eclipsing low-mass X-ray binary were taken in the sub-luminous disk state at an X-ray luminosity of $\sim {10}^{33}{(d/2.3\mathrm{kpc})}^{2}\,$ erg s⁻¹. Unlike the few well-studied transitional millisecond pulsars, which spend most of their disk state in a characteristic high or low accretion mode with occasional flares, 3FGL J0427.9−6704 stayed in the flare mode for the entire X-ray observation of ∼20 hr, with the brightest flares reaching ∼2 × 10³⁴ erg s⁻¹. The source continuously exhibited flaring activity on timescales of ∼10–100 s in both the X-ray and optical/ultraviolet (UV). No measurable time delay between the X-ray and optical/UV flares is observed, but the optical/UV flares last longer, and the relative amplitudes of the X-ray and optical/UV flares show a large scatter. The X-ray spectrum can be well-fit with a partially absorbed power law (Γ ∼ 1.4–1.5), perhaps due to the edge-on viewing angle. Modestly variable radio continuum emission is present at all epochs, and is not eclipsed by the secondary, consistent with the presence of a steady radio outflow or jet. The simultaneous radio/X-ray luminosity ratio of 3FGL J0427.9−6704 is higher than any known transitional millisecond pulsars and comparable to that of stellar-mass black holes of the same X-ray luminosity, providing additional evidence that some neutron stars can be as radio-loud as black holes.

A broad and widely used class of stationary, linear, additive time-series models can have statistical properties that many authors have asserted imply that the underlying process must be nonlinear, nonstationary, multiplicative, or inconsistent with shot noise. This result is demonstrated with exact and numerical evaluation of the model flux distribution function and dependence of flux standard deviation on mean flux (here and in the literature called the rms–flux relation). These models can (1) exhibit normal, lognormal, or other flux distributions; (2) show linear or slightly nonlinear rms–mean flux dependencies; and (3) match arbitrary second-order statistics of the time-series data. Accordingly, the above assertions cannot be made on the basis of statistical time-series analysis alone. Also discussed are ambiguities in the meaning of terms relevant to this study—linear, stationary, and multiplicative—and functions that can transform observed fluxes to a normal distribution as well as or better than the logarithm.

The formation of planetesimals is a challenging problem in planet formation theory. A prominent scenario for overcoming dust growth barriers is the gravitational collapse of locally over-dense regions, shown to robustly produce ∼100 km–sized objects. Still, the conditions under which planetesimal formation occurs remain unclear. For collapse to proceed, the self-gravity of an over-density must overcome stellar tidal disruption on large scales and turbulent diffusion on small scales. Here, we relate the scales of streaming and Kelvin–Helmholtz instability (KHI), which both regulate particle densities on the scales of gravitational collapse, directly to planetesimal formation. We support our analytic findings by performing 3D hydrodynamical simulations of streaming and KHI and planetesimal formation. We find that the vertical extent of the particle mid-plane layer and the radial width of streaming instability filaments are set by the same characteristic length scale, thus governing the strength of turbulent diffusion on the scales of planetesimal formation. We present and successfully test a collapse criterion, 0.1Q β ⁻¹Z⁻¹ ≲ 1, and show that even for solar metallicities, planetesimals can form in dead zones of sufficiently massive disks. For a given gas Toomre parameter Q, pressure gradient β, metallicity Z, and local particle enhancement , the collapse criterion also provides a range of unstable scales, instituting a promising path for studying initial planetesimal mass distributions. Streaming instability is not required for planetesimal collapse but, by increasing , can evolve a system to instability.

We carry out a comparison study on the bar structure in the Illustris-1 and TNG100 simulations. At z = 0, 8.9% of 1232 disk galaxies with stellar masses $\gt {10}^{10.5}{M}_{\odot }$ in Illustris-1 are barred, while the numbers are 55% of 1269 in TNG100. The bar fraction as a function of stellar mass in TNG100 agrees well with the survey ${S}^{4}G$. The median redshifts of bar formation are ∼0.4–0.5 and ∼0.25 in TNG100 and Illustris-1, respectively. Bar fraction generally increases with stellar mass and decreases with gas fraction in both simulations. For galaxies with bars at z = 0, their bar formation time is generally anti-correlated with their gas fraction at high redshift. When the bars were formed, the disk gas fractions were mostly lower than 0.4. The much higher bar fraction in TNG100 probably benefits from the much lower gas fractions in massive disk galaxies since z ∼ 3, which may result from the combination of more effective stellar and AGN feedback. The latter may be the primary factor at z < 2. Meanwhile, in both simulations, barred galaxies have higher star formation rates before bar formation and have stronger AGN feedback, at all times, than unbarred galaxies. The properties of dark matter halos hosting massive disk galaxies are similar between the two simulations and should have a minor effect on the frequencies of different bars. For individual galaxies under similar halo environments across the two simulations, different baryonic physics can lead to striking discrepancies in morphology. The morphologies of individual galaxies are subject to the combined effects of environment and internal baryonic physics and are often not predictable.

We compare the microlensing-based continuum emission region size measurements in a sample of 15 gravitationally lensed quasars with estimates of luminosity-based thin disk sizes to constrain the temperature profile of the quasar continuum accretion region. If we adopt the standard thin disk model, we find a significant discrepancy between sizes estimated using the luminosity and those measured by microlensing of log(r_L/r_μ) = −0.57 ± 0.08 dex. If quasar continuum sources are simple, optically thick accretion disks with a generalized temperature profile $T(r)\propto {r}^{-\beta }$, the discrepancy between the microlensing measurements and the luminosity-based size estimates can be resolved by a temperature profile slope 0.37 < β < 0.56 at 1σ confidence. This is shallower than the standard thin disk model (β = 0.75) at 3σ significance. We consider alternate accretion disk models that could produce such a temperature profile and reproduce the empirical continuum size scaling with black hole mass, including disk winds or disks with nonblackbody atmospheres.

The reverse shock (RS) model is generally introduced to interpret the optical afterglows with the rapid rising and decaying, such as the early optical afterglow of GRB 990123 (which is also called the optical flash). In this paper, we collected 11 gamma-ray burst (GRB) early optical afterglows, which have signatures of dominant RS emission. Since the temporal slopes of the optical flashes are determined by both the medium density distribution index k and the electron spectral index p, we apply the RS model of the thin shell case to the optical flashes and determine the ambient medium of the progenitors. We find that the k value is in the range of 0–1.5. The k value in this paper is consistent with the result in Yi et al., where the forward shock model was applied to some onset bumps. However, the method adopted in this paper is only applicable to GRB afterglows with significant sharp rising and decaying RS emission. Our results indicate that the RS model can also be applied to confirm the circumburst medium, further implying that GRBs may have diverse circumburst media.

Black holes across a broad range of masses play a key role in the evolution of galaxies. The initial seeds of black holes formed at z ∼ 30 and grew over cosmic time by gas accretion and mergers. Using observational data for quasars and theoretical models for the hierarchical assembly of dark matter halos, we study the relative importance of gas accretion and mergers for black hole growth, as a function of redshift (0 < z < 10) and black hole mass (${10}^{3}\,{M}_{\odot }\lt {M}_{\bullet }\lt {10}^{10}\,{M}_{\odot }$). We find that (i) growth by accretion is dominant in a large fraction of the parameter space, especially at ${M}_{\bullet }\gt {10}^{8}\,{M}_{\odot }$ and z > 6; and (ii) growth by mergers is dominant at ${M}_{\bullet }\lt {10}^{5}\,{M}_{\odot }$ and z > 5.5, and at ${M}_{\bullet }\gt {10}^{8}\,{M}_{\odot }$ and z < 2. As the growth channel has direct implications for the black hole spin (with gas accretion leading to higher spin values), we test our model against ∼20 robust spin measurements available thus far. As expected, the spin tends to decline toward the merger-dominated regime, thereby supporting our model. The next generation of X-ray and gravitational-wave observatories (e.g., Lynx, AXIS, Athena, and LISA) will map out populations of black holes up to very high redshift (z ∼ 20), covering the parameter space investigated here in almost its entirety. Their data will be instrumental to providing a clear picture of how black holes grew across cosmic time.

We present a wide-field optical imaging search for electromagnetic counterparts to the likely neutron star–black hole (NS–BH) merger GW190814/S190814bv. This compact binary merger was detected through gravitational waves by the LIGO/Virgo interferometers, with masses suggestive of an NS–BH merger. We imaged the LIGO/Virgo localization region using the MegaCam instrument on the Canada–France–Hawaii Telescope (CFHT). We describe our hybrid observing strategy of both tiling and galaxy-targeted observations, as well as our image differencing and transient detection pipeline. Our observing campaign produced some of the deepest multiband images of the region between 1.7 and 8.7 days post-merger, reaching a 5σ depth of g > 22.8 (AB mag) at 1.7 days and i > 23.1 and i > 23.9 at 3.7 and 8.7 days, respectively. These observations cover a mean total integrated probability of 67.0% of the localization region. We find no compelling candidate transient counterparts to this merger in our images, which suggests that the lighter object was tidally disrupted inside of the BH's innermost stable circular orbit, the transient lies outside of the observed sky footprint, or the lighter object is a low-mass BH. We use 5σ source detection upper limits from our images in the NS–BH interpretation of this merger to constrain the mass of the kilonova ejecta to be M_ej ≲ 0. 015M_⊙ for a "blue" ($\kappa =0.5\,{\mathrm{cm}}^{2}\ {{\rm{g}}}^{-1}$) kilonova and M_ej ≲ 0. 04M_⊙ for a "red" ($\kappa =5\mbox{--}10\,{\mathrm{cm}}^{2}\ {{\rm{g}}}^{-1}$) kilonova. Our observations emphasize the key role of large-aperture telescopes and wide-field imagers such as CFHT MegaCam in enabling deep searches for electromagnetic counterparts to gravitational-wave events.

Interstellar carbonaceous dust is mainly formed in the innermost regions of circumstellar envelopes around carbon-rich asymptotic giant branch stars (AGBs). In these highly chemically stratified regions, atomic and diatomic carbon, along with acetylene, are the most abundant species after H₂ and CO. In a previous study, we addressed the chemistry of carbon (C and C₂) with H₂ showing that acetylene and aliphatic species form efficiently in the dust formation region of carbon-rich AGBs whereas aromatics do not. Still, acetylene is known to be a key ingredient in the formation of linear polyacetylenic chains, benzene, and polycyclic aromatic hydrocarbons (PAHs), as shown by previous experiments. However, these experiments have not considered the chemistry of carbon (C and C₂) with C₂H₂. In this work, by employing a sufficient amount of acetylene, we investigate its gas-phase interaction with atomic and diatomic carbon. We show that the chemistry involved produces linear polyacetylenic chains, benzene, and other PAHs, which are observed with high abundances in the early evolutionary phase of planetary nebulae. More importantly, we have found a nonnegligible amount of pure and hydrogenated carbon clusters as well as aromatics with aliphatic substitutions, both being a direct consequence of the addition of atomic carbon. The incorporation of alkyl substituents into aromatics can be rationalized by a mechanism involving hydrogen abstraction followed by methyl addition. All the species detected in the gas phase are incorporated into nanometric-sized dust analogs, which consist of a complex mixture of sp, sp², and sp³ hydrocarbons with amorphous morphology.

The discovery of a persistent radio source coincident with the first repeating fast radio burst, FRB 121102, and offset from the center of its dwarf host galaxy has been used as evidence for a link with young millisecond magnetars born in superluminous supernovae or long-duration gamma-ray bursts (LGRBs). A prediction of this scenario is that compact radio sources offset from the centers of dwarf galaxies may serve as signposts for at least some FRBs. Recently, Reines et al. presented the discovery of 20 such radio sources in nearby (z ≲ 0.055) dwarf galaxies, and argued that these cannot be explained by emission from H ii regions, normal supernova remnants, or normal radio supernovae. Instead, they attribute the emission to accreting wandering massive black holes. Here, we explore the alternative possibility that these sources are analogs of FRB 121102. We compare their properties—radio luminosities, spectral energy distributions, light curves, ratios of radio-to-optical flux, and spatial offsets—to FRB 121102, a few other well-localized FRBs, and potentially related systems, and find that these are all consistent as arising from the same population. We further compare their properties to the magnetar nebula model used to explain FRB 121102, as well as to theoretical off-axis LGRB light curves, and find overall consistency. Finally, we find a consistent occurrence rate relative to repeating FRBs and LGRBs. We outline key follow-up observations to further test these possible connections.

The detection of rapidly variable gamma-ray emission in active galactic nuclei has generated renewed interest in magnetospheric particle acceleration and emission scenarios. In order to explore its potential, we study the possibility of steady gap acceleration around the null surface of a rotating black hole magnetosphere. We employ a simplified (1D) description along with the general relativistic expression of Gauss's law, and we assume that the gap is embedded in the radiation field of a radiatively inefficient accretion flow. The model is used to derive expressions for the radial distribution of the parallel electric field component, the electron and positron charge density, the particle Lorentz factor, and the number density of γ-ray photons. We integrate the set of equations numerically, imposing suitable boundary conditions. The results show that the existence of a steady gap solution for a relative high value of the global current is in principle possible if charge injection of both species is allowed at the boundaries. We present gap solutions for different choices of the global current and the accretion rate. When put in context, our results suggest that the variable very-high-energy γ-ray emission in M87 could be compatible with a magnetospheric origin.

It is believed that massive galaxies have quenched their star formation because of active galactic nucleus feedback. However, recent studies have shown that some massive galaxies are still forming stars. We analyze the morphology of star formation regions for galaxies of stellar masses larger than 10^11.3M_⊙ at around redshift z_r = 0.5 using u − z color images. We find that about 20% of the massive galaxies are star-forming (SF) galaxies, and most of them (∼85%) have asymmetric structures induced by recent mergers. Moreover, for these asymmetric galaxies, we find that the asymmetry of the SF regions becomes larger for bluer galaxies. Using the Illustris simulation, we can qualitatively reproduce the observed relation between asymmetry parameter and color. Furthermore, using the merger trees in the simulation, we find a correlation between the color of the main branch galaxies at z_r = 0.5 and the sum of the star formation rates of the recently accreted galaxies, which implies that star formation of the accreted galaxies has contributed to the observed star formation of the massive (host) galaxies (ex situ star formation). Furthermore, we find two blue and symmetric galaxies, candidates for massive blue disks, in our observed sample, which indicates that about ∼10% of massive SF galaxies are forming stars in the normal mode of disk star formation (in situ star formation). With the simulation, we find that the disk galaxies at z_r ≈ 0.5 should have experienced few major mergers during the last 4.3 Gyr.

We present Atacama Large Millimeter/submillimeter Array maps of the starless molecular cloud core Ophiuchus/H-MM1 in the lines of deuterated ammonia (ortho-${\mathrm{NH}}_{2}{\rm{D}}$), methanol (${\mathrm{CH}}_{3}\mathrm{OH}$), and sulfur monoxide (SO). The dense core is seen in ${\mathrm{NH}}_{2}{\rm{D}}$ emission, whereas the ${\mathrm{CH}}_{3}\mathrm{OH}$ and SO distributions form a halo surrounding the core. Because methanol is formed on grain surfaces, its emission highlights regions where desorption from grains is particularly efficient. Methanol and sulfur monoxide are most abundant in a narrow zone that follows the eastern side of the core. This side is sheltered from the stronger external radiation field coming from the west. We show that photodissociation on the illuminated side can give rise to an asymmetric methanol distribution but that the stark contrast observed in H-MM1 is hard to explain without assuming enhanced desorption on the shaded side. The region of the brightest emission has a wavy structure that rolls up at one end. This is the signature of Kelvin–Helmholtz instability occurring in sheared flows. We suggest that in this zone, methanol and sulfur are released as a result of grain–grain collisions induced by shear vorticity.

We study black hole–host galaxy correlations, and the relation between the overmassiveness (the distance from the average M_BH–σ relation) of supermassive black holes (SMBHs) and the star formation histories of their host galaxies in the Illustris and TNG100 simulations. We find that both simulations are able to produce black hole scaling relations in general agreement with observations at z = 0, but with noticeable discrepancies. Both simulations show an offset from the observations for the M_BH–σ relation, and the relation between M_BH and the Sérsic index. The relation between M_BH and stellar mass M_* is tighter than the observations, especially for TNG100. For massive galaxies in both simulations, the hosts of overmassive SMBHs (those above the mean M_BH–σ relation) tend to have larger Sérsic indices and lower baryon conversion efficiency, suggesting a multidimensional link between SMBHs and the properties of their hosts. In Illustris, the hosts of overmassive SMBHs have formed earlier and have lower present-day star formation rates, in qualitative agreement with the observations for massive galaxies with σ > 100 km s⁻¹. For low-mass galaxies, such a correlation still holds in Illustris but does not exist in the observed data. For TNG100, the correlation between SMBH overmassiveness and star formation history is much weaker. The hosts of overmassive SMBHs generally have consistently larger star formation rates throughout history. These galaxies have higher stellar mass as well, due to the strong M_BH–M_* correlation. Our findings show that simulated SMBH scaling relations and correlations are sensitive to features in the modeling of SMBHs.

Now over seven years into its journey beyond the heliopause, Voyager 1 continues to return unprecedented observations of energetic particles, magnetic fields, and plasma emissions from the very local interstellar medium. Shortly after its heliopause crossing, Voyager 1 discovered an unusual time-varying galactic cosmic-ray anisotropy, characterized by smoothly changing intensity reductions in particles propagating nearly perpendicular to the magnetic field; outside of this isolated region, cosmic rays appear mostly unvarying, without a significant radial gradient. These small (∼15%) but lasting (∼100 to ∼630 days) anisotropic events are still not fully understood. Nevertheless, they serve as clear markers, together with shorter-lived cosmic-ray intensity enhancements, electron plasma oscillations, and weak laminar shocks, that even beyond the heliopause, the Sun's variable output significantly influences its surroundings. So far, these unusual energetic particle occurrences have mainly been studied using integrated proton intensities of ∼20 MeV and higher. Using data from the Voyager 1 Cosmic Ray Subsystem, we extend the analysis to electrons, as well as lower energy protons, and discover the surprising new result that the ∼3 to ∼105 MeV electrons remain mostly isotropic and unchanging, in sharp contrast to their proton counterparts. We search for clues to explain this underlying species dependence and rule out potential causes related to instrumental effects, velocity and energy, trapping and energy loss, drifts, and turbulence-induced scattering. We also explore some plausible mechanisms and open the door for more detailed follow-up theories and simulations.

We analyze an extremely deep 450 μm image (1σ = 0.56 mJy beam⁻¹) of a ≃300 arcmin² area in the CANDELS/COSMOS field as part of the Sub-millimeter Common User Bolometric Array-2 Ultra Deep Imaging EAO Survey. We select a robust (signal-to-noise ratio ≥4) and flux-limited (≥4 mJy) sample of 164 submillimeter galaxies (SMGs) at 450 μm that have K-band counterparts in the COSMOS2015 catalog identified from radio or mid-infrared imaging. Utilizing this SMG sample and the 4705 K-band-selected non-SMGs that reside within the noise level ≤1 mJy beam⁻¹ region of the 450 μm image as a training set, we develop a machine-learning classifier using K-band magnitude and color–color pairs based on the 13-band photometry available in this field. We apply the trained machine-learning classifier to the wider COSMOS field (1.6 deg²) using the same COSMOS2015 catalog and identify a sample of 6182 SMG candidates with similar colors. The number density, radio and/or mid-infrared detection rates, redshift and stellar-mass distributions, and the stacked 450 μm fluxes of these SMG candidates, from the S2COSMOS observations of the wide field, agree with the measurements made in the much smaller CANDELS field, supporting the effectiveness of the classifier. Using this SMG candidate sample, we measure the two-point autocorrelation functions from z = 3 down to z = 0.5. We find that the SMG candidates reside in halos with masses of ≃(2.0 ± 0.5) × 10¹³h⁻¹M_☉ across this redshift range. We do not find evidence of downsizing that has been suggested by other recent observational studies.

Nonlinear force-free field (NLFFF) modeling has been extensively used as a tool to infer three-dimensional (3D) magnetic field structure. In this study, the dependency of the NLFFF calculation with respect to the initial guess of the 3D magnetic field is investigated. While major parts of the previous studies used the potential field as the initial guess in NLFFF modeling, we adopt linear force-free fields with different constant force-free alpha as the initial guesses. This method enables us to investigate the uniqueness of the magnetic field obtained by the NLFFF extrapolation with respect to the initial guess. The dependence of the initial conditions on NLFFF extrapolation is smaller in the strong magnetic field region. Therefore, the magnetic field at lower heights (<10 Mm) tends to be less affected by the initial conditions (correlation coefficient C > 0.9 with different initial conditions); although, the Lorentz force is concentrated at lower heights.

Exploiting the data from the GAs Stripping Phenomena in galaxies with MUSE (GASP) survey, we study the gas-phase metallicity scaling relations of a sample of 29 cluster galaxies undergoing ram pressure stripping and of a reference sample of (16 cluster and 16 field) galaxies with no significant signs of gas disturbance. We adopt the pyqz code to infer the mean gas metallicity at the effective radius and achieve a well-defined mass–metallicity relation (MZR) in the stellar mass range ${10}^{9.25}\leqslant {M}_{\star }\leqslant {10}^{11.5}\,{M}_{\odot }$ with a scatter of 0.12 dex. At any given mass, reference cluster and stripping galaxies have similar metallicities, while the field galaxies with M_⋆ < 10^10.25M_⊙ show on average lower gas metallicity than galaxies in clusters. Our results indicate that at the effective radius, the chemical properties of the stripping galaxies are independent of the ram pressure stripping mechanism. Nonetheless, at the lowest masses, we detect four stripping galaxies well above the common MZR that suggest a more complex scenario. Overall, we find signs of an anticorrelation between the metallicity and both the star formation rate and the galaxy size, in agreement with previous studies. No significant trends are instead found with the halo mass, clustercentric distance, and local galaxy density in clusters. In conclusion, we advise a more detailed analysis of the spatially resolved gas metallicity maps of the galaxies, able to highlight effects of gas redistribution inside the disk due to ram pressure stripping.

Collisionless shocks are often studied in two spatial dimensions (2D) to gain insights into the 3D case. We analyze diffusive shock acceleration for an arbitrary number $N\in {\mathbb{N}}$ of dimensions. For a nonrelativistic shock of compression ratio ${ \mathcal R }$, the spectral index of the accelerated particles is ${s}_{{\rm{E}}}=1+N/({ \mathcal R }-1);$ this curiously yields, for any N, the familiar ${s}_{{\rm{E}}}=2$ (i.e., equal energy per logarithmic particle energy bin) for a strong shock in a monatomic gas. A precise relation between ${s}_{{\rm{E}}}$ and the anisotropy along an arbitrary relativistic shock is derived and is used to obtain an analytic expression for ${s}_{{\rm{E}}}$ in the case of isotropic angular diffusion, affirming an analogous result in 3D. In particular, this approach yields ${s}_{{\rm{E}}}=(1+\sqrt{13})/2\simeq 2.30$ in the ultrarelativistic shock limit for N = 2, and ${s}_{{\rm{E}}}(N\to \infty )=2$ for any strong shock. The angular eigenfunctions of the isotropic-diffusion transport equation reduce in 2D to elliptic cosine functions, providing a rigorous solution to the problem; the first function upstream already yields a remarkably accurate approximation. We show how these and additional results can be used to promote the study of shocks in 3D.

The detections of GW170817 and GRB 170817A revealed that at least some short gamma-ray bursts (sGRB) are associated with the merger of neutron-star compact binaries. The gamma-rays are thought to result from the formation of collimated jets, but the details of this process continue to elude us. One important feature of gamma-ray bursts is the emission profile of the jet as a function of viewing angle. We present two related methods to measure the effective angular width, ${\theta }_{B}$, of sGRB jets using gravitational-wave (GW) and gamma-ray data, assuming all sGRBs have the same angular dependence for their luminosities. The first is a counting experiment that requires minimal knowledge about each event, beyond whether or not they were detected in gamma-rays. The second method uses GW and electromagnetic data to estimate parameters of the source. We additionally outline a model-independent method to infer the full jet structure of sGRBs using a nonparametric approach. Applying our methods to GW170817 and GW190425, we find weak constraints on the sGRB luminosity profile. We project that with 5 and 100 binary neutron star detections, the counting method would constrain the relative uncertainty in ${\theta }_{B}$ to within $51 \%$ and $12 \%$, respectively. Incorporating GW parameter estimation provides only marginal improvements. We conclude that the majority of the information about jet structure comes from the relative sensitivities of GW and gamma-ray detectors as encoded in simple counting experiments.

Turbulence is a crucial factor in many models of planet formation, but it has only been directly constrained among a small number of planet-forming disks. Building on the upper limits on turbulence placed in disks around HD 163296 and TW Hya, we present ALMA CO J = 2–1 line observations at ∼03 (20–50 au) resolution and 80 ms⁻¹ channel spacing of the disks around DM Tau, MWC 480, and V4046 Sgr. Using parametric models of disk structure, we robustly detect nonthermal gas motions around DM Tau of between 0.25c_s and 0.33c_s, with the range dominated by systematic effects, making this one of the only systems with directly measured nonzero turbulence. Using the same methodology, we place stringent upper limits on the nonthermal gas motion around MWC 480 (<0.08c_s) and V4046 Sgr (<0.12c_s). The preponderance of upper limits in this small sample and the modest turbulence levels consistent with dust studies suggest that weak turbulence (α ≲ 10⁻³) may be a common, albeit not universal, feature of planet-forming disks. We explore the particular physical conditions around DM Tau that could lead this system to be more turbulent than the others.

We quantitatively investigate the contribution of large dust particles to the polarimetric response in comets using the light-scattering properties of model agglomerated debris particles. We demonstrate that large, supermicron-sized particles have a decreasing role on the degree of linear polarization at phase angle α ≤ 80°, and the effect of particles greater than 10 μm is minimal. At larger phase angles, they may only slightly increase the measured percent of polarization by up to 1%. Omitting the effects of these particles in modeling the observations only slightly affects the retrievals of the microphysical properties of dust in comets and could lead to a small underestimation of the index in a power-law size distribution and population of weakly absorbing dust particles.

Assuming a gravitational origin for the Fe iiiλλ2039-2113 redshift and using microlensing based estimates of the size of the region emitting this feature, we obtain individual measurements of the virial factor, f, in 10 quasars. The average values for the Balmer lines, $\langle {f}_{{\rm{H}}\beta }\rangle =0.43\pm 0.20$ and $\langle {f}_{{\rm{H}}\alpha }\rangle =0.50\pm 0.24$, are in good agreement with the results of previous studies for objects with lines of comparable widths. In the case of Mg ii, consistent results, ${f}_{\mathrm{Mg}{\rm{II}}}\sim 0.44$, can be also obtained accepting a reasonable scaling for the size of the emitting region. The modeling of the cumulative histograms of individual measurements, CDF(f), indicates a relatively high value for the ratio between isotropic and cylindrical motions, $a\sim 0.4\mbox{--}0.7$. On the contrary, we find very large values of the virial factor associated to the Fe iiiλλ2039-2113 blend, ${f}_{\mathrm{Fe}{\rm{III}}}=14.3\pm 2.4$, which can be explained if this feature arises from a flattened nearly face-on structure, similar to the accretion disk.

We examine morphology-separated color–mass diagrams to study the quenching of star formation in ∼100,000 (z ∼ 0) Sloan Digital Sky Survey (SDSS) and ∼20,000 (z ∼ 1) Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey (CANDELS) galaxies. To classify galaxies morphologically, we developed Galaxy Morphology Network (GaMorNet), a convolutional neural network that classifies galaxies according to their bulge-to-total light ratio. GaMorNet does not need a large training set of real data and can be applied to data sets with a range of signal-to-noise ratios and spatial resolutions. GaMorNet's source code as well as the trained models are made public as part of this work. We first trained GaMorNet on simulations of galaxies with a bulge and a disk component and then transfer learned using ∼25% of each data set to achieve misclassification rates of ≲5%. The misclassified sample of galaxies is dominated by small galaxies with low signal-to-noise ratios. Using the GaMorNet classifications, we find that bulge- and disk-dominated galaxies have distinct color–mass diagrams, in agreement with previous studies. For both SDSS and CANDELS galaxies, disk-dominated galaxies peak in the blue cloud, across a broad range of masses, consistent with the slow exhaustion of star-forming gas with no rapid quenching. A small population of red disks is found at high mass (∼14% of disks at z ∼ 0 and 2% of disks at z ∼ 1). In contrast, bulge-dominated galaxies are mostly red, with much smaller numbers down toward the blue cloud, suggesting rapid quenching and fast evolution across the green valley. This inferred difference in quenching mechanism is in agreement with previous studies that used other morphology classification techniques on much smaller samples at z ∼ 0 and z ∼ 1.

We provide a new fitting formula of the matter bispectrum in the nonlinear regime calibrated by high-resolution cosmological N-body simulations of 41 cold dark matter (wCDM, w =  constant) models around the Planck 2015 best-fit parameters. As the parameterization in our fitting function is similar to that in Halofit, our fitting is named BiHalofit. The simulation volume is sufficiently large ($\gt 10\,{\mathrm{Gpc}}^{3}$) to cover almost all measurable triangle bispectrum configurations in the universe. The function is also calibrated using one-loop perturbation theory at large scales ($k\lt 0.3\,h\,{\mathrm{Mpc}}^{-1}$). Our formula reproduced the matter bispectrum to within 10% (15%) accuracy in the Planck 2015 model at wavenumber $k\lt 3\,(10)\,h\,{\mathrm{Mpc}}^{-1}$ and redshifts z = 0–3. The other 40 wCDM models obtained poorer fits, with accuracy approximating 20% at $k\lt 3\,h\,{\mathrm{Mpc}}^{-1}$ and $z=0\mbox{--}1.5$ (the deviation includes the 10%-level sample variance of the simulations). We also provide a fitting formula that corrects the baryonic effects such as radiative cooling and active galactic nucleus feedback, using the latest hydrodynamical simulation IllustrisTNG. We demonstrate that our new formula more accurately predicts the weak-lensing bispectrum than the existing fitting formulae. This formula will assist current and future weak-lensing surveys and cosmic microwave background lensing experiments. Numerical codes of the formula are available, written in Python (https://toshiyan.github.io/clpdoc/html/basic/basic.html#module-basic.bispec), C, and Fortran (http://cosmo.phys.hirosaki-u.ac.jp/takahasi/codes_e.htm).

We investigate whether the correlation between the hard X-ray photon index (${\rm{\Gamma }}$) and accretion rate for super-Eddington accreting quasars is different from that for sub-Eddington accreting quasars. We construct a sample of 113 bright quasars from the Sloan Digital Sky Survey Data Release 14 quasar catalog, with 38 quasars as the super-Eddington subsample and 75 quasars as the sub-Eddington subsample. We derive black hole masses using a simple-epoch virial mass formula based on the ${\rm{H}}\beta$ lines, and we use the standard thin disk model to derive the dimensionless accretion rates ($\dot{{\mathscr{M}}}$) for our sample. The X-ray data for these quasars are collected from the Chandra and XMM-Newton archives. We fit the hard X-ray spectra using a single power-law model to obtain ${\rm{\Gamma }}$ values. We find a statistically significant (${R}_{{\rm{S}}}=0.43$, $p=7.75\times {10}^{-3}$) correlation between ${\rm{\Gamma }}$ and $\dot{{\mathscr{M}}}$ for the super-Eddington subsample. The ${\rm{\Gamma }}$–$\dot{{\mathscr{M}}}$ correlation for the sub-Eddington subsample is also significant, but weaker (${R}_{{\rm{S}}}=0.30$, $p=9.98\times {10}^{-3}$). Linear regression analysis shows that ${\rm{\Gamma }}=(0.34\pm 0.11)\mathrm{log}\dot{{\mathscr{M}}}+(1.71\pm 0.17)$ and ${\rm{\Gamma }}=(0.09\pm 0.04)\mathrm{log}\dot{{\mathscr{M}}}+(1.93\pm 0.04)$ for the super- and sub-Eddington subsamples, respectively. The ${\rm{\Gamma }}$–$\dot{{\mathscr{M}}}$ correlations of the two subsamples are different, suggesting different disk–corona connections in these two types of systems. We propose one qualitative explanation of the steeper ${\rm{\Gamma }}$–$\dot{{\mathscr{M}}}$ correlation in the super-Eddington regime that involves larger seed photon fluxes received by the compact coronae from the thick disks in super-Eddington accreting quasars.

Merging is potentially the dominant process in galaxy formation, yet there is still debate about its history over cosmic time. To address this, we classify major mergers and measure galaxy merger rates up to z ∼ 3 in all five CANDELS fields (UDS, EGS, GOODS-S, GOODS-N, COSMOS) using deep learning convolutional neural networks trained with simulated galaxies from the IllustrisTNG cosmological simulation. The deep learning architecture used is objectively selected by a Bayesian optimization process over the range of possible hyperparameters. We show that our model can achieve 90% accuracy when classifying mergers from the simulation and has the additional feature of separating mergers before the infall of stellar masses from post-mergers. We compare our machine-learning classifications on CANDELS galaxies and compare with visual merger classifications from Kartaltepe et al., and show that they are broadly consistent. We finish by demonstrating that our model is capable of measuring galaxy merger rates, ${ \mathcal R }$, that are consistent with results found for CANDELS galaxies using close pairs statistics, with ${ \mathcal R }{(z)=0.02\pm 0.004\times (1+z)}^{2.76\pm 0.21}$. This is the first general agreement between major mergers measured using pairs and structure at z < 3.

We measure the ionizing photon production efficiency (ξ_ion) of low-mass galaxies (10^7.8–10^9.8M_⊙) at 1.4 < z < 2.7 to better understand the contribution of dwarf galaxies to the ionizing background and reionization. We target galaxies that are magnified by strong-lensing galaxy clusters and use Keck/MOSFIRE to measure nebular emission-line fluxes and Hubble Space Telescope to measure the rest-UV and rest-optical photometry. We present two methods of stacking. First, we take the average of the log of Hα-to-UV luminosity ratios (L_Hα/L_UV) of galaxies to determine the standard log(ξ_ion). Second, we take the logarithm of the total L_Hα over the total L_UV. We prefer the latter, as it provides the total ionizing UV luminosity density of galaxies when multiplied by the nonionizing UV luminosity density. log(ξ_ion) calculated from the second method is ∼0.2 dex higher than the first method. We do not find any strong dependence between log(ξ_ion) and stellar mass, far-UV magnitude (M_UV), or UV spectral slope (β). We report a value of log(ξ_ion) ∼ 25.47 ± 0.09 for our UV-complete sample ($-22\lt {M}_{\mathrm{UV}}\lt -17.3$) and ∼25.37 ± 0.11 for our mass-complete sample (7.8 < log(M_*) < 9.8). These values are consistent with measurements of more massive, more luminous galaxies in other high-redshift studies that use the same stacking technique. Our log(ξ_ion) is 0.2–0.3 dex higher than low-redshift galaxies of similar mass, indicating an evolution in the stellar properties, possibly due to metallicity or age. We also find a correlation between log(ξ_ion) and the equivalent widths of Hα and [O iii] λ5007 fluxes, confirming that these equivalent widths can be used to estimate ξ_ion.

As helioseismology matures and turns into a precision science, modeling finite-frequency, geometric, and systematical effects is becoming increasingly important. Here we introduce a general formulation for treating perturbations of arbitrary tensor rank in spherical geometry using fundamental ideas of quantum mechanics and their extensions in geophysics. We include line-of-sight projections and center-to-limb differences in line formation heights in our analysis. We demonstrate the technique by computing a travel-time sensitivity kernel for sound-speed perturbations. The analysis produces the spherical harmonic coefficients of the sensitivity kernels, which leads to better-posed and computationally efficient inverse problems.

We present photometric and spectroscopic observations of SN 2013aa and SN 2017cbv, two nearly identical type Ia supernovae (SNe Ia) in the host galaxy NGC 5643. The optical photometry has been obtained using the same telescope and instruments used by the Carnegie Supernova Project. This eliminates most instrumental systematics and provides light curves in a stable and well-understood photometric system. Having the same host galaxy also eliminates systematics due to distance and peculiar velocity, providing an opportunity to directly test the relative precision of SNe Ia as standard candles. The two SNe have nearly identical decline rates, negligible reddenings, and remarkably similar spectra, and, at a distance of ∼20 Mpc, they are ideal potential calibrators for the absolute distance using primary indicators such as Cepheid variables. We discuss to what extent these two SNe can be considered twins and compare them with other supernova "siblings" in the literature and their likely progenitor scenarios. Using 12 galaxies that hosted two or more SNe Ia, we find that when using SNe Ia, and after accounting for all sources of observational error, one gets consistency in distance to 3%.

We mapped two molecular cloud cores in the Orion A cloud with the 7 m Array of the Atacama Compact Array (ACA) of the Atacama Large Millimeter/submillimeterArray (ALMA) and with the Nobeyama 45 m radio telescope. These cores have bright N₂D⁺ emission in single-pointing observations with the Nobeyama 45 m radio telescope, have a relatively high deuterium fraction, and are thought to be close to the onset of star formation. One is a star-forming core, and the other is starless. These cores are located along filaments observed in N₂H⁺ and show narrow line widths of 0.41 km s⁻¹ and 0.45 km s⁻¹ in N₂D⁺, respectively, with the Nobeyama 45 m telescope. Both cores were detected with the ALMA ACA 7 m Array in the continuum and molecular lines at Band 6. The starless core G211 shows a clumpy structure with several sub-cores, which in turn show chemical differences. Also, the sub-cores in G211 have internal motions that are almost purely thermal. The starless sub-core G211D, in particular, shows a hint of the inverse P Cygni profile, suggesting infall motion. The star-forming core G210 shows an interesting spatial feature of two N₂D⁺ peaks of similar intensity and radial velocity located symmetrically with respect to the single dust continuum peak. One interpretation is that the two N₂D⁺ peaks represent an edge-on pseudo-disk. The CO outflow lobes, however, are not directed perpendicular to the line connecting both N₂D⁺ peaks.

We used two XMM-Newton and six Neutron Star Interior Composition Explorer observations to investigate the fractional rms amplitude of the millihertz quasiperiodic oscillations (mHz QPOs) in the neutron-star low-mass X-ray binary 4U 1636–53. We studied, for the first time, the fractional rms amplitude of the mHz QPOs versus energy in 4U 1636–53 down to 0.2 keV. We find that, as the energy increases from ∼0.2 to ∼3 keV, the rms amplitude of the mHz QPOs increases, different from the decreasing trend that has been previously observed above 3 keV. This finding has not yet been predicted by any current theoretical model; however, it provides an important observational feature to speculate whether a newly discovered mHz oscillation originates from the marginally stable nuclear burning process on the neutron-star surface.

This is the second paper in a series where we examine the physics of pair producing gaps in low-luminosity accreting supermassive black hole systems. In this paper, we carry out time-dependent self-consistent fully general relativistic 1D particle-in-cell simulations of the gap, including full inverse Compton scattering and photon tracking. Similar to the previous paper, we find a highly time-dependent solution where a macroscopic vacuum gap can open quasiperiodically, producing bursts of ${e}^{\pm }$ pairs and high energy radiation. We present the light curve, particle spectrum, and photon spectrum from this process. Using an empirical scaling relation, we rescale the parameters to the inferred values at the base of the jet in M87, and find that the observed TeV flares could potentially be explained by this model under certain parameter assumptions.

Temporal analysis of blazar flux is a powerful tool to draw inferences about the emission processes and physics of these sources. In the most general case, the available light curves are irregularly sampled and influenced by gaps, and in addition are also affected by correlated noise, making their analysis complicated. Gaussian processes may offer a viable tool to assess the statistical significance of proposed periods in light curves characterized by any sampling and noise pattern. We infer the significance of the periods proposed in the literature for two well known blazars with multiple claims of possible year-long periodicity: PG 1553 + 113 and PKS 2155–304, in the high-energy and optical bands. Adding a periodic component to the modeling gives a better statistical description of the analyzed light curves. The improvement is rather solid for PG 1553 + 113, both at high energies and in the optical, while for PKS 2155–304 at high energies the improvement is not yet strong enough to allow cogent claims, and no evidence for periodicity emerged from the analysis in the optical. Modeling a light curve by means of Gaussian processes, in spite of being relatively computationally demanding, allows us to derive a wealth of information about the data under study and suggests an original analysis framework for light curves of astrophysical interest.

Measuring the global magnetic field of the solar corona remains exceptionally challenging. The fine-scale density structures observed in white-light images taken during total solar eclipses are currently the best proxies for inferring the magnetic field direction in the corona from the solar limb out to several solar radii (R_⊙). We present, for the first time, the topology of the coronal magnetic field continuously between 1 and 6 R_⊙, as quantitatively inferred with the rolling Hough transform for 14 unique eclipse coronae that span almost two complete solar cycles. We find that the direction of the coronal magnetic field does not become radial until at least 3 R_⊙, with a high variance between 1.5 and 3 R_⊙ at different latitudes and phases of the solar cycle. We find that the most nonradial coronal field topologies occur above regions with weaker magnetic field strengths in the photosphere, while stronger photospheric fields are associated with highly radial field lines in the corona. In addition, we find an abundance of field lines that extend continuously from the solar surface out to several solar radii at all latitudes, regardless of the presence of coronal holes. These results have implications for testing and constraining coronal magnetic field models, and for linking in situ solar wind measurements to their sources at the Sun.

A complete understanding of the formation process of close binaries relies on the reliable determination of their masses and ages, as well as the interior structure of pre-main-sequence (PMS) binaries. PMS eclipsing binaries containing stellar oscillations are therefore benchmarks since the binarity makes it possible to measure the masses and radii independently with great accuracy, while stellar oscillations represent a unique method of probing stellar interiors. Here we report the discovery of KIC 9850387, a short-period PMS eclipsing binary exhibiting hybrid γ Dor-δ Sct pulsations that is also the inner binary of a probable hierarchical triple system. From the light-curve and radial-velocity modeling we determine the masses and radii of the component stars, which suggest the probable PMS nature of the system. Based on four years of Kepler data, the intrinsic oscillations of the star are analyzed. The pulsation spectrum shows 17 low-frequency peaks spaced at exactly equidistant periods that are identified as dipole gravity modes. The practically constant period spacing indicates an extremely slow near-core rotation of the pulsator with a period deduced to be longer than 1 yr. This enables us to fit the pulsation frequencies precisely with non-rotating models. The stellar parameters yielded by asteroseismology modeling are in consistent with the dynamic ones given by the binary model. The results indicate that the pulsator is a young PMS star with an age between 6.4 and 7.1 Myr. KIC 9850387 is therefore the first PMS eclipsing binary identified by asteroseismology.

We use 13 seasons of R-band photometry from the 1.2 m Leonard Euler Swiss Telescope at La Silla to examine microlensing variability in the quadruply imaged lensed quasar WFI 2026–4536. The lightcurves exhibit ∼0.2 mag of uncorrelated variability across all epochs and a prominent single feature of ∼0.1 mag within a single season. We analyze this variability to constrain the size of the quasar's accretion disk. Adopting a nominal inclination of 60°, we find an accretion disk scale radius of $\mathrm{log}({r}_{s}/\mathrm{cm})={15.74}_{-0.29}^{+0.34}$ at a rest-frame wavelength of 2043 Å, and we estimate a black hole mass of $\mathrm{log}({M}_{\mathrm{BH}}/{M}_{\odot })={9.18}_{-0.34}^{+0.39}$, based on the C iv line in VLT spectra. This size measurement is fully consistent with the quasar accretion disk size—black hole mass relation, providing another system in which the accretion disk is larger than predicted by thin-disk theory.

We utilize ALMA archival data to estimate the dust disk size of 152 protoplanetary disks in Lupus (1–3 Myr), Chamaeleon I (2–3 Myr), and Upper-Sco (5–11 Myr). We combine our sample with 47 disks from Tau/Aur and Oph whose dust disk radii were estimated, as here, through fitting radial profile models to visibility data. We use these 199 homogeneously derived disk sizes to identify empirical disk–disk and disk–host property relations as well as to search for evolutionary trends. In agreement with previous studies, we find that dust disk sizes and millimeter luminosities are correlated, but show for the first time that the relationship is not universal between regions. We find that disks in the 2–3 Myr old Cha I are not smaller than disks in other regions of similar age, and confirm the Barenfeld et al. finding that the 5–10 Myr USco disks are smaller than disks belonging to younger regions. Finally, we find that the outer edge of the solar system, as defined by the Kuiper Belt, is consistent with a population of dust disk sizes which have not experienced significant truncation.

We present the results from a monitoring campaign made with the Neil Gehrels Swift Observatory of the M51 galaxies, which contain several variable ultraluminous X-ray sources (ULXs). The ongoing campaign started in 2018 May, and we report here on ∼1.5 yr of observations. The campaign, which consists of 106 observations, has a typical cadence of 3–6 days, and has the goal of determining the long-term X-ray variability of the ULXs. Two of the most variable sources were ULX7 and ULX8, both of which are known to be powered by neutron stars that are exceeding their isotropic Eddington luminosities by factors of up to 100. This is further evidence that neutron-star-powered ULXs are the most variable. Our two main results are, first, that ULX7 exhibits a periodic flux modulation with a period of 38 days varying over a magnitude and a half in flux from peak to trough. Since the orbital period of the system is known to be 2 days, the modulation is superorbital, which is a near-ubiquitous property of ULX pulsars. Second, we identify a new transient ULX, M51 XT-1, the onset of which occurred during our campaign, reaching a peak luminosity of ∼10⁴⁰ erg s⁻¹, before gradually fading over the next ∼200 days until it slipped below the detection limit of our observations. Combined with the high-quality Swift/X-ray Telescope lightcurve of the transient, serendipitous observations made with Chandra and XMM-Newton provide insights into the onset and evolution of a likely super-Eddington event.

While the Advanced LIGO and Virgo gravitational-wave (GW) experiments now regularly observe binary black hole (BBH) mergers, the evolutionary origin of these events remains a mystery. Analysis of the BBH spin distribution may shed light on this mystery, offering a means of discriminating between different binary formation channels. Using the data from Advanced LIGO and Virgo's first and second observing runs, here we seek to carefully characterize the distribution of effective spin ${\chi }_{\mathrm{eff}}$ among BBHs, hierarchically measuring the distribution's mean μ and variance σ² while accounting for selection effects and degeneracies between spin and other black hole parameters. We demonstrate that the known population of BBHs have spins that are both small, with μ ≈ 0, and very narrowly distributed, with σ² ≤ 0.07 at 95% credibility. We then explore what these ensemble properties imply about the spins of individual BBH mergers, reanalyzing existing GW events with a population-informed prior on their effective spin. Under this analysis, the BBH GW170729, which previously excluded ${\chi }_{\mathrm{eff}}=0$, is now consistent with zero effective spin at ∼10% credibility. More broadly, we find that uninformative spin priors generally yield overestimates for the effective spin magnitudes of compact binary mergers.

Traditionally, the strongest magnetic fields on the Sun have been measured in sunspot umbrae. More recently, however, much stronger fields have been measured at the ends of penumbral filaments carrying the Evershed and counter-Evershed flows. Superstrong fields have also been reported within a light bridge separating two umbrae of opposite polarities. We aim to accurately determine the strengths of the strongest fields in a light bridge using an advanced inversion technique and to investigate their detailed structure. We analyze observations from the spectropolarimeter on board the Hinode spacecraft of the active region AR 11967. The thermodynamic and magnetic configurations are obtained by inverting the Stokes profiles using an inversion scheme that allows multiple height nodes. Both the traditional 1D inversion technique and the so-called 2D coupled inversions, which take into account the point-spread function of the Hinode telescope, are used. We find a compact structure with an area of 32.7 arcsec² within a bipolar light bridge with field strengths exceeding 5 kG, confirming the strong fields in this light bridge reported in the literature. Two regions associated with downflows of ∼5 km s⁻¹ harbor field strengths larger than 6.5 kG, covering a total area of 2.97 arcsec². The maximum field strength found is 8.2 kG, which is the largest ever observed field in a bipolar light bridge up to now.

We build an evolution model of the central black hole that depends on the processes of gas accretion, the capture of stars, mergers, and electromagnetic torque. In the case of gas accretion in the presence of cooling sources, the flow is momentum driven, after which the black hole reaches a saturated mass; subsequently, it grows only by stellar capture and mergers. We model the evolution of the mass and spin with the initial seed mass and spin in ΛCDM cosmology. For stellar capture, we have assumed a power-law density profile for the stellar cusp in a framework of relativistic loss cone theory that includes the effects of black hole spin, Carter's constant, loss cone angular momentum, and capture radius. Based on this, the predicted capture rates of 10⁻⁵ to 10⁻⁶ yr⁻¹ are closer to the observed range. We have considered the merger activity to be effective for z ≲ 4, and we self-consistently include the Blandford–Znajek torque. We calculate these effects on the black hole growth individually and in combination, for deriving the evolution. Before saturation, accretion dominates the black hole growth (∼95% of the final mass), and subsequently stellar capture and mergers take over with roughly equal contributions. The simulations of the evolution of the M_•–σ relation using these effects are consistent with available observations. We run our model backward in time and retrodict the parameters at formation. Our model will provide useful inputs for building demographics of the black holes and in formation scenarios involving stellar capture.

NASA's WB-57 High Altitude Research Program provides a deployable, mobile, and stratospheric platform for scientific research. Airborne platforms are of particular value for making coronal observations during total solar eclipses because of their ability both to follow the Moon's shadow and to get above most of the atmospheric air mass that can interfere with astronomical observations. We used the 2017 August 21 eclipse as a pathfinding mission for high-altitude airborne solar astronomy, using the existing high-speed visible-light and near/midwave infrared imaging suite mounted in the WB-57 nose cone. In this paper, we describe the aircraft, the instrument, and the 2017 mission; operations and data acquisition; and preliminary analysis of data quality from the existing instrument suite. We describe benefits and technical limitations of this platform for solar and other astronomical observations. We present a preliminary analysis of the visible-light data quality and discuss the limiting factors that must be overcome with future instrumentation. We conclude with a discussion of lessons learned from this pathfinding mission and prospects for future research at upcoming eclipses, as well as an evaluation of the capabilities of the WB-57 platform for future solar astronomy and general astronomical observation.

We present the luminosity function (LF) for ultraluminous Lyα emitting galaxies (LAEs) at z = 6.6. We define ultraluminous LAEs (ULLAEs) as galaxies with $\mathrm{log}L(\mathrm{Ly}\alpha )\gt 43.5$ erg s⁻¹. We select our main sample using the g', r', i', z', and NB921 observations of a wide-area (30 deg²) Hyper Suprime-Cam survey of the north ecliptic pole (NEP) field. We select candidates with $g^{\prime} ,r^{\prime} ,i^{\prime} \gt 26$, NB921 ≤ 23.5, and $\mathrm{NB}921-z^{\prime} \leqslant 1.3$. Using the DEIMOS spectrograph on Keck II, we confirm 9 of our 14 candidates as ULLAEs at z = 6.6 and the remaining 5 as an active galactic nucleus at z = 6.6, two [O iii]λ5007 emitting galaxies at z = 0.84 and z = 0.85, and two nondetections. This emphasizes the need for full spectroscopic follow-up to determine accurate LFs. In constructing the ULLAE LF at z = 6.6, we combine our nine NEP ULLAEs with two previously discovered and confirmed ULLAEs in the COSMOS field: CR7 and COLA1. We apply rigorous corrections for incompleteness based on simulations. We compare our ULLAE LF at z = 6.6 with LFs at z = 5.7 and z = 6.6 from the literature. Our data reject some previous LF normalizations and power-law indices, but they are broadly consistent with others. Indeed, a comparative analysis of the different literature LFs suggests that no LF is fully consistent with any of the others, making it critical to determine the evolution from z = 5.7 to z = 6.6 using LFs constructed in exactly the same way at both redshifts.

Significant progress in the classification of Fermi unassociated sources has led to an increase in the number of blazars being found. The optical spectrum is effectively used to classify the blazars into two groups such as BL Lac objects and flat spectrum radio quasars (FSRQs). However, the accurate classification of the blazars without optical spectrum information, i.e., blazars of uncertain type (BCUs), remains a significant challenge. In this paper, we present a principle component analysis (PCA) and machine-learning hybrid blazars classification method. The method, based on the data from the Fermi-LAT 3FGL Catalog, first used the PCA to extract the primary features of the BCUs and then used a machine-learning algorithm to further classify the BCUs. Experimental results indicate that the use of PCA algorithms significantly improved the classification. More importantly, comparison with the Fermi-LAT 4FGL Catalog, which contains the spectral classification of those BCUs in the Fermi-LAT 3FGL Catalog, reveals that the proposed classification method in the study exhibits higher accuracy than currently established methods; specifically, 151 out of 171 BL Lac objects and 19 out of 24 FSRQs are correctly classified.

We investigate physical scaling laws for magnetic energy dissipation in solar flares, in the framework of the Sweet–Parker model and the Petschek model. We find that the total dissipated magnetic energy E_diss in a flare depends on the mean magnetic field component B_f associated with the free energy E_f, the length scale L of the magnetic area, the hydrostatic density scale height λ of the solar corona, the Alfvén Mach number M_A = v₁/v_A (the ratio of the inflow speed v₁ to the Alfvénic outflow speed v_A), and the flare duration τ_f, i.e., ${E}_{\mathrm{diss}}=(1/4\pi ){B}_{f}^{2}\ L\ \lambda \ {v}_{{\rm{A}}}\ {M}_{{\rm{A}}}\ {\tau }_{f}$, where the Alfvén speed depends on the nonpotential field strength B_np and the mean electron density n_e in the reconnection outflow. Using MDI/Solar Dynamics Observatory (SDO) and AIA/SDO observations and 3D magnetic field solutions obtained with the vertical-current approximation non-linear force-free field code we measure all physical parameters necessary to test scaling laws, which represents a new method to measure Alfvén Mach numbers M_A, the reconnection rate, and the total free energy dissipated in solar flares.

We report spatial distributions of the Fe–Kα line at 6.4 keV and the CO(J = 2–1) line at 230.538 GHz in NGC 2110, which are, respectively, revealed by Chandra and Atacama Large Millimeter/submillimeter Array (ALMA) at ≈05. A Chandra 6.2–6.5 keV to 3.0–6.0 keV image suggests that the Fe–Kα emission extends preferentially in a northwest to southeast direction out to ≈3'', or ∼500 pc, on each side. Spatially resolved spectral analyses support this by finding significant Fe–Kα emission lines only in the northwest and southeast regions. Moreover, their equivalent widths are found to be ∼1.5 keV, indicative for the fluorescence by nuclear X-ray irradiation as the physical origin. By contrast, CO(J = 2–1) emission is weak therein. For quantitative discussion, we derive ionization parameters by following an X-ray dominated region (XDR) model. We then find them high enough to interpret the weakness as the result of X-ray dissociation of CO and/or H₂. Another possibility also remains that CO molecules follow a superthermal distribution, resulting in brighter emission in higher-J lines. Further follow-up observations are encouraged to draw a conclusion on what predominantly changes the interstellar matter properties and whether the X-ray irradiation eventually affects the surrounding star formation as active galactic nucleus (AGN) feedback.

This paper reports the discovery of an Algol system KIC 10736223 that just passed the rapid mass transfer stage. From the light-curve and radial-velocity modeling we find KIC 10736223 to be a detached Algol system with the less-massive secondary nearly filling its Roche lobe. Based on the short-cadence Kepler data, we analyzed intrinsic oscillations of the pulsator and identified six secured independent δ Scuti-type pulsation modes (f₁, f₃, f₉, f₁₉, f₄₂, and f₄₈). We compute two grids of theoretical models to reproduce the δ Scuti frequencies, and find that fitting results of mass-accreting models agree well with those of single-star evolutionary models. The fundamental parameters of the primary star yielded with asteroseismology are $M={1.57}_{-0.09}^{+0.05}$M_⊙, Z = 0.009 ± 0.001, $R={1.484}_{-0.028}^{+0.016}$R_⊙, $\mathrm{log}g={4.291}_{-0.009}^{+0.004}$, ${T}_{\mathrm{eff}}={7748}_{-378}^{+230}$ K, and L = ${7.136}_{-1.519}^{+1.014}$L_⊙. The asteroseismic parameters match well with the dynamical parameters derived from the binary model. Moreover, our asteroseismic results show that the pulsator is an almost unevolved star with an age between 9.46 and 11.65 Myr for single-star evolutionary models and 2.67–3.14 Myr for mass-accreting models. Therefore, KIC 10736223 may be an Algol system that has just undergone the rapid mass-transfer process.

We present maps in several molecular emission lines of a 1 square degree region covering the W40 and Serpens South molecular clouds belonging to the Aquila Rift complex. The observations were made with the 45 m telescope at the Nobeyama Radio Observatory. We found that the ¹²CO and ¹³CO emission lines consist of several velocity components with different spatial distributions. The component that forms the main cloud of W40 and Serpens South, which we call the "main component," has a velocity of V_LSR ≃ 7 km s⁻¹. There is another significant component at V_LSR ≃  40 km s⁻¹, which we call the "40 km s⁻¹ component." The latter component is mainly distributed around two young clusters: W40 and Serpens South. Moreover, the two components look spatially anticorrelated. Such spatial configuration suggests that the star formation in W40 and Serpens South was induced by the collision of the two components. We also discuss a possibility that the 40 km s⁻¹ component consists of gas swept up by superbubbles created by SNRs and stellar winds from the Scorpius–Centaurus association.

In our quest to identify the progenitors of Type Ia supernovae (SNe Ia), we first update the nucleosynthesis yields for both near-Chandrasekhar- (Ch) and sub-Ch-mass white dwarfs (WDs) for a wide range of metallicities with our 2D hydrodynamical code and the latest nuclear reaction rates. We then include the yields in our galactic chemical evolution code to predict the evolution of elemental abundances in the solar neighborhood and dwarf spheroidal (dSph) galaxies Fornax, Sculptor, Sextans, and Carina. In the observations of the solar neighborhood stars, Mn shows an opposite trend to α elements, showing an increase toward higher metallicities, which is very well reproduced by the deflagration–detonation transition of Ch-mass WDs but never by double detonations of sub-Ch-mass WDs alone. The problem of Ch-mass SNe Ia was the Ni overproduction at high metallicities. However, we found that Ni yields of Ch-mass SNe Ia are much lower with the solar-scaled initial composition than in previous works, which keeps the predicted Ni abundance within the observational scatter. From the evolutionary trends of elemental abundances in the solar neighborhood, we conclude that the contribution of sub-Ch-mass SNe Ia to chemical enrichment is up to 25%. In dSph galaxies, however, larger enrichment from sub-Ch-mass SNe Ia than in the solar neighborhood may be required, which causes a decrease in [(Mg, Cr, Mn, Ni)/Fe] at lower metallicities. The observed high [Mn/Fe] ratios in Sculptor and Carina may also require additional enrichment from pure deflagrations, possibly as SNe Iax. Future observations of dSph stars will provide more stringent constraints on the progenitor systems and explosion mechanism of SNe Ia.

We recently developed an automated method, auto-GMM, to decompose simulated galaxies. It extracts kinematic structures in an accurate, efficient, and unsupervised way. We use auto-GMM to study the stellar kinematic structures of disk galaxies from the TNG100 run of IllustrisTNG. We identify four to five structures that are commonly present among the diverse galaxy population. Structures having strong to moderate rotation are defined as cold and warm disks, respectively. Spheroidal structures dominated by random motions are classified as bulges or stellar halos, depending on how tightly bound they are. Disky bulges are structures that have moderate rotation but compact morphology. Across all disky galaxies and accounting for the stellar mass within 3 half-mass radii, the kinematic spheroidal structures, obtained by summing up stars of bulges and halos, contribute ∼45% of the total stellar mass, while the disky structures constitute ∼55%. This study also provides important insights into the relationship between kinematically and morphologically derived galactic structures. Comparing the morphology of kinematic structures with that of traditional bulge+disk decomposition, we conclude that (1) the morphologically decomposed bulges are composite structures comprising a slowly rotating bulge, an inner halo, and a disky bulge; (2) kinematically disky bulges, akin to what are commonly called pseudo-bulges in observations, are compact disk-like components that have rotation similar to warm disks; (3) halos contribute almost 30% of the surface density of the outer part of morphological disks when viewed face on; and (4) both cold and warm disks are often truncated in central regions.

We measure rotation periods and sinusoidal amplitudes in Evryscope light curves for 122 two-minute K5–M4 TESS targets selected for strong flaring. The Evryscope array of telescopes has observed all bright nearby stars in the south, producing 2-minute cadence light curves since 2016. Long-term, high-cadence observations of rotating flare stars probe the complex relationship between stellar rotation, starspots, and superflares. We detect periods from 0.3487 to 104 days and observe amplitudes from 0.008 to 0.216 g' mag. We find that the Evryscope amplitudes are larger than those in TESS with the effect correlated to stellar mass (p-value = 0.01). We compute the Rossby number (R_o) and find that our sample selected for flaring has twice as many intermediate rotators (0.04 < R_o < 0.4) as fast (R_o < 0.04) or slow (R_o > 0.44) rotators; this may be astrophysical or a result of period detection sensitivity. We discover 30 fast, 59 intermediate, and 33 slow rotators. We measure a median starspot coverage of 13% of the stellar hemisphere and constrain the minimum magnetic field strength consistent with our flare energies and spot coverage to be 500 G, with later-type stars exhibiting lower values than earlier-type stars. We observe a possible change in superflare rates at intermediate periods. However, we do not conclusively confirm the increased activity of intermediate rotators seen in previous studies. We split all rotators at R_o ∼ 0.2 into bins of P_Rot < 10 days and P_Rot > 10 days to confirm that short-period rotators exhibit higher superflare rates, larger flare energies, and higher starspot coverage than do long-period rotators, at p-values of 3.2 × 10⁻⁵, 1.0 × 10⁻⁵, and 0.01, respectively.

Young moving groups (YMGs) are close (<100 pc), coherent collections of young (<100 Myr) stars that appear to have formed in the same star-forming molecular cloud. As such we would expect their individual initial mass functions (IMFs) to be similar to other star-forming regions, and by extension the Galactic field. Their close proximity to the Sun and their young ages means that YMGs are promising locations to search for young forming exoplanets. However, due to their low numbers of stars, stochastic sampling of the IMF means their stellar populations could vary significantly. We determine the range of planet-hosting stars (spectral types A, G, and M) possible from sampling the IMF multiple times, and find that some YMGs appear deficient in M-dwarfs. We then use these data to show that the expected probability of detecting terrestrial magma ocean planets is highly dependent on the exact numbers of stars produced through stochastic sampling of the IMF.

We present 1.3 mm ALMA dust polarization observations at a resolution of ∼0.02 pc for three massive molecular clumps, MM1, MM4, and MM9, in the infrared dark cloud G28.34+0.06. With these sensitive and high-resolution continuum data, MM1 is resolved into a cluster of condensations. The magnetic field structure in each clump is revealed by the polarized emission. We found a trend of decreasing polarized emission fraction with increasing Stokes I intensities in MM1 and MM4. Using the angular dispersion function method (a modified Davis–Chandrasekhar–Fermi method), the plane-of-sky magnetic field strengths in two massive dense cores, MM1-Core1 and MM4-Core4, are estimated to be ∼1.6 mG and ∼0.32 mG, respectively. The virial parameters in MM1-Core1 and MM4-Core4 are calculated to be ∼0.76 and ∼0.37, respectively, suggesting that massive star formation does not start in equilibrium. Using the polarization-intensity gradient-local gravity method, we found that the local gravity is closely aligned with intensity gradient in the three clumps, and the magnetic field tends to be aligned with the local gravity in MM1 and MM4 except for regions near the emission peak, which suggests that the gravity plays a dominant role in regulating the gas collapse. Half of the outflows in MM4 and MM9 are found to be aligned within 10° of the condensation-scale (<0.05 pc) magnetic field, indicating that the magnetic field could play an important role from condensation to disk scale in the early stage of massive star formation.

The intracluster medium of a galaxy cluster often shows an extended quasi-spiral structure, accentuated by tangential discontinuities known as cold fronts (CFs). These discontinuities are thought to isolate between low-entropy, high-metallicity gas inside (i.e., below) the CF that was lifted from the center of the cluster by some radial factor f_i and high-entropy, low-metallicity gas outside the CF that was pushed inward by a factor f_o. We find broad support for such a picture, by comparing the entropy and metallicity discontinuities with the respective azimuthal averages, using newly deprojected thermal profiles in clusters A2029, A2142, A2204, and Centaurus, supplemented by deprojected CFs from the literature. In particular, the mean advection factors f_K and f_Z, inferred from entropy and metallicity, respectively, strongly correlate (${ \mathcal R }={0.7}_{-0.3}^{+0.2}$) with each other, consistent with large-scale advection. However, unlike sloshing simulations, in which the inside/outside phases are an inflow/outflow settling back to equilibrium after a violent perturbation, our results are more consistent with an outflow/inflow, with the fast, Mach ${{ \mathcal M }}_{i}\sim 0.8$ gas inside the CF being a rapidly heated or mixed outflow, probably originating from the cD galaxy, and gas outside the CF being an ${{ \mathcal M }}_{o}\sim 0.03$, slowly cooling inflow. In particular, entropy indicates an outside advection factor $1.3\,\lesssim$f_Ko$\lesssim 1.5$ that is approximately constant in all CFs, gauging the distance traversed by inflowing gas within a cooling time. In contrast, $1.1\lesssim {f}_{{Ki}}\lesssim 2.5$ and $1\lesssim {f}_{Z}\lesssim 17$ vary considerably among clusters and strongly correlate ($3.1\sigma {\rm{\mbox{--}}}4.2\sigma$) with the virial mass, ${f}_{{Ki}}\propto {M}_{200}^{0.14\pm 0.07}$ and ${f}_{Z}\propto {M}_{200}^{1.4\pm 0.4}$, suggesting that each cluster sustains a quasi-steady spiral flow.

The main goal of this study is to determine the solar origin of four single shocks observed at the Lagrange point L1 and followed by storm sudden commencements (SSCs) during 2002. We look for associated coronal mass ejections (CMEs), starting from estimates of the transit time from Sun to Earth. For each CME, we investigate its association with a radio type II burst, an indicator of the presence of a shock wave. For three of the events, the type II burst is shown to propagate along the same, or a similar, direction as the fastest segment of the CME leading edge. We analyze for each event the role of the coronal environment in the CME development, the shock formation, and their propagation, to finally identify its complex evolution. The ballistic velocity of these shocks during their propagation from the corona to L1 is compared to the shock velocity at L1. Based on a detailed analysis of the shock propagation and possible interactions up to 30 solar radii, we find a coherent velocity evolution for each event, in particular for one event, the 2002 April 14 SSC, for which a previous study did not find a satisfactory CME source. For the other three events, we observe the formation of a white-light shock overlying the different sources associated with those events. The localization of the event sources over the poles, together with an origin of the shocks being due to encounters of CMEs, can explain why at L1 we observe only single shocks and not interplanetary CMEs.

We present the discovery of WISEA J083011.95+283716.0, the first Y-dwarf candidate identified through the "Backyard Worlds: Planet 9" citizen science project. We identified this object as a red, fast-moving source with a faint W2 detection in multiepoch AllWISE and unWISE images. We have characterized this object with Spitzer  and Hubble Space Telescope's (HST) follow-up imaging. With mid-infrared detections in Spitzer's ch1 and ch2 bands and flux upper limits in HST F105W and F125W filters, we find that this object is both very faint and has extremely red colors (ch1 − ch2 = 3.25 ± 0.23 mag, F125W − ch2 ≥ 9.36 mag), consistent with a T_eff ∼ 300 K source, as estimated from the known Y-dwarf population. A preliminary parallax provides a distance of ${11.1}_{-1.5}^{+2.0}$ pc, leading to a slightly warmer temperature of ∼350 K. The extreme faintness and red HST  and Spitzer  colors of this object suggest that it may be a link between the broader Y-dwarf population and the coldest known brown dwarf WISE J0855−0714, and may highlight our limited knowledge of the true spread of Y-dwarf colors. We also present four additional "Backyard Worlds: Planet 9" late-T brown dwarf discoveries within 30 pc.

We present a study on the radial profiles of the D4000, luminosity-weighted stellar ages τ_L, and luminosity-weighted stellar metallicities [Z/H]_L of 3654 nearby galaxies (0.01 < z < 0.15) using the IFU spectroscopic data from the MaNGA survey available in the SDSS DR15, in an effort to explore the connection between median stellar population radial gradients (i.e., ∇D4000, ∇τ_L, ∇[Z/H]_L) out to ∼1.5 R_e and various galaxy properties, including stellar mass (M_⋆), specific star formation rate (sSFR), morphologies, and local environment. We find that M_⋆ is the single most predictive physical property for ∇D4000 and ∇[Z/H]_L. The most predictive properties for ∇τ_L are sSFR and, to a lesser degree, M_⋆. The environmental parameters, including local galaxy overdensities and central–satellite division, have virtually no correlation with stellar population radial profiles for the whole sample, but the ∇D4000 of star-forming satellite galaxies with M_⋆ ≲ 10¹⁰M_⊙ exhibit a significant positive correlation with galaxy overdensities. Galaxies with lower sSFR have on average steeper negative stellar population gradients, and this sSFR dependence is stronger for more massive star-forming galaxies. The negative correlation between the median stellar population gradients and M_⋆ are best described largely as segmented relationships, whereby median gradients of galaxies with log M_⋆ ≲ 10.0 (with the exact value depending on sSFR) have much weaker mass dependence than galaxies with higher M_⋆. While the dependence of the radial gradients of ages and metallicities on T-Types and central stellar mass surface densities are generally not significant, galaxies with later T-Types or lower central mass densities tend to have significantly lower D4000, younger τ_L, and lower [Z/H]_L across the radial ranges probed in this study.

In contrast to massive galaxies with solar or super-solar gas phase metallicities, very few active galactic nuclei (AGNs) are found in low-metallicity dwarf galaxies. Such a population could provide insight into the origins of supermassive black holes. Here we report near-IR spectroscopic and X-ray observations of SDSS J105621.45+313822.1, a low-mass, low-metallicity galaxy with optical narrow line ratios consistent with star-forming galaxies but a broad Hα line and mid-infrared colors consistent with an AGN. We detect the [Si vi] 1.96 μm coronal line and a broad Paα line with an FWHM of 850 ± 25 km s⁻¹. Together with the optical broad lines and coronal lines seen in the Sloan Digital Sky Survey (SDSS) spectrum, we confirm the presence of a highly accreting black hole with mass (2.2 ± 1.3) × 10⁶M_⊙, with a bolometric luminosity of ≈10⁴⁴ erg s⁻¹ based on the coronal line luminosity, implying a highly accreting AGN. Chandra observations reveal a weak nuclear point source with ${L}_{{\rm{X}},2\mbox{--}10\mathrm{keV}}=(2.3\pm 1.2)\times {10}^{41}$ erg s⁻¹, ∼2 orders of magnitude lower than that predicted by the mid-infrared luminosity, suggesting that the AGN is highly obscured despite showing broad lines in the optical spectrum. The low X-ray luminosity and optical narrow line ratios of J1056+3138 highlight the limitations of commonly employed diagnostics in the hunt for AGNs in the low-metallicity, low-mass regime.