Table of contents

The tomographic Alcock–Paczynski (AP) method is so far the best method in separating the AP signal from the redshift space distortion (RSD) effects and deriving powerful constraints on cosmological parameters using the $\lesssim 40\,{h}^{-1}\ \mathrm{Mpc}$ clustering region. To guarantee that the method can be easily applied to the future large-scale structure surveys, we study the possibility of estimating the systematics of the method using the fast simulation method. The major contribution of the systematics comes from the nonzero redshift evolution of the RSD effects, which is quantified by ${\hat{\xi }}_{{\rm{\Delta }}s}(\mu ,z)$ in our analysis, and estimated using the BigMultidark exact N-body simulation and approximate COmoving Lagrangian Acceleration (COLA) simulation samples. We find about 5%/10% evolution when comparing the ${\hat{\xi }}_{{\rm{\Delta }}s}(\mu ,z)$ measured as z = 0.5/z = 1 to the measurements at z = 0. We checked the inaccuracy in the 2pCFs computed using COLA, and find it 5–10 times smaller than the intrinsic systematics of the tomographic AP method, indicating that using COLA to estimate the systematics is good enough. Finally, we test the effect of halo bias, and find ≲1.5% change in ${\hat{\xi }}_{{\rm{\Delta }}s}$ when varying the halo mass within the range of 2 × 10¹²–10¹⁴M_⊙. We will perform more studies to achieve an accurate and efficient estimation of the systematics in the redshift range of z = 0–1.5.

The observed mass–radius relationship of low-mass planets informs our understanding of their composition and evolution. Recent discoveries of low-mass, large-radius objects ("super-puffs") have challenged theories of planet formation and atmospheric loss, as their high inferred gas masses make them vulnerable to runaway accretion and hydrodynamic escape. Here we propose that high-altitude photochemical hazes could enhance the observed radii of low-mass planets and explain the nature of super-puffs. We construct model atmospheres in radiative-convective equilibrium and compute rates of atmospheric escape and haze distributions, taking into account haze coagulation, sedimentation, diffusion, and advection by an outflow wind. We develop mass–radius diagrams that include atmospheric lifetimes and haze opacity, which is enhanced by the outflow, such that young (∼0.1–1 Gyr), warm (T_eq ≥ 500 K), low-mass objects (M_c < 4 M_⊕) should experience the most apparent radius enhancement due to hazes, reaching factors of three. This reconciles the densities and ages of the most extreme super-puffs. For Kepler-51b, the inclusion of hazes reduces its inferred gas mass fraction to <10%, similar to that of planets on the large-radius side of the sub-Neptune radius gap. This suggests that Kepler-51b may be evolving toward that population and that some warm sub-Neptunes may have evolved from super-puffs. Hazes also render transmission spectra of super-puffs and sub-Neptunes featureless, consistent with recent measurements. Our hypothesis can be tested by future observations of super-puffs' transmission spectra at mid-infrared wavelengths, where we predict that the planet radius will be half of that observed in the near-infrared.

We present a 7 minute long 4π-3D simulation of a shell merger event in a nonrotating 18.88 ${M}_{\odot }$ supernova progenitor before the onset of gravitational collapse. The key motivation is to capture the large-scale mixing and asymmetries in the wake of the shell merger before collapse using a self-consistent approach. The 4π geometry is crucial, as it allows us to follow the growth and evolution of convective modes on the largest possible scales. We find significant differences between the kinematic, thermodynamic, and chemical evolution of the 3D and 1D models. The 3D model shows vigorous convection leading to more efficient mixing of nuclear species. In the 3D case, the entire oxygen shell attains convective Mach numbers of ≈0.1, whereas in the 1D model, the convective velocities are much lower, and there is negligible overshooting across convective boundaries. In the 3D case, the convective eddies entrain nuclear species from the neon (and carbon) layers into the deeper part of the oxygen-burning shell, where they burn and power a violent convection phase with outflows. This is a prototypical model of a convective–reactive system. Due to the strong convection and resulting efficient mixing, the interface between the neon layer and the silicon-enriched oxygen layer disappears during the evolution, and silicon is mixed far out into the merged oxygen/neon shell. Neon entrained inward by convective downdrafts burns, resulting in lower neon mass in the 3D model compared to the 1D model at the time of collapse. In addition, the 3D model develops remarkable large-scale, large-amplitude asymmetries, which may have important implications for the impending gravitational collapse and subsequent explosion.

The nitriles present in the atmosphere of Titan can be expected to exhibit different ${}^{14}{\rm{N}}/{}^{15}{\rm{N}}$ values depending on their production processes, primarily because of the various ${{\rm{N}}}_{2}$ dissociation processes induced by different sources such as ultraviolet radiation, magnetospheric electrons, and Galactic cosmic rays. For ${\mathrm{CH}}_{3}\mathrm{CN}$, one photochemical model predicted a ¹⁴N/¹⁵N value of 120–130 in the lower stratosphere. This is much higher than that for HCN and ${\mathrm{HC}}_{3}{\rm{N}}$, ∼67–94. By analyzing archival data obtained by the Atacama Large Millimeter/submillimeter Array, we successfully detected submillimeter rotational transitions of ${\mathrm{CH}}_{3}{{\rm{C}}}^{15}{\rm{N}}$ (J = 19–18) located in the 338 GHz band in Titan's atmospheric spectra. By comparing those observations with the simultaneously observed ${\mathrm{CH}}_{3}\mathrm{CN}$ (J = 19–18) lines in the 349 GHz band, which probe from 160 to ∼400 km altitude, we then derived ¹⁴N/¹⁵N in ${\mathrm{CH}}_{3}\mathrm{CN}$ as 125${}_{-44}^{+145}$. Although the range of the derived value shows insufficient accuracy due to limitations on data quality, the best-fit value suggests that ¹⁴N/¹⁵N for ${\mathrm{CH}}_{3}\mathrm{CN}$ is higher than values that have previously been observed and theoretically predicted for HCN and ${\mathrm{HC}}_{3}{\rm{N}}$. This may be explained by the different ${{\rm{N}}}_{2}$ dissociation sources according to altitude, as suggested by a recent photochemical model.

Penumbral transient brightening events have been attributed to magnetic reconnection episodes occurring in the low corona. We investigated the trigger mechanism of these events in active region NOAA 12546 by using multiwavelength observations obtained with the Interferometric Bidimensional Spectrometer, by the Solar Dynamics Observatory, the Interface Region Imaging Spectrograph, and the Hinode satellites. We focused on the evolution of an area of the penumbra adjacent to two small-scale emerging flux regions (EFRs), which manifested three brightening events detected from the chromosphere to the corona. Two of these events correspond to B-class flares. The same region showed short-lived moving magnetic features (MMFs) that streamed out from the penumbra. In the photosphere, the EFRs led to small-scale penumbral changes associated with a counter-Evershed flow and to a reconfiguration of the magnetic fields in the moat. The brightening events had one of the footpoints embedded in the penumbra and seemed to result from the distinctive interplay between the preexisting penumbral fields, MMFs, and the EFRs. The IRIS spectra measured therein reveal enhanced temperature and asymmetries in spectral lines, suggestive of event triggering at different heights in the atmosphere. Specifically, the blue asymmetry noted in C ii and Mg ii h&k lines suggests the occurrence of chromospheric evaporation at the footpoint located in the penumbra as a consequence of the magnetic reconnection process at higher atmospheric heights.

We report on variability and correlation studies using multiwavelength observations of the blazar Mrk 421 during the month of 2010 February, when an extraordinary flare reaching a level of ∼27 Crab Units above 1 TeV was measured in very high energy (VHE) γ-rays with the Very Energetic Radiation Imaging Telescope Array System (VERITAS) observatory. This is the highest flux state for Mrk 421 ever observed in VHE γ-rays. Data are analyzed from a coordinated campaign across multiple instruments, including VHE γ-ray (VERITAS, Major Atmospheric Gamma-ray Imaging Cherenkov), high-energy γ-ray (Fermi-LAT), X-ray (Swift, Rossi X-ray Timing Experiment, MAXI), optical (including the GASP-WEBT collaboration and polarization data), and radio (Metsähovi, Owens Valley Radio Observatory, University of Michigan Radio Astronomy Observatory). Light curves are produced spanning multiple days before and after the peak of the VHE flare, including over several flare "decline" epochs. The main flare statistics allow 2 minute time bins to be constructed in both the VHE and optical bands enabling a cross-correlation analysis that shows evidence for an optical lag of ∼25–55 minutes, the first time-lagged correlation between these bands reported on such short timescales. Limits on the Doppler factor (δ ≳ 33) and the size of the emission region (${\delta }^{-1}{R}_{B}\lesssim 3.8\times {10}^{13}\,{\rm{cm}}$) are obtained from the fast variability observed by VERITAS during the main flare. Analysis of 10 minute binned VHE and X-ray data over the decline epochs shows an extraordinary range of behavior in the flux–flux relationship, from linear to quadratic to lack of correlation to anticorrelation. Taken together, these detailed observations of an unprecedented flare seen in Mrk 421 are difficult to explain with the classic single-zone synchrotron self-Compton model.

As we are heading toward the next solar cycle, presumably with a relatively small amplitude, it is of significant interest to reconstruct and describe the past secular minima on the basis of actual observations at the time. The Dalton Minimum is often considered one of the secular minima captured in the coverage of telescopic observations. Nevertheless, the reconstructions of the sunspot group number vary significantly, and the existing butterfly diagrams have a large data gap during the period. This is partially because most long-term observations at that time have remained unexplored in historical archives. Therefore, to improve our understanding on the Dalton Minimum, we have located two series of Thaddäus Derfflinger's observational records spanning 1802–1824 (a summary manuscript and logbooks), as well as his Brander's 5.5 feet azimuthal quadrant preserved in the Kremsmünster Observatory. We have revised the existing Derfflinger's sunspot group number with Waldmeier classification, and eliminated all the existing "spotless days" to remove contaminations from solar elevation observations. We have reconstructed the butterfly diagram on the basis of his observations and illustrated sunspot distributions in both solar hemispheres. Our article aims to revise the trend of Derfflinger's sunspot group number and to bridge a data gap of the existing butterfly diagrams around the Dalton Minimum. Our results confirm that the Dalton Minimum is significantly different from the Maunder Minimum, both in terms of cycle amplitudes and sunspot distributions. Therefore, the Dalton Minimum is more likely a secular minimum in the long-term solar activity, while further investigations for the observations at that time are required.

The observed internal plateau of X-ray emission in some short gamma-ray bursts (GRBs) suggests the formation of a remnant supramassive magnetar following a double neutron star (NS) merger. In this paper, we assume that the rotational energy is lost mainly via gravitational-wave radiation instead of magnetic dipole (MD) radiation, and present further constraints on the NS nuclear equation of state (EoS) via mass quadrupole deformation and r-mode fluid oscillations of the magnetar. We present two short GRBs with measured redshifts, 101219A and 160821B, whose X-ray light curves exhibit an internal plateau. This suggests that a supramassive NS may survive as the central engine. By considering 12 NS EoSs, within the mass quadrupole deformation scenario we find that the GM1, DD2, and DDME2 models give an M_p band falling within the 2σ region of the proto-magnetar mass distribution for ε = 0.01. This is consistent with the constraints from the MD radiation dominated model of rotational energy loss. However, for an r-mode fluid oscillation model with α = 0.1 the data suggest that the NS EOS is close to the Shen and APR models, which is obviously different from the MD radiation dominated and mass quadrupole deformation cases.

Coronal rain is ubiquitous in flare loops, forming shortly after the onset of the solar flare. Rain is thought to be caused by a thermal instability, a localized runaway cooling of material in the corona. The models that demonstrate this require extremely long duration heating on the order of the radiative cooling time, localized near the footpoints of the loops. In flares, electron beams are thought to be the primary energy transport mechanism, driving strong footpoint heating during the impulsive phase that causes evaporation, filling and heating flare loops. Electron beams, however, do not act for a long period of time, and even supposing that they did, their heating would not remain localized at the footpoints. With a series of numerical experiments, we show directly that these two issues mean that electron beams are incapable of causing the formation of rain in flare loops. This result suggests that either there is another mechanism acting in flare loops responsible for rain, or that the modeling of the cooling of flare loops is somehow deficient. To adequately describe flares, the standard model must address this issue to account for the presence of coronal rain.

Interplanetary coronal mass ejections (ICMEs) are the counterparts of coronal mass ejections (CMEs) that extend in the interplanetary (IP) space and interact with the underlying solar wind (SW). ICMEs and their corresponding shocks can sweep out galactic cosmic rays (GCRs) and thus modulate their intensity, resulting in non-recurrent Forbush decreases (FDs). In this work, we selected all FDs that were associated with a sudden storm commencement (SSC) at Earth, and a solar driver (e.g., CME) was clearly identified as the ICME's source. We introduce and employ the t_H parameter, which is the time delay (in hours) of the maximum strength of the interplanetary magnetic field from the FD onset (as is marked via the SSC), and consequently derive three groups of FD events (i.e., the early, medium, and late ones). For each of these we examine the mean characteristics of the FDs and the associated IP variations per group, as well as the resulting correlations. In addition, we demonstrate the outputs of a superposed epoch analysis, which led to an average time profile of the resulting FDs and the corresponding IP variations, per group. Finally, we interpret our results based on the theoretical expectations for the FD phenomenon. We find that both the shock sheath and the ejecta are necessary for deep GCR depressions and that the FD amplitude (A0) is larger for faster-propagating ICMEs. Additionally, we note the importance of the turbulent shock-sheath region across all groups. Finally, we present empirical relations connecting A0 to SW properties.

The joint detection of GW170817 and GRB 170817A indicated that at least a fraction of short gamma-ray bursts (SGRBs) originate from binary neutron star (BNS) mergers. One possible remnant of a BNS merger is a rapidly rotating, strongly magnetized neutron star, which has been discussed as one possible central engine for gamma-ray bursts. For a rapidly rotating magnetar central engine, the deposition of the rotation energy into the ejecta launched from the merger could lead to bright radio emission. The brightness of radio emission years after an SGRB would provide an estimate of the kinetic energy of ejecta and, hence, a possible constraint on the BNS merger product. We perform a more detailed calculation on the brightness of radio emission from the interaction between the merger ejecta and circumburst medium in the magnetar scenario, invoking several important physical processes such as generic hydrodynamics, relativistic effects, and the deep Newtonian phase. We use the model to constrain the allowed parameter space for 15 SGRBs that have late radio observations. Our results show that an injection energy of E_inj ∼ 10⁵² erg is allowed for all the cases, which suggests that the possibility of a supramassive or hypermassive neutron star remnant is not disfavored by the available radio data.

For a better understanding of the magnetic field in the solar corona and dynamic activities such as flares and coronal mass ejections, it is crucial to measure the time-evolving coronal field and accurately estimate the magnetic energy. Recently, a new modeling technique called the data-driven coronal field model, in which the time evolution of magnetic field is driven by a sequence of photospheric magnetic and velocity field maps, has been developed and revealed the dynamics of flare-productive active regions. Here we report on the first qualitative and quantitative assessment of different data-driven models using a magnetic flux emergence simulation as a ground-truth (GT) data set. We compare the GT field with those reconstructed from the GT photospheric field by four data-driven algorithms. It is found that, at minimum, the flux rope structure is reproduced in all coronal field models. Quantitatively, however, the results show a certain degree of model dependence. In most cases, the magnetic energies and relative magnetic helicity are comparable to or at most twice of the GT values. The reproduced flux ropes have a sigmoidal shape (consistent with GT) of various sizes, a vertically standing magnetic torus, or a packed structure. The observed discrepancies can be attributed to the highly non-force-free input photospheric field, from which the coronal field is reconstructed, and to the modeling constraints such as the treatment of background atmosphere, the bottom boundary setting, and the spatial resolution.

Chandra X-ray observations of Kepler's supernova remnant indicate the existence of a high-speed Fe-rich ejecta structure in the southwestern region. We report strong K-shell emission from Fe-peak elements (Cr, Mn, Fe, Ni), as well as Ca, in this Fe-rich structure, implying that those elements could be produced in the inner area of the exploding white dwarf. We found Ca/Fe, Cr/Fe, Mn/Fe, and Ni/Fe mass ratios of 1.0%–4.1%, 1.0%–4.6%, 1%–11%, and 2%–30%, respectively. In order to constrain the burning regime that could produce this structure, we compared these observed mass ratios with those in 18 one-dimensional Type Ia nucleosynthesis models (including both near-M_Ch and sub-M_Ch explosion models). The observed mass ratios agree well with those around the middle layer of incomplete Si burning in Type Ia nucleosynthesis models with a peak temperature of ∼(5.0–5.3) × 10⁹ K and a high metallicity, Z > 0.0225. Based on our results, we infer the necessity for some mechanism to produce protruding Fe-rich clumps dominated by incomplete Si-burning products during the explosion. We also discuss the future perspectives of X-ray observations of Fe-rich structures in other Type Ia supernova remnants.

We describe the goals and first results of the Program for Imaging of the PERseus cluster of galaxies (PIPER). The first phase of the program builds on imaging of fields obtained with the Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS)/WFC and WFC3/UVIS cameras. Our PIPER target fields with HST include major early-type galaxies including the active central giant NGC 1275, known ultra-diffuse galaxies, and the intracluster medium. The resulting two-color photometry in F475W and F814W reaches deep enough to resolve and measure the globular cluster (GC) populations in the Perseus member galaxies. Here we present initial results for eight pairs of outer fields that confirm the presence of intergalactic GCs (IGCs) in fields as distant as 740 kpc from the Perseus center (40% of the virial radius of the cluster). Roughly 90% of these IGCs are identifiably blue (metal-poor) but there is a clear trace of a red (metal-rich) component as well, even at these very remote distances.

WISEA J080822.18–644357.3, an M star in the Carina association, exhibits extreme infrared excess and accretion activity at an age greater than the expected accretion disk lifetime. We consider J0808 as the prototypical example of a class of M star accretion disks at ages ≳20 Myr, which we call "Peter Pan" disks, because they apparently refuse to grow up. We present four new Peter Pan disk candidates identified via the Disk Detective citizen science project, coupled with Gaia astrometry. We find that WISEA J044634.16–262756.1 and WISEA J094900.65–713803.1 both exhibit significant infrared excess after accounting for nearby stars within the Two Micron All Sky Survey (2MASS) beams. The J0446 system has >95% likelihood of Columba membership. The J0949 system shows >95% likelihood of Carina membership. We present new Gemini Multi-Object Spectrograph optical spectra of all four objects, showing possible accretion signatures on all four stars. We present ground-based and TESS light curves of J0808 and 2MASS J0501–4337, including a large flare and aperiodic dipping activity on J0808, and strong periodicity on J0501. We find Paβ and Brγ emission indicating ongoing accretion in near-IR spectroscopy of J0808. Using observed characteristics of these systems, we discuss mechanisms that lead to accretion disks at ages ≳20 Myr, and find that these objects most plausibly represent long-lived CO-poor primordial disks, or "hybrid" disks, exhibiting both debris and primordial-disk features. The question remains: why have gas-rich disks persisted so long around these particular stars?

Water worlds are water-rich (>1 wt% H₂O) exoplanets. The classical models of water worlds considered layered structures determined by the phase boundaries of pure water. However, water worlds are likely to possess comet-like compositions, with between ∼3 and 30 mol% CO₂ relative to water. In this study, we build an interior structure model of habitable (i.e., surface liquid ocean–bearing) water worlds using the latest results from experimental data on the CO₂–H₂O system to explore the CO₂ budget and localize the main CO₂ reservoirs inside of these planets. We show that CO₂ dissolved in the ocean and trapped inside of a clathrate layer cannot accommodate a cometary amount of CO₂ if the planet accretes more than 11 wt% of volatiles (CO₂ + H₂O) during its formation. If the atmosphere holds more than a negligible amount of the CO₂ (>0.01% of the planet mass), the planet will not have a habitable surface temperature. We propose a new, potentially dominant, CO₂ reservoir for water worlds: CO₂ buried inside of the high-pressure water ice mantle as CO₂ ices or (H₂CO₃ · H₂O), the monohydrate of carbonic acid. If insufficient amounts of CO₂ are sequestered in either this reservoir or the planet's iron core, habitable-zone water worlds could generically be stalled in their cooling before liquid oceans have a chance to condense.

An ensemble of inspiraling supermassive black hole binaries should produce a stochastic background of very low frequency gravitational waves. This stochastic background is predicted to be a power law, with a gravitational-wave strain spectral index of −2/3, and it should be detectable by a network of precisely timed millisecond pulsars, widely distributed on the sky. This paper reports a new "time slicing" analysis of the 11 yr data release from the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) using 34 millisecond pulsars. Methods to flag potential "false-positive" signatures are developed, including techniques to identify responsible pulsars. Mitigation strategies are then presented. We demonstrate how an incorrect noise model can lead to spurious signals, and we show how independently modeling noise across 30 Fourier components, spanning NANOGrav's frequency range, effectively diagnoses and absorbs the excess power in gravitational-wave searches. This results in a nominal, and expected, progression of our gravitational-wave statistics. Additionally, we show that the first interstellar medium event in PSR J1713+0747 pollutes the common red-noise process with low spectral index noise, and we use a tailored noise model to remove these effects.

The field of solar magnetoseismology (SMS) is heavily reliant upon our understanding of magnetohydrodynamic (MHD) waves that occur in many solar features. Building on previous studies of propagating MHD waves in a magnetic slab embedded in a nonmagnetic asymmetric environment, in this study we assume a line-tying boundary condition and use analytical techniques to derive the dispersion relation for linear standing MHD oscillations. The slab is first assumed thin, with arbitrary asymmetry, in order to derive the frequencies of the standing harmonic modes for both slow quasi-sausage and slow quasi-kink waves. Besides this, the asymmetry is assumed to be weak in order to determine the frequency dependence on the width of the slab and the asymmetry of the system, to leading order. For both the quasi-sausage and quasi-kink modes, the derived eigenfrequencies show that the dependence on the asymmetry in the system is much weaker than the dependence on the width of the slab. Using the eigenfrequencies, other observable quantities are derived (such as, e.g., the frequency ratio) providing an opportunity to use SMS to infer background diagnostics of the system.

We apply Noether's theorem to observations of main-sequence stars from the Gaia Data Release 2 archive to probe the matter distribution function of the Galaxy. That is, we examine the axial symmetry of stars at vertical heights z, $0.2\leqslant | z| \leqslant 3\,\mathrm{kpc}$, to probe the quality of the angular momentum L_z as an integral of motion. The failure of this symmetry test would speak to a Milky Way, in both its visible and dark matter, that is not isolated and/or not in steady state. The left–right symmetry-breaking pattern we have observed, north and south, reveals both effects, with a measured deviation from symmetry of typically 0.5%. We show that a prolate form of the gravitational distortion of the Milky Way by the Large Magellanic Cloud, determined from fits to the Orphan stream by Erkal et al., is compatible with the size and sign of the axial-symmetry-breaking effects we have discovered in our sample of up to 14.4 million main-sequence stars, speaking to a distortion of an emergent, rather than static, nature.

We present two searches for IceCube neutrino events coincident with 28 fast radio bursts (FRBs) and 1 repeating FRB. The first improves on a previous IceCube analysis—searching for spatial and temporal correlation of events with FRBs at energies greater than roughly 50 GeV—by increasing the effective area by an order of magnitude. The second is a search for temporal correlation of MeV neutrino events with FRBs. No significant correlation is found in either search; therefore, we set upper limits on the time-integrated neutrino flux emitted by FRBs for a range of emission timescales less than one day. These are the first limits on FRB neutrino emission at the MeV scale, and the limits set at higher energies are an order-of-magnitude improvement over those set by any neutrino telescope.

There are several ongoing projects to search for stars orbiting around an invisible companion. A fraction of such candidates may be a triple, instead of a binary, consisting of an inner binary black hole (BBH) and an outer orbiting star. In this paper, we propose a methodology to search for a signature of such an inner BBH, possibly a progenitor of gravitational-wave sources discovered by LIGO, from the precise radial velocity (RV) follow-up of the outer star. We first describe a methodology using an existing approximate RV formula for coplanar circular triples. We apply this method and constrain the parameters of a possible inner binary object in 2M05215658+4359220, which consists of a red giant and an unseen companion. Next we consider coplanar but non-circular triples. We compute numerically the RV variation of a tertiary star orbiting around an inner BBH, generate mock RV curves, and examine the feasibility of detection of the BBH for our fiducial models. We conclude that short-cadence RV monitoring of a star–BH binary provides an interesting and realistic method to constrain and/or search for possible inner BBHs. Indeed a recent discovery of the star–BH binary system LB-1 may imply that there are a large number of such unknown objects in our Galaxy, which are ideal targets for the methodology proposed here.

A 70 ${M}_{\odot }$ black hole (BH) was discovered in the Milky Way disk in a long-period detached binary system (LB-1) with a high-metallicity 8 ${M}_{\odot }$ B star companion. Current consensus on the formation of BHs from high-metallicity stars limits the BH mass to be below 20 ${M}_{\odot }$ due to strong mass loss in stellar winds. Using analytic evolutionary formulae, we show that the formation of a 70 ${M}_{\odot }$ BH in a high-metallicity environment is possible if wind mass-loss rates are reduced by factor of five. As observations indicate, a fraction of massive stars have surface magnetic fields that may quench the wind mass-loss, independently of stellar mass and metallicity. We confirm such a scenario with detailed stellar evolution models. A nonrotating 85 ${M}_{\odot }$ star model at Z = 0.014 with decreased winds ends up as a 71 ${M}_{\odot }$ star prior to core collapse with a 32 ${M}_{\odot }$ He core and a 28 ${M}_{\odot }$ CO core. Such a star avoids the pair-instability pulsation supernova mass loss that severely limits BH mass and may form a ∼70 ${M}_{\odot }$ BH in the direct collapse. Stars that can form 70 ${M}_{\odot }$ BHs at high Z expand to significant sizes, with radii of R ≳ 600 ${R}_{\odot }$, however, exceeding the size of the LB-1 orbit. Therefore, we can explain the formation of BHs up to 70 ${M}_{\odot }$ at high metallicity and this result is valid whether or not LB-1 hosts a massive BH. However, if LB-1 hosts a massive BH we are unable to explain how such a binary star system could have formed without invoking some exotic scenarios.

Dipolarization fronts (DFs) of magnetic reconnection are a transient field structure accompanied with a sharp increase of magnetic field component normal to plasma sheet and a high-speed plasma flow. The thermodynamics of DFs in the anisotropic plasma, which have not been studied so far, are investigated in this paper using two-dimensional, resistive magnetohydrodynamic simulations with double-polytropic energy laws in which two polytropic exponents, γ_∥ and ${\gamma }_{\perp }$, are used as parameters to describe various thermodynamic conditions. The subscripts ∥ and $\perp$ denote, respectively, directions parallel and perpendicular to the local magnetic field. Four different types of DFs observed by the Magnetospheric Multiscale Mission (MMS) in the plasma sheet of the Earth's magnetotail are presented—namely, (1) both temperatures T_∥ and ${T}_{\perp }$ decrease; (2) both T_∥ and ${T}_{\perp }$ increase; (3) T_∥ decreases while ${T}_{\perp }$ increases; (4) T_∥ increases while ${T}_{\perp }$ decreases. By using four different pairs of γ_∥ and ${\gamma }_{\perp }$, these four types of DFs can be reproduced, where the thermodynamics of Type-4 DF may correspond to the double-adiabatic Chew–Goldberger–Low conditions. It is concluded that the thermodynamic condition is seen to resemble most closely an adiabatic process for Type-1, -2, and -4 DFs, but to an isothermal process for Type-3 DF.

The Interface Region Imaging Spectrograph (IRIS) Mg ii k line serves as a very good tool to diagnose the heating processes in solar flares. Recent studies have shown that apart from the usual red asymmetries that are interpreted as the result of condensation downflows, this line could also show a blue-wing enhancement. To investigate how such a blue asymmetry is formed, we perform a grid of radiative hydrodynamic simulations and calculate the corresponding line profiles. We find that such a spectral feature is likely to originate from the upward plasma motion in the upper chromosphere. However, the formation region that is responsible for the blue-wing enhancement could be located in an evaporation region, in an upward-moving blob, and even an upward-moving condensation region. We discuss how the electron beam parameters affect these different dynamics of the atmosphere.

Numerical simulations of radiative two-temperature hot accretion flows (HAFs) around Neutron stars (NSs) are performed. We assume that all of the energy carried by the HAF around a NS will be thermalized and radiated out at the surface of the NS. The thermal photons will propagate outwards radially and cool the HAF via Comptonization. We define $\dot{m}$ as the mass accretion rate at the surface of the central object in unit of Eddington accretion rate (${\dot{M}}_{\mathrm{Edd}}=10{L}_{\mathrm{Edd}}/{c}^{2}$, with L_Edd and c being Eddington luminosity and speed of light, respectively). When $\dot{m}$ is lower than ∼10⁻⁴, the cooling of the HAF is not important and outflows are very strong. When $\dot{m}\gt \sim {10}^{-3}$, cooling becomes important and outflows are significantly weak. In the range ${10}^{-4}\lt \dot{m}\lt {10}^{-3}$, the HAFs transients from a strong outflow phase to a very weak outflow phase with increase of $\dot{m}$. The properties of the HAF around a NS are also compared with those of the HAF around a BH. We find that with a similar $\dot{m}$, the dynamical properties of the HAF around a NS are quite similar as those of the HAF around a BH. However, the emitted spectrum of a HAF around a NS can be quite different from that of a HAF around a BH due to the presence of a thermal soft X-ray component coming from the surface of the NS.

About 20% of stars in the solar vicinity are in the Hercules stream, a bundle of stars that move together with a velocity distinct from the Sun. Its origin is still uncertain. Here, we explore the possibility that Hercules is made of trojans, stars captured at L4, one of the Lagrangian points of the stellar bar. Using GALAKOS–a high-resolution N-body simulation of the Galactic disk–we follow the motions of stars in the corotating frame of the bar and confirm previous studies on Hercules being formed by stars in corotation resonance with the bar. Unlike previous work, we demonstrate that the retrograde nature of trojan orbits causes the asymmetry in the radial velocity distribution, typical of Hercules in the solar vicinity. We show that trojans remain at capture for only a finite amount of time, before escaping L4 without being captured again. We anticipate that in the kinematic plane the Hercules stream will depopulate along the bar's major axis and be visible at azimuthal angles behind the solar vicinity with a peak toward L4. This test can exclude the outer Lindblad resonance origin of the Hercules stream and be validated by Gaia DR3 and DR4.

As part of the survey component of the Megamaser Cosmology Project, we have discovered a disk megamaser system in the galaxy CGCG 074-064. Using the Green Bank Telescope and the Very Large Array, we have obtained spectral monitoring observations of this maser system at a monthly cadence over the course of two years. We find that the systemic maser features display line-of-sight accelerations of ∼4.4 km s⁻¹ yr⁻¹ that are nearly constant with velocity, while the high-velocity maser features show accelerations that are consistent with zero. We have also used the High-Sensitivity Array to make a high-sensitivity very long baseline interferometric map of the maser system in CGCG 074-064, which reveals that the masers reside in a thin, edge-on disk with a diameter of ∼1.5 mas (0.6 pc). Fitting a three-dimensional warped disk model to the data, we measure a black hole mass of ${2.42}_{-0.20}^{+0.22}\times {10}^{7}\,{M}_{\odot }$ and a geometric distance to the system of ${87.6}_{-7.2}^{+7.9}$ Mpc. Assuming a cosmic microwave background-frame recession velocity of 7308 ± 150 km s⁻¹, we constrain the Hubble constant to ${H}_{0}={81.0}_{-6.9}^{+7.4}$ (stat.) ± 1.4 (sys.) km s⁻¹ Mpc⁻¹.

We have obtained new detailed abundances of the Fe-group elements Sc through Zn (Z = 21–30) in three very metal-poor ([Fe/H] ≈ −3) stars: BD+03^o740, BD−13^o3442, and CD−33^o1173. High-resolution ultraviolet Hubble Space Telescope/Space Telescope Imaging Spectrograph spectra in the wavelength range 2300–3050 Å were gathered, and complemented by an assortment of optical echelle spectra. The analysis featured recent laboratory atomic data for a number of neutral and ionized species for all Fe-group elements except Cu and Zn. A detailed examination of scandium, titanium, and vanadium abundances in large-sample spectroscopic surveys indicates that they are positively correlated in stars with [Fe/H] ≤ −2. The abundances of these elements in BD+03^o740, BD−13^o3442, CD−33^o1173, and HD 84937 (studied in a previous paper of this series) are in accord with these trends and lie at the high end of the correlations. Six elements have detectable neutral and ionized features, and generally their abundances are in reasonable agreement. For Cr we find only minimal abundance disagreement between the neutral (mean of [Cr i/Fe] = +0.01) and ionized species (mean of [Cr ii/Fe] = +0.08), unlike most studies in the past. The prominent exception is Co, for which the neutral species indicates a significant overabundance (mean of [Co i/H] = −2.53), while no such enhancement is seen for the ionized species (mean of [Co ii/H] = −2.93). These new stellar abundances, especially the correlations among Sc, Ti, and V, suggest that models of element production in early high-mass metal-poor stars should be revisited.

An accurate estimate of the interstellar gas density distribution is crucial to understanding the interstellar medium (ISM) and Galactic cosmic rays (CRs). To comprehend the ISM and CRs in a local environment, a study of the diffuse γ-ray emission in a midlatitude region of the third quadrant was performed. The γ-ray data in the 0.1–25.6 GeV energy range of the Fermi Large Area Telescope (LAT) and other interstellar gas tracers such as the HI4PI survey data and the Planck dust thermal emission model were used, and the northern and southern regions were analyzed separately. The variation of the dust emission ${D}_{\mathrm{em}}$ with the total neutral gas column density ${N}_{{\rm{H}}}$ was studied in high dust temperature areas, and the ${N}_{{\rm{H}}}$/${D}_{\mathrm{em}}$ ratio was calibrated using γ-ray data under the assumption of a uniform CR intensity in the studied regions. The measured integrated γ-ray emissivities above 100 MeV are $(1.58\pm 0.04)\times {10}^{-26}\,\mathrm{photons}\,{{\rm{s}}}^{-1}\,{\mathrm{sr}}^{-1}\,{\rm{H}} \mbox{-} {\mathrm{atom}}^{-1}$ and $(1.59\pm 0.02)\times {10}^{-26}\,\mathrm{photons}\,{{\rm{s}}}^{-1}\,{\mathrm{sr}}^{-1}\,{\rm{H}} \mbox{-} {\mathrm{atom}}^{-1}$ in the northern and southern regions, respectively, supporting the existence of a uniform CR intensity in the vicinity of the solar system. While most of the gas can be interpreted to be ${\rm{H}}\,{\rm{I}}$ with a spin temperature of ${T}_{{\rm{S}}}=125\,{\rm{K}}$ or higher, an area dominated by optically thick ${\rm{H}}\,{\rm{I}}$ with ${T}_{{\rm{S}}}\sim 40\,{\rm{K}}$ was identified.

Transits of exoplanets across cool stars contain blended information about structures on the stellar surface and about the planetary body and atmosphere. To advance understanding of how this information is entangled, a surface-flux transport code, based on observed properties of the Sun's magnetic field, is used to simulate the appearance of hypothetical stellar photospheres from the visible near 4000 Å to the near-IR at 1.6 μm by mapping intensities characteristic of faculae and spots onto stellar disks. Stellar appearances are computed for a Sun-like star of solar activity up to a star with a mean magnetic flux density that is ∼30× higher. Simulated transit signals for a Jupiter-class planet are compared with observations. This (1) indicates that the solar paradigm is consistent with transit observations for stars throughout the activity range explored, provided that infrequent large active regions with fluxes up to ∼3 × 10²³ Mx are included in the emergence spectrum, (2) quantitatively confirms that for such a model, faculae brighten relatively inactive stars while starspots dim more-active stars, and suggests (3) that large starspots inferred from transits of active stars are consistent with clusters of more compact spots seen in the model runs, (4) that wavelength-dependent transit-depth effects caused by stellar magnetic activity for the range of activity and the planetary diameter studied here can introduce apparent changes in the inferred exoplanetary radii across wavelengths from a few hundred to a few thousand kilometers, increasing with activity, and (5) that activity-modulated distortions of broadband stellar radiance across the visible to near-IR spectrum can reach several percent.

We discuss absolute calibration strategies for Phase I of the Hydrogen Epoch of Reionization Array (HERA), which aims to measure the cosmological 21 cm signal from the Epoch of Reionization. HERA is a drift-scan array with a 10° wide field of view, meaning bright, well-characterized point-source transits are scarce. This, combined with HERA's redundant sampling of the uv plane and the modest angular resolution of the Phase I instrument, make traditional sky-based and self-calibration techniques difficult to implement with high dynamic range. Nonetheless, in this work, we demonstrate calibration for HERA using point-source catalogs and electromagnetic simulations of its primary beam. We show that unmodeled diffuse flux and instrumental contaminants can corrupt the gain solutions and present a gain-smoothing approach for mitigating their impact on the 21 cm power spectrum. We also demonstrate a hybrid sky and redundant calibration scheme and compare it to pure sky-based calibration, showing only a marginal improvement to the gain solutions at intermediate delay scales. Our work suggests that the HERA Phase I system can be well calibrated for a foreground avoidance power spectrum estimator by applying direction-independent gains with a small set of degrees of freedom across the frequency and time axes.

Precision pulsar timing can be used for a variety of astrophysical tests, from the detection of gravitational waves to probing the properties of the interstellar medium. Here we analyze various noise contributions to pulsar timing residuals from continuous multi-hour observations of seven millisecond pulsars (MSPs). We present scintillation bandwidth measurements for all MSPs in the sample, some for the first time. We also present scintillation timescale measurements and lower limits for all MSPs for the first time. In addition, we present upper limits on the contribution of pulse phase jitter to the timing residual error for all MSPs. These long observations also allow us to constrain variations in dispersion measures (DMs) on hour-long timescales for several millisecond pulsars. We find that there are no apparent DM variations in any of the MSPs studied on these timescales, as expected. In light of new radio telescopes, such as the Canadian Hydrogen Intensity Mapping Experiment, which will be able to time many pulsars for a short time each day, we search for differences in timing precisions from continuous pulse times of arrival (TOAs) and from equivalent length time-discontinuous TOAs. We find no differences in the precision for any of the MSPs in our sample, as expected. We conclude that the TOA variations are consistent with the expected breakdown into template-fitting, jitter, and scintillation errors.

A crucial challenge to successful flare prediction is forecasting periods that transition between "flare-quiet" and "flare-active." Building on earlier studies in this series in which we describe the methodology, details, and results of flare forecasting comparison efforts, we focus here on patterns of forecast outcomes (success and failure) over multiday periods. A novel analysis is developed to evaluate forecasting success in the context of catching the first event of flare-active periods and, conversely, correctly predicting declining flare activity. We demonstrate these evaluation methods graphically and quantitatively as they provide both quick comparative evaluations and options for detailed analysis. For the testing interval 2016–2017, we determine the relative frequency distribution of two-day dichotomous forecast outcomes for three different event histories (i.e., event/event, no-event/event, and event/no-event) and use it to highlight performance differences between forecasting methods. A trend is identified across all forecasting methods that a high/low forecast probability on day 1 remains high/low on day 2, even though flaring activity is transitioning. For M-class and larger flares, we find that explicitly including persistence or prior flare history in computing forecasts helps to improve overall forecast performance. It is also found that using magnetic/modern data leads to improvement in catching the first-event/first-no-event transitions. Finally, 15% of major (i.e., M-class or above) flare days over the testing interval were effectively missed due to a lack of observations from instruments away from the Earth–Sun line.

We studied the final phases of galactic mergers, focusing on interactions between supermassive black holes (SMBHs) and the interstellar medium in a central subkiloparsec region, using an N-body/hydrodynamics code. We observed that the mass accretion rate to one SMBH (10⁷M_⊙) exceeds the Eddington accretion rate when the distance between two black holes (BHs) rapidly decreases. However, this rapid accretion phase does not last for more than 10⁷ yr, and it drops to ∼10% of the Eddington rate in the quasi-steady accretion phase. The second merger event enhances the mass accretion to the BHs; however, this phase takes place on a similar timescale to the first merger event. We also found that the active galactic nucleus (AGN) feedback and the mass accretion to BHs can coexist in the central region of merged galaxies, if the amount of feedback energy is given as $(2\times {10}^{-4}-2\times {10}^{-3})\dot{M}{c}^{2}$, where $\dot{M}$ is the accretion rate to r = 1 pc. The accretion rate is suppressed by ∼1/50 in the quasi-steady accretion phase for $0.02\dot{M}{c}^{2}$. The fraction of the gas that finally falls to each BH is approximately 5%–7% of the supplied total gas mass (10⁸M_⊙), and 15%–20% of the gas forms a circumnuclear gas inside 100 pc. This remnant gas heavily obscures the luminous phase of the AGNs during merger events, and the moderate AGN feedback does not alter this property.

We have conducted a survey of candidate hot subdwarf (HSD) stars in the southern sky searching for fast transits, eclipses, and sinusoidal-like variability in the Evryscope light curves. The survey aims to detect transit signals from Neptune-size planets to gas giants, and eclipses from M-dwarfs and brown dwarfs. The other variability signals are primarily expected to be from compact binaries and reflection effect binaries. Due to the small size of HSDs (R ≈ 0.2 R_⊙), transit and eclipse signals are expected to last only ≈20 minutes, but with large signal depths (up to completely eclipsing if the orientation is edge on). With its 2 minute cadence and continuous observation, the Evryscope is well placed to recover these fast transits and eclipses. The very large field of view (8150 deg²) is critical to obtain enough HSD targets, despite their rarity. We identified ≈11,000 potential HSDs from the 9.3 M Evryscope light curves for sources brighter than m_g = 15. With our machine-learning spectral classifier, we flagged high confidence targets and estimate the total HSDs in the survey to be ≈1400. The light-curve search detected three planet transit candidates, shown to have stellar companions from follow-up analysis. We discovered several new compact binaries (including two with unseen degenerate companions), two eclipsing binaries with M-dwarf companions, as well as new reflection effect binaries and others with sinusoidal-like variability. Four of the discoveries are being published in separate follow-up papers, and we discuss the follow-up potential of the other discoveries.

The core-collapse supernova (CCSN) mechanism is fundamentally 3D, with instabilities, convection, and turbulence playing crucial roles in aiding neutrino-driven explosions. Simulations of CCNSe including accurate treatments of neutrino transport and sufficient resolution to capture key instabilities remain among the most expensive numerical simulations in astrophysics, prohibiting large parameter studies in 2D and 3D. Studies spanning a large swath of the incredibly varied initial conditions of CCSNe are possible in 1D, though such simulations must be artificially driven to explode. We present a new method for including the most important effects of convection and turbulence in 1D simulations of neutrino-driven CCSNe, called Supernova Turbulence In Reduced-dimensionality, or STIR. Our new approach includes crucial terms resulting from the turbulent and convective motions of the flow. We estimate the strength of convection and turbulence using a modified mixing-length theory approach, introducing a few free parameters to the model that are fit to the results of 3D simulations. For sufficiently large values of the mixing-length parameter, turbulence-aided neutrino-driven explosions are obtained. We compare the results of STIR to high-fidelity 3D simulations and perform a parameter study of CCSN explosion using 200 solar-metallicity progenitor models from 9 to 120 ${M}_{\odot }$. We find that STIR is a better predictor of which models will explode in multidimensional simulations than other methods of driving explosions in 1D. We also present a preliminary investigation of predicted observable characteristics of the CCSN population from STIR, such as the distributions of explosion energies and remnant masses.

The Next Generation Virgo Cluster Survey (NGVS) was designed to provide a deep census of baryonic structures in the Virgo cluster. The survey covers the 104 deg² area from the core of Virgo out to one virial radius, in the u*griz bandpasses, to a point-source depth of g ∼ 25.9 mag (10σ) and a single pixel surface brightness limit of μ_g ∼ 29 mag arcsec⁻² (2σ above the sky). Here we present the final catalog of 404 Virgo galaxies located within a 3.71 deg² (0.3 Mpc²) region centered on M87, Virgo's dominant galaxy. Of these, 154 were previously uncataloged and span the range 17.8 mag < g < 23.7 mag (−13.4 mag < M_g < −7.4 mag at the 16.5 Mpc distance of Virgo). Extensive simulations show that the NGVS catalog is complete down to g = 18.6 mag (M_g = −12.5 mag, corresponding to a stellar mass ${ \mathcal M }\sim 1.6\times {10}^{7}{{ \mathcal M }}_{\odot }$ for an old stellar population), and 50% complete at g = 22.0 mag (M_g = −9.1 mag, ${ \mathcal M }\sim 6.2\times {10}^{5}{{ \mathcal M }}_{\odot }$). The NGVS 50% completeness limit is 3 mag deeper than that of the Virgo Cluster Catalog (VCC), which has served as Virgo's reference standard for over a quarter century, and 2 mag deeper than the VCC detection limit. We discuss the procedure adopted for the identification of objects and the criteria used to assess cluster membership. For each of the 404 galaxies in the NGVS Virgo Cluster core catalog, we present photometric and structural parameters based on a nonparametric curve-of-growth and isophotal analysis, as well as parametric (Sérsic, double-Sérsic, and/or core-Sérsic) fits to the one-dimensional surface brightness profiles and two-dimensional light distributions.

We report Atacama Large Millimeter/submillimeter Array and Very Large Array continuum observations that potentially identify the four youngest protostars in the Orion Molecular Clouds taken as part of the Orion VANDAM program. These are distinguished by bright, extended, irregular emission at 0.87 and 8 mm and are optically thick at 0.87 mm. These structures are distinct from the disk or point-like morphologies seen toward the other Orion protostars. The 0.87 mm emission implies temperatures of 41–170 K, requiring internal heating. The bright 8 mm emission implies masses of 0.5–1.2 M_⊙ assuming standard dust opacity models. One source has a Class 0 companion, while another exhibits substructure indicating a companion candidate. Three compact outflows are detected, two of which may be driven by companions, with dynamical times of ∼300 to ∼1400 yr. The slowest outflow may be driven by a first hydrostatic core. These protostars appear to trace an early phase when the centers of collapsing fragments become optically thick to their own radiation and compression raises the gas temperature. This phase is thought to accompany the formation of hydrostatic cores. A key question is whether these structures are evolving on freefall times of ∼100 yr, or whether they are evolving on Kelvin–Helmholtz times of several thousand years. The number of these sources imply a lifetime of ∼6000 yr, in closer agreement with the Kelvin–Helmholtz time. In this case, rotational and/or magnetic support could be slowing the collapse.

We have conducted a survey of 328 protostars in the Orion molecular clouds with the Atacama Large Millimeter/submillimeter Array at 0.87 mm at a resolution of ∼01 (40 au), including observations with the Very Large Array at 9 mm toward 148 protostars at a resolution of ∼008 (32 au). This is the largest multiwavelength survey of protostars at this resolution by an order of magnitude. We use the dust continuum emission at 0.87 and 9 mm to measure the dust disk radii and masses toward the Class 0, Class I, and flat-spectrum protostars, characterizing the evolution of these disk properties in the protostellar phase. The mean dust disk radii for the Class 0, Class I, and flat-spectrum protostars are ${44.9}_{-3.4}^{+5.8}$, ${37.0}_{-3.0}^{+4.9}$, and ${28.5}_{-2.3}^{+3.7}$ au, respectively, and the mean protostellar dust disk masses are 25.9${}_{-4.0}^{+7.7}$, ${14.9}_{-2.2}^{+3.8}$, ${11.6}_{-1.9}^{+3.5}$${M}_{\oplus }$, respectively. The decrease in dust disk masses is expected from disk evolution and accretion, but the decrease in disk radii may point to the initial conditions of star formation not leading to the systematic growth of disk radii or that radial drift is keeping the dust disk sizes small. At least 146 protostellar disks (35% of 379 detected 0.87 mm continuum sources plus 42 nondetections) have disk radii greater than 50 au in our sample. These properties are not found to vary significantly between different regions within Orion. The protostellar dust disk mass distributions are systematically larger than those of Class II disks by a factor of >4, providing evidence that the cores of giant planets may need to at least begin their formation during the protostellar phase.

On 2019 August 14, the Advanced LIGO and Virgo interferometers detected the high-significance gravitational wave (GW) signal S190814bv. The GW data indicated that the event resulted from a neutron star–black hole (NSBH) merger, or potentially a low-mass binary BH merger. Due to the low false-alarm rate and the precise localization (23 deg² at 90%), S190814bv presented the community with the best opportunity yet to directly observe an optical/near-infrared counterpart to an NSBH merger. To search for potential counterparts, the GROWTH Collaboration performed real-time image subtraction on six nights of public Dark Energy Camera images acquired in the 3 weeks following the merger, covering >98% of the localization probability. Using a worldwide network of follow-up facilities, we systematically undertook spectroscopy and imaging of optical counterpart candidates. Combining these data with a photometric redshift catalog, we ruled out each candidate as the counterpart to S190814bv and placed deep, uniform limits on the optical emission associated with S190814bv. For the nearest consistent GW distance, radiative transfer simulations of NSBH mergers constrain the ejecta mass of S190814bv to be M_ej < 0.04 M_⊙ at polar viewing angles, or M_ej < 0.03 M_⊙ if the opacity is κ < 2 cm²g⁻¹. Assuming a tidal deformability for the NS at the high end of the range compatible with GW170817 results, our limits would constrain the BH spin component aligned with the orbital momentum to be χ < 0.7 for mass ratios Q < 6, with weaker constraints for more compact NSs.

We probed the magnetic fields in high-redshift galaxies using excess extragalactic contribution to residual rotation measure (RRM) for quasar sightlines with intervening Mg ii absorbers. Based on a large sample of 1132 quasars, we have computed RRM distributions broadening using median absolute deviation from the mean (${\sigma }_{\mathrm{rrm}}^{\mathrm{md}}$), and found it to be 17.1 ± 0.7 rad m⁻² for 352 sightlines having Mg ii intervening absorbers in comparison to its value of 15.1 ± 0.6 rad m⁻² for 780 sightlines without such absorbers, resulting in an excess broadening (${\sigma }_{\mathrm{rrm}}^{\mathrm{ex}}$) of 8.0 ± 1.9 rad m⁻² among these two subsamples. This value of ${\sigma }_{\mathrm{rrm}}^{\mathrm{ex}}$, has allowed us to constrain the average strength of magnetic field (rest frame) in high-redshift galaxies responsible for these Mg ii absorbers, to be ∼1.3 ± 0.3 μG at a median redshift of 0.92. This estimate of magnetic field is consistent with the reported estimate in earlier studies based on radio-infrared correlation and energy equipartition for galaxies in the local universe. A similar analysis on subsample split based on the radio spectral index, α (with F_ν ∝ ν^α), for flat (α ≥ −0.3; 315 sources) and steep (α ≤ −0.7; 476 sources) spectrum sources shows a significant ${\sigma }_{\mathrm{rrm}}^{\mathrm{ex}}$ (at 3.5σ level) for the former and absent in the latter. An anticorrelation found between the ${\sigma }_{\mathrm{rrm}}^{\mathrm{md}}$ and percentage polarization (p) with a similar Pearson correlation of −0.62 and −0.87 for subsamples with and without Mg ii, respectively, suggests the main contribution for decrements in the p value to be intrinsic to the local environment of quasars.

We present spectroscopic determinations of the effective temperatures, surface gravities, and metallicities for 21 M dwarfs observed at high resolution (R ∼ 22,500) in the H band as part of the Sloan Digital Sky Survey (SDSS)-IV Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey. The atmospheric parameters and metallicities are derived from spectral syntheses with 1D LTE plane-parallel MARCS models and the APOGEE atomic/molecular line list, together with up-to-date H₂O and FeH molecular line lists. Our sample range in T_eff from ∼3200 to 3800 K, where 11 stars are in binary systems with a warmer (FGK) primary, while the other 10 M dwarfs have interferometric radii in the literature. We define an ${M}_{{K}_{S}}$–radius calibration based on our M-dwarf radii derived from the detailed analysis of APOGEE spectra and Gaia DR2 distances, as well as a mass–radius relation using the spectroscopically derived surface gravities. A comparison of the derived radii with interferometric values from the literature finds that the spectroscopic radii are slightly offset toward smaller values, with Δ = −0.01 ± 0.02 R⋆/R_⊙. In addition, the derived M-dwarf masses based upon the radii and surface gravities tend to be slightly smaller (by ∼5%–10%) than masses derived for M-dwarf members of eclipsing binary systems for a given stellar radius. The metallicities derived for the 11 M dwarfs in binary systems, compared to metallicities obtained for their hotter FGK main-sequence primary stars from the literature, show excellent agreement, with a mean difference of [Fe/H](M dwarf – FGK primary) = +0.04 ± 0.18 dex, confirming the APOGEE metallicity scale derived here for M dwarfs.

This article explores the sizes of sunspots as determined by naked-eye sunspot observations (NSOs). The international sunspot number (ISN), the group sunspot number, and the Greenwich photo-heliographic results (GPR) were utilized. According to the ISN results, 64% of NSOs from 1819 to 1918 have been identified as large sunspots. We found that the sunspot sizes had been considerably underestimated using the ISN data (compared to using the GPR data). About 40% of NSOs from 1819 to 1918 have been identified as giant sunspots, which have ranks of sunspot areas smaller than 5%. The results in this article indicate that the majority of NSOs are large sunspots. This calls into question the previous understanding that NSOs include sunspots of all sizes above the visibility limit.

We discuss a technique for detecting and locating rapid transient electromagnetic counterparts to gravitational wave sources that affords a reprieve of several hours after the gravitational wave event. The technique relies on detecting a scattering halo produced if X-rays emitted at the gravitational wave event scatter off Galactic dust clouds. The travel-time delay of these scattered photons makes them detectable up to several hours after the prompt event; the location of the gravitational wave source will be at the geometric center of the halo, which can be determined with precision sufficient to allow the host galaxy to be identified.

We report the discovery of two ultra-faint stellar systems found in early data from the DECam Local Volume Exploration survey (DELVE). The first system, Centaurus I (DELVE J1238–4054), is identified as a resolved overdensity of old and metal-poor stars with a heliocentric distance of ${\text{}}{D}_{\odot }={116.3}_{-0.6}^{+0.6}\,\mathrm{kpc}$, a half-light radius of ${r}_{h}={2.3}_{-0.3}^{+0.4}\,\mathrm{arcmin}$, an age of $\tau \gt 12.85\,\mathrm{Gyr}$, a metallicity of $Z={0.0002}_{-0.0002}^{+0.0001}$, and an absolute magnitude of ${M}_{V}=-{5.55}_{-0.11}^{+0.11}\,\mathrm{mag}$. This characterization is consistent with the population of ultra-faint satellites and confirmation of this system would make Centaurus I one of the brightest recently discovered ultra-faint dwarf galaxies. Centaurus I is detected in Gaia DR2 with a clear and distinct proper motion signal, confirming that it is a real association of stars distinct from the Milky Way foreground; this is further supported by the clustering of blue horizontal branch stars near the centroid of the system. The second system, DELVE 1 (DELVE J1630–0058), is identified as a resolved overdensity of stars with a heliocentric distance of ${\text{}}{D}_{\odot }={19.0}_{-0.6}^{+0.5}\,\mathrm{kpc}$, a half-light radius of ${r}_{h}={0.97}_{-0.17}^{+0.24}\,\mathrm{arcmin}$, an age of $\tau ={12.5}_{-0.7}^{+1.0}\,\mathrm{Gyr}$, a metallicity of $Z={0.0005}_{-0.0001}^{+0.0002}$, and an absolute magnitude of ${M}_{V}=-{0.2}_{-0.6}^{+0.8}\,\mathrm{mag}$, consistent with the known population of faint halo star clusters. Given the low number of probable member stars at magnitudes accessible with Gaia DR2, a proper motion signal for DELVE 1 is only marginally detected. We compare the spatial position and proper motion of both Centaurus I and DELVE 1 with simulations of the accreted satellite population of the Large Magellanic Cloud (LMC) and find that neither is likely to be associated with the LMC.

We combine the NLTE spectral analysis of the detached O-type eclipsing binary OGLE-LMC-ECL-06782 with the analysis of the radial velocity curve and light curve to measure an independent distance to the Large Magellanic Cloud (LMC). In our spectral analysis we study composite spectra of the system at quadrature and use the information from radial velocity and light curve about stellar gravities, radii, and component flux ratio to derive effective temperature, reddening, extinction, and intrinsic surface brightness. We obtain a distance modulus to the LMC of m − M = 18.53 ± 0.04 mag. This value is 0.05 mag larger than the precision distance obtained recently from the analysis of a large sample of detached, long period late spectral type eclipsing binaries but agrees within the margin of the uncertainties. We also determine the surface brightnesses of the system components and find good agreement with the published surface brightness–color relationship. A comparison of the observed stellar parameters with the prediction of stellar evolution based on the MESA stellar evolution code shows reasonable agreement, but requires a reduction of the internal angular momentum transport to match the observed rotational velocities.

In quiet regions on the solar surface, turbulent convective motions of granulation play an important role in creating small-scale magnetic structures, as well as in energy injection into the upper atmosphere. The turbulent nature of granulation can be studied using spectral line profiles, especially line broadening, which contain information on the flow field smaller than the spatial resolution of an instrument. Moreover, the Doppler velocity gradient along a line of sight (LOS) causes line broadening as well. However, the quantitative relationship between velocity gradient and line broadening has not been understood well. In this study, we perform bisector analyses using the spectral profiles obtained using the spectropolarimeter of the Hinode/Solar Optical Telescope to investigate the relationship of line broadening and bisector velocities with the granulation flows. The results indicate that line broadening has a positive correlation with the Doppler velocity gradients along the LOS. We found excessive line broadening in fading granules, that cannot be explained only by the LOS velocity gradient, although the velocity gradient is enhanced in the process of fading. If this excessive line broadening is attributed to small-scale turbulent motions, the averaged turbulent velocity is obtained as 0.9 km s⁻¹.

We investigate gross properties of binary components and remnant in GW170817 using equations of state (EoSs) within the finite temperature field theoretical models. We also adopt finite temperature EoSs in the density-dependent hadron field theory for this study. Properties of binary components are studied using zero temperature EoSs. Particularly, we investigate tidal deformabilities and radii of binary components in light of GW170817. An analytical expression relating the radii and the combined tidal deformability is obtained for binary neutron star masses in the range 1.1 M_⊙ ≲ M ≲ 1.6 M_⊙. The upper bound on the tidal deformability gives the upper bound on the neutron star radius as 13 km. Next, the role of finite temperature on the remnant in GW170817 is explored. In this case, we investigate the gravitational and baryon mass, radius, Kepler frequency, and moment of inertia of the rigidly rotating remnant for different EoSs at fixed entropy per baryon. The remnant radius is enlarged due to thermal effects compared with the zero temperature case. Consequently, it is found that the Kepler frequency is much lower at higher entropy per baryon than that of the case at zero temperature. These findings are consistent with the results found in the literature.

We present analytical reconstructions of SN Ia delay time distributions (DTDs) by way of two independent methods: by a Markov Chain Monte Carlo best-fit technique comparing the volumetric SN Ia rate history to today's compendium cosmic star formation history, and second through a maximum likelihood analysis of the star formation rate histories of individual galaxies in the GOODS/CANDELS field, in comparison to their resultant SN Ia yields. We adopt a flexible skew-normal DTD model, which could match a wide range of physically motivated DTD forms. We find a family of solutions that are essentially exponential DTDs, similar in shape to the β ≈ −1 power-law DTDs, but with more delayed events (>1 Gyr in age) than prompt events (<1 Gyr). Comparing these solutions to delay time measures separately derived from field galaxies and galaxy clusters, we find the skew-normal solutions can accommodate both without requiring a different DTD form in different environments. These model fits are generally inconsistent with results from single-degenerate binary population synthesis models, and are seemingly supportive of double-degenerate progenitors for most SN Ia events.

Gas convection is observed in the solar photosphere as granulation, i.e., having highly time-dependent cellular patterns, consisting of numerous bright cells called granules and dark surrounding channels called intergranular lanes. Many efforts have been made to characterize the granulation, which may be used as an energy source for various types of dynamical phenomena. Although the horizontal gas flow dynamics in intergranular lanes may play a vital role, they are poorly understood. This is because the Doppler signals can be obtained only at the solar limb, where the signals are severely degraded by a foreshortening effect. To reduce such a degradation, we use Hinode's spectroscopic data, which are free from a seeing-induced image degradation, and improve the image quality by correcting for stray light in the instruments. The data set continuously covers from the solar disk to the limb, providing a multidirectional line-of-sight (LOS) diagnosis against the granulation. The obtained LOS flow-field variation across the disk indicates a horizontal flow speed of 1.8–2.4 km s⁻¹. We also derive the spatial distribution of the horizontal flow speed, which is 1.6 km s⁻¹ in granules and 1.8 km s⁻¹ in intergranular lanes, and where the maximum speed is inside intergranular lanes. This result newly suggests the following sequence of horizontal flow: a hot rising gas parcel is strongly accelerated from the granular center, even beyond the transition from the granules to the intergranular lanes, resulting in the fastest speed inside the intergranular lanes, and the gas may also experience decelerations in the intergranular lane.

H₂CO is one of the most abundant organic molecules in protoplanetary disks and can serve as a precursor to more complex organic chemistry. We present an Atacama Large Millimeter/submillimeter Array survey of H₂CO toward 15 disks covering a range of stellar spectral types, stellar ages, and dust continuum morphologies. H₂CO is detected toward 13 disks and tentatively detected toward a fourteenth. We find both centrally peaked and centrally depressed emission morphologies, and half of the disks show ring-like structures at or beyond expected CO snowline locations. Together these morphologies suggest that H₂CO in disks is commonly produced through both gas-phase and CO-ice-regulated grain-surface chemistry. We extract disk-averaged and azimuthally-averaged H₂CO excitation temperatures and column densities for four disks with multiple H₂CO line detections. The temperatures are between 20–50 K, with the exception of colder temperatures in the DM Tau disk. These temperatures suggest that H₂CO emission in disks generally emerges from the warm molecular layer, with some contributions from the colder midplane. Applying the same H₂CO excitation temperatures to all disks in the survey, we find that H₂CO column densities span almost three orders of magnitude (∼5 × 10¹¹–5 × 10¹⁴ cm⁻²). The column densities appear uncorrelated with disk size and stellar age, but Herbig Ae disks may have less H₂CO compared to T Tauri disks, possibly because of less CO freeze-out. More H₂CO observations toward Herbig Ae disks are needed to confirm this tentative trend, and to better constrain under which disk conditions H₂CO and other oxygen-bearing organics efficiently form during planet formation.

The timing properties of the millisecond pulsar PSR J1939+2134—very high rotation frequency, very low time derivative of rotation frequency, no timing glitches, and relatively low timing noise—are responsible for its exceptional timing stability over decades. It has been timed by various groups since its discovery, at diverse radio frequencies, using different hardware and analysis methods. Most of the timing data is now available in the public domain in two segments, which have not been combined so far. This work analyzes the combined data by deriving uniform methods of data selection, derivation of Dispersion Measure (DM), accounting for correlation due to "red" noise, etc. The timing noise of this pulsar is very close to a sinusoid, with a period of approximately 31 yr. The main results of this work are: (1) the clock of PSR J1939+2134 is stable at the level of almost one part in 10¹⁵ over about 31 yr; (2) the power-law index of the spectrum of electron density fluctuations in the direction of PSR J1939+2134 is 3.86 ± 0.04; (3) a Moon-sized planetary companion, in an orbit of semimajor axis about 11 astronomical units and eccentricity ≈0.2, can explain the timing noise of PSR J1939+2134; (4) precession under electromagnetic torque with very small values of oblateness and wobble angle can also be the explanation but with reduced confidence; and (5) there is an excess timing noise of about 8 μs amplitude during the epochs of steepest DM gradient, of unknown cause.

Evidence has accumulated suggesting the clustering of radio loud quasars (RLQs) is greater than for radio quiet quasars. We interpret these results in a context in which the fraction of RLQ formation is f_RLQ ≤ f_RQQ compared to that for radio quiet quasars for all environments and redshifts. Because we assume that post-merger cold gas onto large black holes produces either a radio loud or a radio quiet quasar, we show that for the largest black hole masses that live in the largest dark matter halos, f_RLQ approaches 0.5 from below but does not exceed it, such that in rich clusters the formation of an RLQ tends to be equally likely to occur as a radio quiet quasar. In dark matter halos with smaller mass, by contrast, radio quiet quasars are more likely to form and the likelihood increases inversely with dark matter halo mass. As a result, averaging over a population of radio loud and radio quiet quasars will necessarily generate lower average black hole masses for the radio quiet subgroup. Hence, despite the fact that the formation of radio quiet quasars is preferred over RLQs in any environment, at any mass scale, at any luminosity, or redshift, averaging over a range of RLQs will give the appearance that they are preferred in cluster environments over radio quiet quasars. We show how this also accounts for the order of magnitude difference in the total number of jetted active galaxies compared to nonjetted counterparts.

The lenticular galaxy IC 676 is a barred galaxy with double nuclei and active star formation in the central region. In this work we present the long-slit spectroscopy and archival multiwavelength images to investigate the nature and origin of the double nuclei in IC 676. Through photometric 1D brightness profiles and 2D image decomposition, we show that this galaxy consists of a stellar bar with the length of ∼2.5 kpc and two Sérsic disks both of which with Sérsic index n ∼ 1.3. There is probably little or no bulge component assembled in IC 676. The luminosities of the double nuclei are primarily dominated by young stellar populations within the ages of 1–10 Myr. The northern nucleus has stronger star formation activity than the southern one. The surface densities of the star formation rate in the double nuclei are similar to those in starburst galaxies or the circumnuclear star-forming regions in spiral galaxies. Each of the double nuclei in IC 676 likely consists of young massive star clusters, which can be resolved as bright knots in the Hubble Space Telescope high-resolution image. Our results suggest that IC 676 likely has a complex formation and evolutionary history. The secular processes driven by the stellar bar and external accretion may dominate the formation and evolution of its double nuclei. This indicates that the secular evolution involving the internal and external drivers may have an important contribution for the evolution of lenticular galaxies.

Secular extragalactic parallax caused by the solar system's velocity relative to the cosmic microwave background rest frame may be observable as a dipole proper motion field with amplitude 78 μas yr⁻¹ Mpc. Nearby galaxies also exhibit proper motions caused by their transverse peculiar velocities that prevent detection of secular parallax for any single galaxy, although a statistical detection may be made instead. Such a detection could constrain the local Hubble parameter. We present methods to measure secular parallax using correlated extragalactic proper motions and find a first limit on the secular parallax amplitude using proper motions of 232 nearby galaxies from Gaia Data Release 2. The recovered dipole has an insignificant upper limit of 3500 μas yr⁻¹ Mpc. This measurement will be improved by a larger sample size and reduced proper motion uncertainties in future data releases. Using the local peculiar velocity field derived from Cosmicflows-3, we simulate galaxy proper motions and predict that a significant detection (5–10σ) of the secular parallax amplitude will be possible by Gaia's end of mission. The detection does not correspond to a constraint on the Hubble parameter because it depends on nearby (<5 Mpc), bright (G < 15 mag) galaxies and the underlying peculiar motion dipole. We further investigate the implications of our simulations for the study of transverse peculiar velocities. The peculiar velocity field additionally results in low multipole-correlated proper motions on the order of 0.3 μas yr⁻¹ that may be confounded with other cosmological proper motion measurements, such as limits on the gravitational-wave background and the anisotropy of the Hubble expansion.

There are indications that the perpendicular transport of energetic particles is sometimes subdiffusive for intermediate timescales. This corresponds to a scenario where particles follow diffusive magnetic field lines while they also move diffusively in the parallel direction. This type of transport should occur at times after the ballistic regime but before the particles experience the transverse complexity of the turbulence. In this article we present a detailed analytical investigation of distribution functions of particles experiencing compound subdiffusion. Simple approximations of particle distributions are derived which can easily be used in applications. We also compare our findings with test-particle simulations performed for slab turbulence corresponding to the case of vanishing transverse turbulence structure.

We present a weak-lensing analysis of X-ray galaxy groups and clusters selected from the XMM-XXL survey using the first-year data from the Hyper Suprime-Cam (HSC) Subaru Strategic Program. Our joint weak-lensing and X-ray analysis focuses on 136 spectroscopically confirmed X-ray-selected systems at 0.031 ≤ z ≤ 1.033 detected in the 25 deg² XXL-N region, which largely overlaps with the HSC-XMM field. With high-quality HSC weak-lensing data, we characterize the mass distributions of individual clusters and establish the concentration–mass (c–M) relation for the XXL sample, by accounting for selection bias and statistical effects and marginalizing over the remaining mass calibration uncertainty. We find the mass-trend parameter of the c–M relation to be $\beta =-0.07\pm 0.28$ and the normalization to be ${c}_{200}=4.8\pm 1.0\,(\mathrm{stat})\pm 0.8\,(\mathrm{syst})$ at ${M}_{200}={10}^{14}\,{h}^{-1}\,{M}_{\odot }$ and z = 0.3. We find no statistical evidence for redshift evolution. Our weak-lensing results are in excellent agreement with dark-matter-only c–M relations calibrated for recent ΛCDM cosmologies. The level of intrinsic scatter in c₂₀₀ is constrained as $\sigma (\mathrm{ln}{c}_{200})\lt 24 \%$ ($99.7 \%$ CL), which is smaller than predicted for the full population of ΛCDM halos. This is likely caused in part by the X-ray selection bias in terms of the cool-core or relaxation state. We determine the temperature–mass (T_X–M₅₀₀) relation for a subset of 105 XXL clusters that have both measured HSC lensing masses and X-ray temperatures. The resulting T_X–M₅₀₀ relation is consistent with the self-similar prediction. Our T_X–M₅₀₀ relation agrees with the XXL DR1 results at group scales but has a slightly steeper mass trend, implying a smaller mass scale in the cluster regime. The overall offset in the T_X–M₅₀₀ relation is at the ∼1.5σ level, corresponding to a mean mass offset of $34 \% \pm 20 \%$. We also provide bias-corrected, weak-lensing-calibrated M₂₀₀ and M₅₀₀ mass estimates of individual XXL clusters based on their measured X-ray temperatures.

We present the highest-resolution—15 pc (003)—ALMA ¹²CO(2–1) line emission and 1.3 mm continuum maps, tracers of the molecular gas and dust, respectively, in the nearby merging galaxy system NGC 6240, which hosts two supermassive black holes growing simultaneously. These observations provide an excellent spatial match to existing HubbleSpace Telescope (HST) optical and near-infrared observations of this system. A significant molecular gas mass, ∼9 × 10⁹M_⊙, is located between the two nuclei, forming a clumpy stream kinematically dominated by turbulence, rather than a smooth rotating disk, as previously assumed from lower-resolution data. Evidence for rotation is seen in the gas surrounding the southern nucleus but not in the northern one. Dynamical shells can be seen, likely associated with nuclear supernova remnants. We further detect the presence of significant high-velocity outflows, some of them reaching velocities >500 km s⁻¹, affecting a significant fraction, ∼11%, of the molecular gas in the nuclear region. Inside the spheres of influence of the northern and southern supermassive black holes, we find molecular masses of 7.4 × 10⁸ and 3.3 × 10⁹M_⊙, respectively. We are thus directly imaging the reservoir of gas that can accrete onto each supermassive black hole. These new ALMA maps highlight the critical need for high-resolution observations of molecular gas in order to understand the feeding of supermassive black holes and its connection to galaxy evolution in the context of a major galaxy merger.

The high-energy emission from nearby, star-forming galaxies is dominated by X-ray binaries, where a neutron star or black hole is accreting mass from either a low-mass (≲3 M_⊙) or high-mass (≳8 M_⊙) star. Donor stars with intermediate masses ≈3–7 M_⊙ are also possible, but rarer in our Galaxy. Since it is not possible to separate low-, intermediate-, and high-mass X-ray binaries (LMXBs, IMXBs, and HMXBs) from their X-ray properties alone, we use optical images of M101 taken with the Hubble Space Telescope to directly constrain the masses of donor stars in X-ray binaries down to ≈3 M_⊙. For X-ray binaries that still live within their parent star cluster, the age of the cluster provides strong constraints on the mass of the donor and hence type of binary. We present the classification, on a source-by-source basis, of 140 X-ray point sources in the nearby spiral galaxy M101 (D = 6.4 ± 0.2 Mpc). We find that, overall, HMXBs appear to follow the spiral arms, while LMXBs dominate the bulge region as expected, but also appear to form an inter-arm disk population. The X-ray luminosity functions for HMXBs and LMXBs are well fit by a power-law distribution, dN/dL_X ∝ L^α, with α = −1.71 ± 0.06 (HMXBs) and α = −1.96 ± 0.08 (LMXBs), and the brightest sources are consistent with the expectations from sampling statistics without requiring a physical cutoff. Overall, our results for HMXB and LMXB populations agree well with the specific star formation rate map presented for M101 recently by Lehmer and collaborators.

The recently discovered 100X weaker quiescent (Q) mode in pulsar B0823+26 is X-ray quiet, unlike its usual bright (B) mode. Arecibo polarimetric observations were conducted to confirm the pulsar's orthogonal geometry and investigate the emission associated with its main pulse (MP), interpulse (IP), and postcursor (PC) components. Main results: (1) the pulsar's MP, PC, and IP are present in both modes and exhibit a two-pole orthogonal geometry. (2) The B-mode MP is dominated by core emission with weak conal outriders, whereas, the Q-mode double profile shows mainly residual conal emission with little core. The IP is conal in both modes. (3) Sporadic intrapulse emission trailing the PC is detected in the Q mode. (4) B0823+26 falls close to an $\dot{E}$ boundary of 10^32.5 erg s⁻¹ (or B₁₂/P² ∼ 2.5) between core- and conal-dominated profiles—which also represents a boundary between pair-plasma source configurations above the polar cap. For larger energies, the pair-formation front is central, flat, and generates backflow heating, whereas for smaller energies it is peripheral, lower, and produces little heating. (5) Apparently, the pulsar is able to assume both core- and conal-dominated "states" corresponding to its bright and weak modes. These circumstances appear to explain B0823+26's B-mode X-ray bright/core-dominated radio emission or Q-mode X-ray faint/conal radio emission—and why the IP is X-ray quiet in both modes. (6) These same considerations applied to B0943+10 may explain why its brighter radio mode was conal and X-ray quiet, while the weaker one was X-ray bright—because its peripheral sightline would miss most core radiation.

We measure the 10 and 18 μm silicate features in a sample of 67 local (z < 0.1) type 1 active galactic nuclei (AGN) with available Spitzer spectra dominated by nonstellar processes. We find that the 10 μm silicate feature peaks at ${10.3}_{-0.9}^{+0.7}\,\mu {\rm{m}}$ with a strength (Si_p = ln f_p(spectrum)/f_p(continuum)) of ${0.11}_{-0.36}^{+0.15}$, while the 18 μm one peaks at ${17.3}_{-0.7}^{+0.4}\,\mu {\rm{m}}$ with a strength of ${0.14}_{-0.06}^{+0.06}$. We select from this sample sources with the strongest 10 μm silicate strength (${\sigma }_{{\mathrm{Si}}_{10\mu {\rm{m}}}}\gt 0.28$, 10 objects). We carry out a detailed modeling of the infrared spectrometer/Spitzer spectra by comparing several models that assume different geometries and dust composition: a smooth torus model, two clumpy torus models, a two-phase medium torus model, and a disk+outflow clumpy model. We find that the silicate features are well modeled by the clumpy model of Nenkova et al., and among all models, those including outflows and complex dust composition are the best. We note that even in AGN-dominated galaxies, it is usually necessary to add stellar contributions to reproduce the emission at the shortest wavelengths.

The Zeeman effect has been the only method to directly probe the magnetic field strength in molecular clouds. The Bayesian analysis of Zeeman measurements carried out by Crutcher et al. is the only reference for cloud magnetic field strength. Here we extended their model and Bayesian analysis of the relation between field strength (B) and volume density (n) in the following three directions based on the recent observational and theoretical development. First, we take R, the observational uncertainty of n, as a parameter to be estimated from data. Second, the restriction of α, the index of the B–n relationship, is relieved from [0, 0.75] to [0, 1]. Third, we allow f, the minimum-to-maximum B ratio, to vary with n. Our results show that taking R as a parameter provides a better fitting to the B–n relationship and much more reliable estimates on R, f, and the changing point of α. Arguably our most important finding is that α cannot be reliably estimated by any of the models studied here, either from us or Crutcher et al., if R > 2, which is indeed the case from our estimate. This is the so-called errors-in-variables bias, a well known problem for statisticians.

The composition of a protoplanetary disk is set by a combination of interstellar inheritance and gas and grain surface chemical reactions within the disk. The survival of inherited molecules, as well as the disk in situ chemistry depends on the local temperature, density and irradiation environment, which can change over time due to stellar and disk evolution, as well as transport in the disk. We address one aspect of this coupling between the physical and chemical evolution in disks by following accretion streamlines of gas and small grains in the disk midplane, while simultaneously taking the evolving star into account. This approach is computationally efficient and enables us to take into account changing physical conditions without reducing the chemical network. We find that many species are enhanced in the inner disk midplane in the dynamic model due to inward transport of cosmic-ray driven chemical products, resulting in, e.g., orders of magnitude hydrocarbon enhancements at 1 au, compared to a static disk. For several other chemical families, there is no difference between the static and dynamic models, indicative of a robust chemical reset, while yet others show differences between static and dynamic models that depend on complex interactions between physics and chemistry during the inward track. The importance of coupling dynamics and chemistry when modeling the chemical evolution of protoplanetary disks thus depends on what chemistry is of interest.

One-zone models constructed to match observed stellar abundance patterns have been used extensively to constrain the sites of nucleosynthesis with sophisticated libraries of stellar evolution and stellar yields. The metal mixing included in these models is usually highly simplified, although it is likely to be a significant driver of abundance evolution. In this work we use high-resolution hydrodynamics simulations to investigate how metals from individual enrichment events with varying source energies E_ej mix throughout the multiphase interstellar medium (ISM) of a low-mass (M_gas = 2 × 10⁶M_⊙), low-metallicity, isolated dwarf galaxy. These events correspond to the characteristic energies of both common and exotic astrophysical sites of nucleosynthesis, including asymptotic giant branch winds (E_ej ∼ 10⁴⁶ erg), neutron star–neutron star mergers (E_ej ∼ 10⁴⁹ erg), supernovae (E_ej ∼ 10⁵¹ erg), and hypernovae (E_ej ∼ 10⁵² erg). We find the mixing timescales for individual enrichment sources in our dwarf galaxy to be long (100 Myr–1 Gyr), with a clear trend of increasing homogeneity for the more energetic events. Given these timescales, we conclude that the spatial distribution and frequency of events are important drivers of abundance homogeneity on large scales; rare, low-E_ej events should be characterized by particularly broad abundance distributions. The source energy E_ej also correlates with the fraction of metals ejected in galactic winds, ranging anywhere from 60% at the lowest energy to 95% for hypernovae. We conclude by examining how the radial position, local ISM density, and global star formation rate influence these results.

Sunyaev–Zel'dovich (SZ) scaling relations have been used to test the self-similar prediction for massive galaxy clusters, but little attention has been given to individual galaxy groups. We investigate the scaling relations of galaxy groups and clusters near the North Ecliptic Pole using X-ray and SZ observations. This region of the sky is where both the ROSAT and Planck satellites achieved their deepest observations, permitting the investigation of lower mass systems. Our sample consists of 62 X-ray detected groups and clusters, spanning a mass range of ${10}^{13.4}{M}_{\odot }\lt \,{M}_{500}\lt {10}^{15}{M}_{\odot }$ and redshifts of 0.03 ≲ z ≲ 0.82. We extract the total SZ flux from unresolved Planck data and estimate the fraction of the SZ flux within R₅₀₀ assuming two different pressure profiles. The SZ scaling relations were derived using a Bayesian technique that accounts for censored data. We find a power law slope of ${1.73}_{-0.18}^{+0.19}$ for the Y_SZ–M₅₀₀ relation that is consistent with the self-similar prediction of 5/3. The slope of ${0.89}_{-0.08}^{+0.09}$ for the ${Y}_{\mathrm{SZ}}\mbox{--}{L}_{{\rm{X}},500}$ relation is in agreement with other observational studies but not the self-similar prediction of 5/4, and the ${Y}_{\mathrm{SZ}}\mbox{--}{Y}_{{\rm{X}}}$ relation lies below the 1:1 relation when the slope is fixed to unity. The determined scaling relations are dependent on the selected pressure profile, so resolved data are needed to determine the effects of active galactic nucleus feedback. In addition, we find a number of potential cluster candidates in the Planck Compton maps that were not identified in our X-ray sample.

Externally driven interstellar turbulence plays an important role in shaping the density structure in molecular clouds. Here we study the dynamical role of internally driven turbulence in a self-gravitating molecular cloud core. Depending on the initial conditions and evolutionary stages, we find that a self-gravitating core in the presence of gravity-driven turbulence can undergo constant, decelerated, and accelerated infall, and thus has various radial velocity profiles. In the gravity-dominated central region, a higher level of turbulence results in a lower infall velocity, a higher density, and a lower mass accretion rate. As an important implication of this study, efficient reconnection diffusion of magnetic fields against the gravitational drag naturally occurs due to the gravity-driven turbulence, without invoking externally driven turbulence.

A second peak in the extreme ultraviolet sometimes appears during the gradual phase of solar flares, which is known as the EUV late phase (ELP). Stereotypically ELP is associated with two separated sets of flaring loops with distinct sizes, and it has been debated whether ELP is caused by additional heating or extended plasma cooling in the longer loop system. Here we carry out a survey of 55 M-and-above GOES-class flares with ELP during 2010–2014. Based on the flare-ribbon morphology, these flares are categorized as circular-ribbon (19 events), two-ribbon (23 events), and complex-ribbon (13 events) flares. Among them, 22 events (40%) are associated with coronal mass ejections, while the rest are confined. An extreme ELP, with the late-phase peak exceeding the main-phase peak, is found in 48% of two-ribbon flares, 37% of circular-ribbon flares, and 31% of complex-ribbon flares, suggesting that additional heating is more likely present during ELP in two-ribbon than in circular-ribbon flares. Overall, cooling may be the dominant factor causing the delay of the ELP peak relative to the main-phase peak, because the loop system responsible for the ELP emission is generally larger than, and well separated from, that responsible for the main-phase emission. All but one of the circular-ribbon flares can be well explained by a composite "dome–plate" quasi-separatrix layer (QSL). Only half of these show a magnetic null point, with its fan and spine embedded in the dome and plate, respectively. The dome–plate QSL, therefore, is a general and robust structure characterizing circular-ribbon flares.

We report deep radio observations of nearby Type Ia supernovae (SNe Ia) with the electronic Multi-Element Radio Linked Interferometer Network and the Australia Telescope Compact Array. No detections were made. With standard assumptions for the energy densities of relativistic electrons going into a power-law energy distribution and the magnetic field strength (_e = _B = 0.1), we arrive at upper limits on mass-loss rate for the progenitor system of SN 2013dy (SN 2016coj, SN 2018gv, SN 2018pv, SN 2019np) of $\dot{M}\lesssim 12\,(2.8,1.3,2.1,1.7)\times {10}^{-8}\,{M}_{\odot }\,{\mathrm{yr}}^{-1}({v}_{w}/100\,\mathrm{km}\,{{\rm{s}}}^{-1})$, where v_w is the wind speed of the mass loss. To SN 2016coj, SN 2018gv, SN 2018pv, and SN 2019np we add radio data for 17 other nearby SNe Ia and model their nondetections. With the same model as described, all 21 SNe Ia have $\dot{M}\lesssim 4\times {10}^{-8}\,{M}_{\odot }\,{\mathrm{yr}}^{-1}({v}_{w}/100\,\mathrm{km}\,{{\rm{s}}}^{-1})$. We compare those limits with the expected mass-loss rates in different single-degenerate progenitor scenarios. We also discuss how information on _e and _B can be obtained from late observations of SNe Ia and the youngest SN Ia remnant detected in radio, G1.9+0.3, as well as stripped-envelope core-collapse SNe. We highlight SN 2011dh and argue for _e ≈ 0.1 and _B ≈ 0.0033. Finally, we discuss strategies to observe at radio frequencies to maximize the chance of detection, given the time since explosion, the distance to the SN, and the telescope sensitivity.

We examine the counts-in-cells (CiC) probability distribution functions (PDFs) that describe dark matter halos in the Dark Energy Universe Simulations (DEUS). We describe the measurements between redshifts z = 0 to z = 4 on both linear and nonlinear scales. The best fits of the gravitational quasi-equilibrium distribution (GQED), the negative binomial distribution (NBD), the Poisson-Lognormal distribution (PLN), and the Poisson-Lognormal distribution with a bias parameter (PLNB) are compared to simulations. The fits agree reasonably consistently over a range of redshifts and scales. To distinguish quintessence (RPCDM) and phantom (wCDM) dark energy from Λ dark energy, we present a new method that compares the model parameters of the CiC PDFs. We find that the mean and variance of the halo CiC on 2–25h⁻¹ Mpc scales between redshifts 0.65 < z < 4 show significant percentage differences for different dark energy cosmologies. On 15–25 h⁻¹ Mpc scales, the g parameter in NBD, ω parameter in PLN, and b and C_b parameters in PLNB show larger percentage differences for different dark energy cosmologies than on smaller scales. On 2–6 h⁻¹ Mpc scales, the kurtosis and the b parameter in the GQED show larger percentage differences for different dark energy cosmologies than on larger scales. For cosmologies explored in the DEUS, the percentage differences between these statistics for the RPCDM and wCDM dark energy cosmologies relative to ΛCDM generally increases with redshift from a few percent to significantly larger percentages at z = 4. Applying our method to simulations and galaxy surveys can provide a useful way to distinguish among dark energy models and cosmologies in general.

Enhancement of minor ions such as ³He and heavy ions in flare-associated solar energetic particle (SEP) events remains one of the major puzzles in heliophysics. In this work, we use 3D hybrid simulations (kinetic protons and fluid electrons) to investigate particle energization in a turbulent low-beta environment similar to solar flares. It is shown that in this regime the injected large-amplitude Alfvén waves develop into compressible and anisotropic turbulence, which efficiently heats thermal ions of different species. We find that temperature increase of heavy ions is inversely proportional to the charge-to-mass ratio, which is consistent with observations of impulsive SEP events. Further analysis reveals that ions are energized by interacting with nearly perpendicular magnetosonic waves near a proton inertial scale.

Fast radio bursts (FRBs) are highly energetic radio pulses from cosmological origins. Despite an abundance of detections, their nature remains elusive. At least a subset of FRBs is expected to repeat, as the volumetric FRB rate surpasses that of any known cataclysmic event, which has been confirmed by observations. One of the proposed mechanisms to generate repeating FRBs is supergiant pulses from young and highly spinning neutron stars (NSs), in which case FRBs could inherit the periodicity of their parent NS. Here we examine the consequences of such a population of periodic fast radio bursts (PFRBs). We calculate the rate and lifetime of PFRB progenitors, and find that each newly born highly spinning NS has to emit a number ${N}_{\mathrm{PFRB}}\sim {10}^{2}$ of detectable bursts during its active lifetime of $\tau \sim 100$ yr, after which it becomes too dim and crosses a PFRB "death line" analogous to the pulsar one. We propose several tests of this hypothesis. First, the period of PFRBs would increase over time, and their luminosity would decrease, due to the NS spin-down. Second, PFRBs may show modest amounts of rotation measure, given the lack of expelled matter from the pulsar, as opposed to the magnetar-sourced FRBs proposed to explain the first repeater FRB 121102. As an example, we study whether the second confirmed repeater (FRB 180814) is a PFRB, given the preference for an inter-pulse separation of 13 ms within its sub-bursts. We show that, if confirmed, this period would place FRB 180814 in a different category as FRB 121102. We develop tests that would identify—and characterize—the prospective population of PFRBs.

Screened modified gravity (SMG) is a unified theoretical framework that describes scalar–tensor gravity with a screening mechanism. Based on the gravitational-wave (GW) waveform derived in our previous work, in this article we investigate the potential constraints on SMG theory through GW observation by future spaceborne GW detectors, including the Laser Interferometer Space Antenna (LISA), TianQin, and Taiji. We find that, for the extreme-mass-ratio inspirals (EMRIs) consisting of a massive black hole and a neutron star, if the EMRIs are at the Virgo cluster, the GW signals can be detected by the detectors at quite high significance level, and the screened parameter _NS can be constrained at about ${ \mathcal O }({10}^{-5})$, which is more than one order of magnitude tighter than the potential constraint given by a ground-based Einstein telescope. However, for the EMRIs consisting of a massive black hole and a white dwarf, it is more difficult to detect them than in the previous case. For the specific SMG models, including chameleon, symmetron, and dilaton, we find these constraints are complementary to that from the Cassini experiment, but weaker than those from lunar laser ranging observations and binary pulsars, due to the strong gravitational potentials on the surface of neutron stars. By analyzing the deviation of the GW waveform in SMG from that in general relativity, as anticipated, we find the dominant contribution of the SMG constraint comes from the correction terms in the GW phases, rather than the extra polarization modes or the correction terms in the GW amplitudes.

A multiwavelength temporal and spectral analysis of flares of 3C 279 during 2017 November–2018 July are presented in this work. Three bright gamma-ray flares were observed simultaneously in X-ray and optical/UV along with a prolonged quiescent state. A "harder-when-brighter" trend is observed in both gamma-rays and X-rays during the flaring period. The gamma-ray light curve for all the flares is binned in one day time bins and a day-scale variability is observed. Variability time constrains the size and location of the emission region to 2.1 × 10¹⁶ cm and 4.4 × 10¹⁷ cm, respectively. The fractional variability reveals that the source is more than 100% variable in gamma-rays and it decreases toward the lower energy. A cross-correlation study of the emission from different wavebands is done using the discrete correlations function method, which shows a strong correlation between them without any time lags. The zero time lag between different wavebands suggests their cospatial origin. This is the first time 3C 279 has shown a strong correlation between gamma-ray and X-ray emission with zero time lag. A single-zone emission model was adopted to model the multiwavelength spectral energy distributions by using the publicly available code GAMERA. The study reveals that a higher jet power in electrons is required to explain the gamma-ray flux during the flaring state, as much as 10 times that required for the quiescent state. However, more jet power in the magnetic field has been observed during the quiescent state compared to the flaring state.

We analyzed high-angular resolution 45.5 GHz images of the W49 North massive star-forming region obtained in 1998 and 2016 with the Very Large Array. Most of the ultracompact H ii regions show no detectable changes over the time interval of the observations. However, subcomponents B1, B2, G2a, and G2c have increased its peak flux densities by values in the range of 3.8%–21.4%. Most interestingly, the cometary region C clearly shows proper motions that at the distance of the region are equivalent to a velocity of 76 ± 6 km s⁻¹ in the plane of the sky. We interpret this region as the ionized bowshock produced by a runaway O6 ZAMS star that was ejected from the eastern edge of Welch's ring about 6400 yr ago.

Ultraluminous X-ray sources (ULXs) are a class of accreting compact objects with X-ray luminosities above 10³⁹ erg s⁻¹. The ULX population counts several hundred objects but only a fraction are well studied. Here we present a detailed analysis of all ULXs hosted in the galaxy NGC 7456. It was observed in X-rays only once in the past (in 2005) by XMM-Newton. but the observation was short and strongly affected by high background. In 2018, we obtained a new, deeper (∼90 ks) XMM-Newton observation that allowed us to perform a detailed characterization of the ULXs hosted in the galaxy. ULX-1 and ULX-2, the two brightest objects (L_X ∼ 6−10 × 10³⁹ erg s⁻¹), have spectra that can be described by a model with two thermal components, as often found in ULXs. ULX-1 also shows one order of magnitude in flux variability on short-term timescales (hundreds to thousands of kiloseconds). The other sources (ULX-3 and ULX-4) show flux changes of at least an order of magnitude, and these objects may be candidate transient ULXs, although longer X-ray monitoring or further studies are required to ascribe them to the ULX population. In addition, we found a previously undetected source that might be a new candidate ULX (labeled as ULX-5), with a luminosity of ∼10³⁹ erg s⁻¹ and hard power-law spectral shape, whose nature is still unclear and for which a background active galactic nucleus cannot be excluded. We discuss the properties of all the ULXs in NGC 7456 within the framework of super-Eddington accretion onto stellar-mass compact objects. Although no pulsations were detected, we cannot exclude that the sources host neutron stars.

We report the results of high-resolution molecular line observations of the high-velocity compact cloud HCN–0.085–0.094 with the Atacama Large Millimeter/submillimeter Array. The HCN J = 4–3, HCO⁺J = 4–3, and CS J = 7–6 line images reveal that HCN–0.085–0.094 consists mainly of three small clumps with extremely broad velocity widths. Each of the three clumps has a 5.5 GHz radio continuum counterpart in its periphery toward Sgr A*. The positional relationship indicates that their surfaces have been ionized by ultraviolet photons from young stars in the central cluster, suggesting the clumps are in close proximity to the Galactic nucleus. One of the three clumps has a ring-like structure with a very steep velocity gradient. This kinematical structure suggests an orbit around a point-like object with a mass of ∼10⁴M_⊙. The absence of stellar counterparts indicates that the point-like object may be a quiescent black hole. This discovery adds another intermediate-mass black hole candidate in the central region of our Galaxy.

We report a $5.3\sigma$ detection of the gravitational lensing effect of cosmic voids from the Baryon Oscillation Spectroscopic Data Release 12 seen in the Planck 2018 cosmic microwave background (CMB) lensing convergence map. To make this detection, we introduce new optimal techniques for void stacking and filtering of the CMB maps, such as binning voids by a combination of their observed galaxy density and size to separate those with distinctive lensing signatures. We calibrate theoretical expectations for the void lensing signal using mock catalogs generated in a suite of 108 full-sky lensing simulations from Takahashi et al. Relative to these templates, we measure the lensing amplitude parameter in the data to be A_L = 1.10 ± 0.21 using a matched-filter stacking technique and confirm it using an alternative Wiener-filtering method. We demonstrate that the result is robust against thermal Sunyaev–Zel'dovich contamination and other sources of systematics. We use the lensing measurements to test the relationship between the matter and galaxy distributions within voids and show that the assumption of linear bias with a value consistent with galaxy clustering results is discrepant with observation at ∼3σ; we explain why such a result is consistent with simulations and previous results, and is expected as a consequence of void selection effects. We forecast the potential for void CMB lensing measurements in future data from the Advanced ACT, Simons Observatory, and CMB-S4 experiments, showing that, for the same number of voids, the achievable precision improves by a factor of more than 2 compared to Planck.

Astrophysical observations provide a unique opportunity to test possible signatures of Lorentz invariance violation (LIV), due to the high energies and long distances involved. In quantum theory of gravity, one may expect the modification of the dispersion relation between energy and momentum for photons, which can be probed with the time lag (the arrival time delay between light curves in different energy bands) of gamma-ray bursts (GRBs). In this paper, by using the detailed time delay measurements of GRB 160625B at different energy bands, as well as 23 time delay GRBs covering the redshift range of z = 0.168–2.5 (which were measured at different energy channels from the light curves), we propose an improved model-independent method (based on the newly compiled sample of H(z) measurements) to probe the energy-dependent velocity due to the modified dispersion relation for photons. In the framework of a more complex and reasonable theoretical expression to describe the time delays, our results imply that the intrinsic time lags can be better described with more GRB time delay data. More importantly, through direct fitting of the time delay measurements of a sample of GRBs, our limit on the LIV energy scale is comparable to that with unknown constant for the intrinsic time lag, much lower than the Planck energy scale in both linear LIV and quadratic LIV cases.

Small particles (meter to kilometer sized) can drift inward through a protoplanetary disk owing to their interaction with a gaseous nebula. If planets exist, these particles can get captured in mean motion resonance (MMR) and, if massive, exchange angular momentum with the planets. While dependent on the total mass in small inward-drifting particles captured, the main result out of such resonant angular momentum exchange is inward planet shepherding. However, it is not clear what the real dynamics of a large number of massive particles in MMR would be when collisional effects are included. Therefore, we studied the capture mechanism and collisional evolution of a swarm of massive inward-drifting particles in MMRs with planets. Due to the confined space of an MMR, captured massive particles can rapidly collisionally evolve. Our main results show that, if massive particles are assumed to be rocky, collisions make the swarm of particles decrease in size. In this case, as their gas drag properties change (smaller particles drift faster through the gas nebula), they eventually leave the MMR. On the other hand, if massive particles are assumed to be 10, 100, or 1000 times stronger (harder to break) than rocky particles, they instead grow. In this situation, the drifting particles slow down (r ≳ 1–5 km) or even stop (r ≳ 5–10 km) their inward drift. We conclude that, although some angular momentum exchange may exist, in no cases studied here did the massive inward-drifting particles significantly change the orbit of the planet.

We combine observations from the Atacama Large Millimeter/submillimeter Array and the NOrthern Extended Millimeter Array to assess the redshift and to study the star formation conditions in AzTEC2, one of the brightest submillimeter galaxies (SMGs) in the COSMOS field (${S}_{1.1\mathrm{mm}}=10.5\pm 1.4$ mJy). Our high-resolution observations confirm that AzTEC2 splits into two components (namely AzTEC2-A and AzTEC2-B) for which we detect [C ii] and ¹²CO(5 → 4) line emission, implying a redshift of 4.626 ± 0.001 (4.633 ± 0.001) for AzTEC2-A (AzTEC2-B) and ruling out previous associations with a galaxy at $z\sim 1$. We use the ¹²CO(5 → 4) line emission and adopt typical SMG-like gas excitation conditions to estimate the molecular gas mass, which is ${M}_{\mathrm{gas}}({\alpha }_{\mathrm{CO}}/2.5)=2.1\pm 0.4\,\times \,{10}^{11}\,{M}_{\odot }$ for AzTEC2-A, and a factor four lower for AzTEC2-B. With the infrared-derived star formation rate of AzTEC2-A ($1920\pm 100\,{M}_{\odot }$ yr⁻¹) and AzTEC2-B ($710\pm 35\,{M}_{\odot }$ yr⁻¹), they both will consume their current gas reservoir within (30–200) Myr. We find evidence of a rotation-dominated [C ii] disk in AzTEC2-A, with a deprojected rotational velocity of ${v}_{\mathrm{rot}}(i=39^\circ )=660\pm 130$ km s⁻¹, velocity dispersion $\lesssim 100$ km s⁻¹, and dynamical mass of ${M}_{\mathrm{dyn}}(i=39^\circ )={2.6}_{-0.9}^{+1.2}\times {10}^{11}\,{M}_{\odot }$. We propose that an elevated gas accretion rate from the cosmic web might be the main driver of the intense levels of star formation in AzTEC2-A, which might be further enhanced by gravitational torques induced by its minor companion (AzTEC2-B). These results strengthen the picture whereby the population of single-dish selected SMGs is rather heterogeneous, including a population of pairs of massive, highly active galaxies in a pre-coalescence phase.

Improvements to the precision of measurements of cosmological parameters with Type Ia supernovae (SNe Ia) are expected to come from large photometrically identified (photometric) supernova (SN) samples. Here we reanalyze the Sloan Digital Sky Survey (SDSS) photometric SN sample, with roughly 700 high-quality, likely but unconfirmed SNe Ia light curves, to develop new analysis tools aimed at evaluating systematic uncertainties on the dark energy equation-of-state parameter w. Since we require a spectroscopically measured host-galaxy redshift for each SN, we determine the associated selection efficiency of host galaxies in order to simulate bias corrections. We determine that the misassociation rate of host galaxies is 0.6%; ignoring this effect in simulated bias corrections leads to a w-bias of Δw = +0.0007, where w is evaluated from SNe Ia and priors from measurements of baryon acoustic oscillations and the cosmic microwave background. We assess the uncertainty in our modeling of the host-galaxy selection efficiency and find the associated w uncertainty to be −0.0072. Finally, we explore new core-collapse (CC) models in simulated training samples and find that adjusting the CC luminosity distribution to be in agreement with previous Pan-STARRS analyses yields a better match to the SDSS data. The impact of ignoring this adjustment is Δw = −0.0109; the impact of replacing the new CC models with those used by Pan-STARRS is Δw = −0.0028. These systematic uncertainties are subdominant to the statistical constraints from the SDSS sample, but must be considered in future photometric analyses of large SN samples such as those from the Dark Energy Survey (DES), the Large Synoptic Survey Telescope (LSST), and the Wide Field Infrared Survey Telescope (WFIRST).

The formation and evolution of galaxies are highly dependent on the dynamics of stars and gas, which is governed by the underlying law of gravity. To investigate how the formation and evolution of galaxies take place in Milgromian gravity (MOND), we present full hydrodynamical simulations with the Phantom of Ramses code. These are the first-ever galaxy formation simulations done in MOND with detailed hydrodynamics, including star formation, stellar feedback, radiative transfer, and supernovae. These models start from simplified initial conditions, in the form of isolated, rotating gas spheres in the early universe. These collapse and form late-type galaxies obeying several scaling relations, which was not a priori expected. The formed galaxies have a compact bulge and a disk with exponentially decreasing surface mass density profiles and scale lengths consistent with observed galaxies, as well as vertical stellar mass distributions with distinct exponential profiles (thin and thick disk). This work thus shows for the first time that disk galaxies with exponential profiles in both gas and stars are a generic outcome of collapsing gas clouds in MOND. These models have a slight lack of stellar angular momentum because of their somewhat compact stellar bulge, which is connected to the simple initial conditions and the negligible later gas accretion. We also analyze how the addition of more complex baryonic physics changes the resulting main properties of the models and find this to be negligibly so in the Milgromian framework.

We present an improved, hybrid CPU-GPU atmospheric retrieval code, Helios-r2, which is applicable to medium-resolution emission spectra of brown dwarfs, in preparation for precision atmospheric spectroscopy in the era of the James Webb Space Telescope. The model is available as open-source code on the Exoclimes Simulation Platform. We subject Helios-r2 to a battery of tests of varying difficulty. The simplest test involves a mock retrieval on a forward model generated using the same radiative transfer technique, the same implementation of opacities, and the same chemistry model. The least trivial test involves a mock retrieval on synthetic spectra from the Sonora model grid, which uses a different radiative transfer technique, a different implementation of opacities, and a different chemistry model. A calibration factor, which is included to capture uncertainties in the brown dwarf radius, distance to the brown dwarf and flux calibration of the spectrum, may compensate, sometimes erroneously, for discrepancies in modeling choices and implementation. We analyze spectra of the benchmark brown dwarf GJ 570 D and the binary brown dwarf companions in the Epsilon Indi system. The retrieved surface gravities are consistent with previous studies and/or values inferred from dynamical masses (for Epsilon Indi Ba and Bb only). There remains no clear criterion on how to reject unphysical values of the retrieved brown dwarf radii. The inferred radii and corresponding masses should be taken with great caution. The retrieved carbon-to-oxygen ratios and metallicity depend on whether chemical equilibrium is assumed.

Eccentric nuclear disks (ENDs) are a type of star cluster in which the stars lie on eccentric, apsidally aligned orbits in a disk around a central supermassive black hole. These disks can produce a high rate of tidal disruption events via secular gravitational torques. Previous studies of ENDs have included stars with only one mass. Here, we present the first study of an END with two stellar species. We show that ENDs show radial mass segregation consistent with previous results from other cluster types. Additionally, ENDs show vertical mass segregation by which the heavy stars sink to lower inclinations than light stars. These two effects cause heavy stars to be more susceptible to tidal disruption, which can be seen in the higher fraction of heavy stars that are disrupted compared to light stars.

The James Webb Space Telescope (JWST) is expected to revolutionize the field of exoplanets. The broad wavelength coverage and the high sensitivity of its instruments will allow characterization of exoplanetary atmospheres with unprecedented precision. Following the Call for the Cycle 1 Early Release Science Program, the Transiting Exoplanet Community was awarded time to observe several targets, including WASP-43b. The atmosphere of this hot Jupiter has been intensively observed but still harbors some mysteries, especially concerning the day–night temperature gradient, the efficiency of the atmospheric circulation, and the presence of nightside clouds. We will constrain these properties by observing a full orbit of the planet and extracting its spectroscopic phase curve in the 5–12 μm range with JWST/MIRI. To prepare for these observations, we performed extensive modeling work with various codes: radiative transfer, chemical kinetics, cloud microphysics, global circulation models, JWST simulators, and spectral retrieval. Our JWST simulations show that we should achieve a precision of 210 ppm per 0.1 μm spectral bin on average, which will allow us to measure the variations of the spectrum in longitude and measure the nightside emission spectrum for the first time. If the atmosphere of WASP-43b is clear, our observations will permit us to determine if its atmosphere has an equilibrium or disequilibrium chemical composition, eventually providing the first conclusive evidence of chemical quenching in a hot Jupiter atmosphere. If the atmosphere is cloudy, a careful retrieval analysis will allow us to identify the cloud composition.

Type IIP and Type IIL supernovae are defined on the basis of their light curves, but the spectral criteria for distinguishing these two types of supernovae (SNe) remain unclear. We propose a spectral classification method. First, we subtract the principal components of different wavelength bands in the spectra based on the functional principal components analysis method. Then, we use support vector machine and artificial neural network to classify these two types of SNe. The best F1_Score of our classifier is 0.871 for SNe IIL, and 0.974 for SNe IIP. We found that by only using the H_α line at 6150–6800 Å for classification, the F1_Score up to 0.961 for Type IIP, and 0.818 for Type IIL SNe can be obtained. These results indicate that the profile of the H_α spectral line is the key to distinguishing the two types of SNe.

Observations of intermediate mass (IM) star formation are expected to highlight the transition between the formation processes of its low and high-mass (HM) counterparts. ${{\rm{H}}}_{2}^{18}{\rm{O}}$ and ${{\rm{H}}}_{2}^{16}{\rm{O}}$ observations of the IM star formation region NGC 7129 FIRS 2 were obtained with the Heterodyne Instrument for the Far-Infrared aboard the Herschel Space Observatory; most as part of the WISH key-program. The radiative transfer program RATRAN was used to model water emission from the envelope of this star-forming region. We consider the envelope in two regions, inner and outer envelope, which are separated by the water freeze-out radius. An outer envelope ortho-H${}_{2}^{18}$O/H₂ abundance was determined to be 3.5 ± 0.3 × 10⁻¹¹, and an outer turbulent velocity was determined to be 2.25  ± 0.25 km s⁻¹. The outer envelope ortho-H₂¹⁶O/H₂ and para-H₂¹⁶O/H₂ abundances were determined to be 1.5 ± 0.5 × 10⁻⁸ and 4.5 ± 0.5 × 10⁻⁹, respectively. The inner envelope abundances and turbulent velocity could not be constrained due to increased optical depth. The derived values are consistent with those found by low-mass (LM) and HM young stellar object studies of water. While the line shapes and intensities of these lines are more similar to the spectral lines found for LM objects, the turbulent velocity is closer to that seen in HM objects. Lastly, we present a simple visualization tool that we created to show that these abundance results, particularly the limited extent probed by these lines, should not have been a surprise. This tool can be very useful in planning future molecular line observations.