Table of contents

Coronal condensation and rain are a crucial part of the mass cycle between the corona and chromosphere. In some cases, condensation and subsequent rain originate in the magnetic dips formed during magnetic reconnection. This provides a new and alternative formation mechanism for coronal rain. Until now, only off-limb, rather than on-disk, condensation events during reconnection have been reported. In this paper, employing extreme-ultraviolet (EUV) images of the Solar Terrestrial Relations Observatory (STEREO) and Solar Dynamics Observatory (SDO), we investigate the condensations facilitated by reconnection from 2011 July 14–15, when STEREO was in quadrature with respect to the Sun–Earth line. Above the limb, in STEREO/EUV Imager (EUVI) 171 Å images, higher-lying open structures move downward, reconnect with the lower-lying closed loops, and form dips. Two sets of newly reconnected structures then form. In the dips, bright condensations occur in the EUVI 304 Å images repeatedly, which then flow downward to the surface. In the on-disk observations by SDO/Atmospheric Imaging Assembly (AIA) in the 171 Å channel, these magnetic structures are difficult to identify. Dark condensations appear in the AIA 304 Å images, and then move to the surface as on-disk coronal rain. The cooling and condensation of coronal plasma is revealed by the EUV light curves. If only the on-disk observations were be available, the relation between the condensations and reconnection, shown clearly by the off-limb observations, could not be identified. Thus, we suggest that some on-disk condensation events seen in transition region and chromospheric lines may be facilitated by reconnection.

In November 2020, the Swift team announced an update to the UltraViolet and Optical Telescope calibration to correct for the loss of sensitivity over time. This correction affects observations in the three near-ultraviolet (UV) filters, by up to 0.3 mag in some cases. As UV photometry is critical to characterizing tidal disruption events (TDEs) and other peculiar nuclear outbursts, we recomputed published Swift data for TDEs and other singular nuclear outbursts with Swift photometry in 2015 or later as a service to the community. Using archival UV, optical, and infrared photometry, we ran host SED fits for each host galaxy. From these, we computed synthetic host magnitudes and host-galaxy properties. We calculated host-subtracted magnitudes for each transient and computed blackbody fits. In addition to the nuclear outbursts, we include the ambiguous transient ATLAS18qqn (AT2018cow), which has been classified as a potential TDE on an intermediate-mass black hole. Finally, with updated bolometric light curves, we recover the relationship of Hinkle et al., where more-luminous TDEs decay more slowly than less-luminous TDEs, with decreased scatter compared to the original relationship.

Parker first proposed (1972) that coronal heating was the necessary outcome of an energy flux caused by the tangling of coronal magnetic field lines by photospheric flows. In this paper we discuss how this model has been modified by subsequent numerical simulations outlining in particular the substantial differences between the "nanoflares" introduced by Parker and "elementary events," defined here as small-scale spatially and temporally isolated heating events resulting from the continuous formation and dissipation of field-aligned current sheets within a coronal loop. We present numerical simulations of the compressible 3D MHD equations using the HYPERION code. We use two clustering algorithms to investigate the properties of the simulated elementary events: an IDL implementation of a density-based spatial clustering of applications with noise technique, and our own physical distance clustering algorithm. We identify and track elementary heating events in time, both in temperature and in Joule heating space. For every event we characterize properties such as density, temperature, volume, aspect ratio, length, thickness, duration, and energy. The energies of the events are in the range of 10¹⁸–10²¹ erg, with durations shorter than 100 s. A few events last up to 200 s and release energies up to 10²³ erg. While high temperatures are typically located at the flux tube apex, the currents extend all the way to the footpoints. Hence, a single elementary event cannot at present be detected. The observed emission is due to the superposition of many elementary events distributed randomly in space and time within the loop.

It has been proposed that spin-polarized cosmic radiation can induce asymmetric changes in helical biopolymers that may account for the emergence of biological homochirality. The parity violation in the weak interaction has direct consequences on the transport of polarization in cosmic ray showers. In this paper, we show that muons retain their polarization down to energies at which they can initiate enantioselective mutagenesis. Therefore, muons are most likely to succeed in establishing the connection between broken symmetries in the standard model of particle physics and that found in living organisms. We calculate the radiation doses deposited by primary and secondary cosmic rays at various prime targets for the searches of life in the solar system: Mars, Venus, Titan, icy moons and planetesimals, and discuss the implications for the enantioselective mutagenesis proposed as to be the driver of homochiralization. Earth is unusual in that spin-polarized muons dominate the cosmic radiation at its surface.

The past decade has seen impressive progress in the detection of z > 7 galaxies with the Hubble Space Telescope; however, little is known about their properties. The James Webb Space Telescope will revolutionize the high-z field by providing near-IR (i.e., rest-frame optical) data of unprecedented depth and spatial resolution. Measuring galaxy quantities such as resolved stellar ages or gas metallicity gradients traditionally requires spectroscopy, as broadband imaging filters are generally too coarse to fully isolate diagnostics such as the 4000 Å (rest-frame) break, continuum emission from aged stars, and key emission lines (e.g., [O ii], [O iii], Hβ). However, in this paper, we show that adding NIRCam images through a strategically chosen medium-band filter to common wide-band filter sets adopted by ERS and GTO programs delivers tighter constraints on these galactic properties. To constrain the choice of filter, we perform a systematic investigation of which combinations of wide-band filters from ERS and GTO programs and single medium-band filters offer the tightest constraints on several galaxy properties at redshifts z ∼ 7–11. We employ the JAGUAR extragalactic catalogs to construct statistical samples of physically motivated mock photometry and conduct SED-fitting procedures to evaluate the accuracy of galaxy property (and photo-z) recovery with a simple star formation history model. We find that adding >4.1 μm medium filters at comparable depth to the broadband filters can significantly improve photo-zs and yield close to order-of-magnitude improvements in the determination of quantities such as stellar ages, metallicities, SF-related quantities, and emission-line fluxes at z ∼ 8. For resolved sources, the proposed approach enables the spatially resolved determination of these quantities that would be prohibitive with slit spectroscopy.

We construct empirical models of star-forming galaxy evolution assuming that individual galaxies evolve along well-known scaling relations between stellar mass, gas mass, and star formation rate following a simple description of chemical evolution. We test these models by a comparison with observations and detailed Magneticum high-resolution hydrodynamic cosmological simulations. Galaxy star formation rates, stellar masses, gas masses, ages, interstellar medium, and stellar metallicities are compared. It is found that these simple look-back models capture many of the crucial aspects of galaxy evolution reasonably well. Their key assumption of a redshift-dependent power-law relationship between galaxy interstellar medium gas mass and stellar mass is in agreement with the outcome of the complex Magneticum simulations. Star formation rates decline toward lower redshift not because galaxies are running out of gas, but because the fraction of the cold interstellar medium gas, which is capable of producing stars, becomes significantly smaller. Gas accretion rates in both model approaches are of the same order of magnitude. Metallicity in the Magneticum simulations increases with the ratio of stellar mass to gas mass as predicted by the look-back models. The mass–metallicity relationships agree, and the star formation rate dependence of these relationships is also reproduced. We conclude that these simple models provide a powerful tool for constraining and interpreting more complex models based on cosmological simulations and for population synthesis studies analyzing the integrated spectra of stellar populations.

The interstellar turbulence is magnetized and thus anisotropic. The anisotropy of turbulent magnetic fields and velocities is imprinted in the related observables, rotation measures (RMs), and velocity centroids (VCs). This anisotropy provides valuable information on both the direction and strength of the magnetic field. However, its measurement is difficult, especially in highly supersonic turbulence in cold interstellar phases, due to the distortions by isotropic density fluctuations. By using 3D simulations of supersonic and sub-Alfvénic magnetohydrodynamic (MHD) turbulence, we find that the problem can be alleviated when we selectively sample the volume filling low-density regions in supersonic MHD turbulence. Our results show that in these low-density regions the anisotropy of RM and VC fluctuations depends on the Alfvénic Mach number as ${M}_{{\rm{A}}}^{-4/3}$. This anisotropy−M_A relation is theoretically expected for sub-Alfvénic MHD turbulence and confirmed by our synthetic observations of ¹²CO emission. It provides a new method for measuring the plane-of-the-sky magnetic fields in cold interstellar phases.

The underlying distribution of galaxies' dust spectral energy distributions (SEDs) (i.e., their spectra reradiated by dust from rest-frame ∼3 μm to 3 mm) remains relatively unconstrained owing to a dearth of far-IR/(sub)millimeter data for large samples of galaxies. It has been claimed in the literature that a galaxy's dust temperature—observed as the wavelength where the dust SED peaks (λ_peak)—is traced most closely by its specific star formation rate (sSFR) or parameterized "distance" to the SFR–M_⋆ relation (the galaxy "main sequence"). We present 024 resolved 870 μm ALMA dust continuum observations of seven z = 1.4–4.6 dusty star-forming galaxies chosen to have a large range of well-constrained luminosity-weighted dust temperatures. We also draw on similar-resolution dust continuum maps from a sample of ALESS submillimeter galaxies from Hodge et al (2016). We constrain the physical scales over which the dust radiates and compare those measurements to characteristics of the integrated SED. We confirm significant correlations of λ_peak with both L_IR (or SFR) and Σ_IR (∝SFR surface density). We investigate the correlation between log₁₀(λ_peak) and log₁₀(Σ_IR) and find the relation to hold as would be expected from the Stefan–Boltzmann law, or the effective size of an equivalent blackbody. The correlations of λ_peak with sSFR and distance from the SFR–M_⋆ relation are less significant than those for Σ_IR or L_IR; therefore, we conclude that the more fundamental tracer of galaxies' luminosity-weighted integrated dust temperatures are indeed their star formation surface densities in line with local universe results, which relate closely to the underlying geometry of dust in the interstellar medium.

We study the behavior and properties of the solar wind using a 2.5D Alfvén wave (AW)-driven wind model. We first systematically compare the results of an AW-driven wind model with a polytropic approach. Polytropic magnetohydrodynamic wind models are thermally driven, while AWs act as additional acceleration and heating mechanisms in the AW-driven model. We confirm that an AW-driven model is required to reproduce the observed bimodality of slow and fast solar winds. We are also able to reproduce the observed anticorrelation between the terminal wind velocity and the coronal source temperature with the AW-driven wind model. We also show that the wind properties along an 11 yr cycle differ significantly from one model to the other. The AW-driven model again shows the best agreement with observational data. Indeed, solar surface magnetic field topology plays an important role in the AW-driven wind model, as it enters directly into the input energy sources via the Poynting flux. On the other hand, the polytropic wind model is driven by an assumed pressure gradient; thus, it is relatively less sensitive to the surface magnetic field topology. Finally, we note that the net torque spinning down the Sun exhibits the same trends in the two models, showing that the polytropic approach still correctly captures the essence of stellar winds.

In this work, we derive magnetic toroids from surface magnetograms by employing a novel optimization method, based on the trust region reflective algorithm. The toroids obtained in this way are combinations of Fourier modes (amplitudes and phases) with low longitudinal wavenumbers. The optimization also estimates the latitudinal width of the toroids. We validate the method using synthetic data, generated as random numbers along a specified toroid. We compute the shapes and latitudinal widths of the toroids via magnetograms, generally requiring several m's to minimize residuals. A threshold field strength is chosen to include all active regions in the magnetograms for toroid derivation, while avoiding non-contributing weaker fields. Higher thresholds yield narrower toroids, with an m = 1 dominant pattern. We determine the spatiotemporal evolution of toroids by optimally weighting the amplitudes and phases of each Fourier mode for a sequence of five Carrington Rotations (CRs) to achieve the best amplitude and phases for the middle CR in the sequence. Taking more than five causes "smearing" or degradation of the toroid structure. While this method applies no matter the depth at which the toroids actually reside inside the Sun, by comparing their global shape and width with analogous patterns derived from magnetohydrodynamic (MHD) tachocline shallow water model simulations, we infer that their origin is at/near the convection zone base. By analyzing the "Halloween" storms as an example, we describe features of toroids that may have caused the series of space weather events in 2003 October–November. Calculations of toroids for several sunspot cycles will enable us to find similarities/differences in toroids for different major space weather events.

We present a direct comparison of the Pan-Andromeda Archaeological Survey (PAndAS) observations of the stellar halo of M31 with the stellar halos of six galaxies from the Auriga simulations. We process the simulated halos through the Auriga2PAndAS pipeline and create PAndAS-like mocks that fold in all observational limitations of the survey data (foreground contamination from the Milky Way stars, incompleteness of the stellar catalogs, photometric uncertainties, etc.). This allows us to study the survey data and the mocks in the same way and generate directly comparable density maps and radial density profiles. We show that the simulations are overall compatible with the observations. Nevertheless, some systematic differences exist, such as a preponderance for metal-rich stars in the mocks. While these differences could suggest that M31 had a different accretion history or has a different mass compared with the simulated systems, it is more likely a consequence of an underquenching of the star formation history of galaxies, related to the resolution of the Auriga simulations. The direct comparison enabled by our approach offers avenues to improve our understanding of galaxy formation as they can help pinpoint the observable differences between observations and simulations. Ideally, this approach will be further developed through an application to other stellar halo simulations. To facilitate this step, we release the pipeline to generate the mocks, along with the six mocks presented and used in this contribution.

Detections of the tidal disruption flares (TDFs) of stars by supermassive black holes (SMBHs) are rapidly accumulating as optical surveys improve. These detections may provide constraints on SMBH demographics, stellar dynamics, and stellar evolution in galaxies. To maximize this scientific impact, we require a better understanding of how astrophysical parameters interact with survey selection effects in setting the properties of detected flares. We develop a framework for modeling the distributions of optical TDF detections in surveys across attributes of the host galaxies and the flares themselves. This model folds in effects of the stellar disruption rate in each galaxy, the flare luminosity and temperature distributions, the effects of obscuration and reddening by dust in the host galaxy, and survey selection criteria. We directly apply this model to the sample of TDFs detected by the Zwicky Transient Facility, and find that the overall flare detection rate is in line with simple theoretical expectation. The model can also reproduce the distribution of total stellar mass and redshift of the host galaxies, but fails to match all details of the detected flares, such as their luminosity and temperature distributions. We also find that dust obscuration likely plays an important role in suppressing the TDF detection rate in star-forming galaxies. While we do not find that the unusual preference of TDFs to have hosts in post-starburst galaxies in the "green valley" can be entirely explained by selection effects, our model can help to quantify the true rate enhancement in those galaxies.

Active galactic nuclei (AGNs) are powered by geometrically thin accretion disks surrounding a central supermassive black hole. Here we explore the evolution of stars embedded in these extreme astrophysical environments (AGN stars). Because AGN disks are much hotter and denser than most components of the interstellar medium, AGN stars are subject to very different boundary conditions than normal stars. They are also strongly affected by both mass accretion, which can run away given the vast mass of the disk, and mass loss due to super-Eddington winds. Moreover, chemical mixing plays a critical role in the evolution of these stars by allowing fresh hydrogen accreted from the disk to mix into their cores. We find that, depending on the local AGN density and sound speed and the duration of the AGN phase, AGN stars can rapidly become very massive (M > 100 M_⊙). These stars undergo core collapse, leave behind compact remnants, and contribute to polluting the disk with heavy elements. We show that the evolution of AGN stars can have a profound impact on the evolution of AGN metallicities, as well as the production of gravitational wave sources observed by LIGO-Virgo. We point to our Galactic Center as a region well suited to testing some of our predictions for this exotic stellar evolutionary channel.

A key component of the baryon cycle in galaxies is the depletion of metals from the gas to the dust phase in the neutral interstellar medium (ISM). The METAL (Metal Evolution, Transport, and Abundance in the Large Magellanic Cloud) program on the Hubble Space Telescope acquired UV spectra toward 32 sight lines in the half-solar metallicity LMC, from which we derive interstellar depletions (gas-phase fractions) of Mg, Si, Fe, Ni, S, Zn, Cr, and Cu. The depletions of different elements are tightly correlated, indicating a common origin. Hydrogen column density is the main driver for depletion variations. Correlations are weaker with volume density, probed by C i fine-structure lines, and distance to the LMC center. The latter correlation results from an east–west variation of the gas-phase metallicity. Gas in the east, compressed side of the LMC encompassing 30 Doradus and the southeast H i over-density is enriched by up to +0.3 dex, while gas in the west side is metal deficient by up to −0.5 dex. Within the parameter space probed by METAL, no correlation with molecular fraction or radiation-field intensity are found. We confirm the factor of three to four increase in dust-to-metal and dust-to-gas ratios between the diffuse (log N(H) ∼ 20 cm⁻²) and molecular (log N(H) ∼ 22 cm⁻²) ISM observed from far-infrared, 21 cm, and CO observations. The variations of dust-to-metal and dust-to-gas ratios with column density have important implications for the sub-grid physics of chemical evolution, gas and dust mass estimates throughout cosmic times, and for the chemical enrichment of the Universe measured via spectroscopy of damped Lyα systems.

We develop a new equation-of-state (EOS) table involving thermal (anti)kaons, Bose–Einstein condensate of K⁻ mesons, and Λ-hyperons for core-collapse supernova and neutron star merger simulations. This EOS table is based on a finite-temperature, density-dependent relativistic hadron field theory where baryon–baryon interaction is mediated by scalar σ, vector ω, and ρ mesons, using the parameter set DD2 for nucleons. The repulsive hyperon–hyperon interaction is mediated by an additional strange ϕ meson. The EOS for the K⁻ condensed matter is also calculated within the framework of the relativistic mean field model, whereas the low-density, inhomogeneous matter is calculated in the extended nuclear statistical equilibrium model. The EOS table is generated for a wide range of values of three parameters—baryon density (10⁻¹² to ∼1 fm⁻³), positive charge fraction (0.01–0.60), and temperature (0.1–158.48 MeV).

Periodic outbursts are observed in several changing-look (CL) active galactic nuclei (AGNs). Sniegowska et al. suggested a model to explain the repeating CL in these AGNs, where the periodic outbursts are triggered in a narrow unstable zone between an inner advection-dominated accretion flow and outer thin disk. In this work, we intend to investigate the effects of large-scale magnetic fields on the limit cycle behaviors of CL AGNs. The winds driven by magnetic fields can significantly change the structure of thin disk by taking away the angular momentum and energy of the disk. It is found that the period of outburst in repeating CL AGNs can be substantially reduced by the magnetic fields. Conversely, if we keep the period unchanged, the outburst intensity can be raised by several times. These results can help to explain the observational properties of multiple CL AGNs. Besides the magnetic fields, the effects of transition radius ${R}_{\mathrm{tr}}$, the width of the transition zone ΔR, and the Shakura–Sunyaev parameter α are also explored in this work.

A range of cosmological observations demonstrate an accelerated expansion of the universe, and the most likely explanation of this phenomenon is a cosmological constant. Given the importance of understanding the underlying physics, it is relevant to investigate alternative models. This article uses numerical simulations to test the consistency of one such alternative model. Specifically, this model has no cosmological constant; instead, the dark matter particles have an extra force proportional to the velocity squared, somewhat reminiscent of the magnetic force in electrodynamics. The constant strength of the force is the only free parameter. Because bottom-up structure formation creates cosmological structures whose internal velocity dispersions increase in time, this model may mimic the temporal evolution of the effect from a cosmological constant. It is shown that models with force linearly proportional to internal velocities, or models proportional to velocity to power 3 or more, cannot mimic the accelerated expansion induced by a cosmological constant. However, models proportional to velocity squared are still consistent with the temporal evolution of a universe with a cosmological model.

Based on galactic cosmic ray (GCR) and plasma observations from the ACE spacecraft, in this work, we analyze the relation between the GCR counts and the solar wind parameters during two recent two solar minima (for the years 2007.0–2009.0, and 2016.5–2018.5) by means of the superposed epoch analysis (SEA) method. The results indicate that GCRs are strongly modulated by the co-rotating interaction regions (CIRs) in the solar wind, and that the occurrences of stream interfaces (SIs) between fast and slow solar wind are correlated with a depression in GCR counts. The so-called "snow plow" effect of GCR variation prior to SI crossing appears during the first solar minimum, and the GCR counts decrease after the crossing, corresponding to a sudden drop in the diffusion coefficient at the SIs. The gradient of GCR counts shows that the transport efficiency of GCRs is low (high), relative to slow (fast) solar wind. However, during the second solar minimum, we see a completely opposite scenario; the "snow plow" effect is not observed, and GCR transport becomes faster in slow solar wind, and slower in fast solar wind. In addition, heliospheric current-sheet crossings also correlate with GCR counts. Particles drift along the current sheet, then accumulate in a pileup structure, where diffusion and drift effects may be balanced. It is found that the drift effect rivals the diffusion and convection on the GCR transport at 1 au during the two solar minima.

Blazars are potential sources of cosmic-ray acceleration up to ultrahigh energies (E ≳ 10¹⁸ eV). For an efficient cosmic-ray injection from blazars, pγ collisions with extragalactic background light (EBL) and cosmic microwave background (CMB) can produce neutrino spectra with peaks near to PeV and EeV energies, respectively. In this work, we analyze the contribution of these neutrinos to the diffuse background measured by the IceCube neutrino observatory. The fraction of neutrino luminosity originating from individual redshift ranges is calculated using the distribution of BL Lacs and FSRQs provided in the Fermi-LAT 4LAC catalog. Furthermore, we use a luminosity-dependent density evolution to find the neutrino flux of unresolved blazars. The results obtained in our model indicate that as much as ≈10% of the flux upper bound at a few PeV energies can arise from cosmic-ray interactions with EBL. The same interactions will also produce secondary electrons and photons, initiating electromagnetic cascades. The resultant photon spectrum is limited by the isotropic diffuse γ-ray flux measured between 100 MeV and 820 GeV. The latter, together with the observed cosmic-ray flux at E > 10^16.5 eV, can constrain the baryonic loading factor, depending on the maximum cosmic-ray acceleration energy.

Periodic quasars have been suggested to host supermassive binary black holes (BBHs) in their centers, and their optical/UV periodicities are interpreted as caused by either the Doppler-boosting (DB) effect of continuum emission from the disk around the secondary black hole (BH) or intrinsic accretion rate variation. However, no other definitive evidence has been found to confirm such a BBH interpretation(s). In this paper, we investigate the responses of broad emission lines (BELs) to the continuum variations for these quasars under two BBH scenarios and check whether they can be distinguished from each other and from that of a single BH system. We assume a simple circumbinary broad-line region (BLR) model, compatible with BLR size estimates, with a standard Γ distribution of BLR clouds. We find that BELs may change significantly and periodically under the BBH scenarios due to (1) the position variation of the secondary BH and (2) the DB effect, if significant, and/or intrinsic variation, which is significantly different from the case of a single BH system. For the two BBH scenarios, the responses of BELs to (apparent) continuum variations, caused by the DB effect or intrinsic rate variation, are also significantly different from each other, mainly because the DB effect has a preferred direction along the direction of motion of the secondary BH, while that due to intrinsic variation does not. Such differences in the responses of BELs from different scenarios may offer a robust way to distinguish different interpretations of periodic quasars and to identify BBHs, if any, in these systems.

Although blue horizontal branch (BHB) stars are commonly used to trace halo substructure, the stars bluer than (g − r) < −0.3 are ignored owing to the difficulty in determining their absolute magnitudes. The blue extension of the horizontal branch (HBX) includes BHB tail stars and extreme horizontal branch (EHB) stars. We present a method for identifying HBX stars in the field, using spectra and photometry from the Sloan Digital Sky Survey Data Release 14 (SDSS DR14). We derive an estimate for the absolute magnitudes of BHB tail and EHB stars as a function of color and use this relationship to calculate distances. We identify an overdensity of HBX stars that appears to trace the northern end of the Hercules-Aquila Cloud. We identify three stars that are likely part of a tidal stream, but this is not enough stars to explain the observed overdensity. Combining SDSS data with Gaia DR2 proper motions allows us to show that the majority of the HBX stars in the overdensity are on high-eccentricity orbits similar to those in the Virgo Radial Merger/Gaia–Enceladus/Gaia Sausage structure and that the overdensity of high-eccentricity orbits extends all the way to the Virgo Overdensity. We use stellar kinematics to separate the HBX stars into disk stars and halo stars. The halo stars are primarily on highly eccentric (radial) orbits. The fraction of HBX stars that are EHBs is highest in the disk population and lowest in the low-eccentricity halo stars.

We present a systematic X-ray and multiwavelength study of a sample of 47 active galactic nuclei (AGNs) with reverberation mapping measurements. This sample includes 21 super-Eddington accreting AGNs and 26 sub-Eddington accreting AGNs. Using high-state observations with simultaneous X-ray and UV/optical measurements, we investigate whether super-Eddington accreting AGNs exhibit different accretion disk–corona connections compared to sub-Eddington accreting AGNs. We find tight correlations between the X-ray-to-UV/optical spectral slope parameter (α_OX) and the monochromatic luminosity at 2500 Å (L_2500Å) for both the super- and sub-Eddington subsamples. The best-fit α_OX–L_2500Å relations are consistent overall, indicating that super-Eddington accreting AGNs are not particularly X-ray weak in general compared to sub-Eddington accreting AGNs. We find dependences of α_OX on both the Eddington ratio (L_Bol/L_Edd) and black hole mass (M_BH) parameters for our full sample. A multivariate linear regression analysis yields ${\alpha }_{\mathrm{OX}}=-0.13\mathrm{log}({L}_{\mathrm{Bol}}/{L}_{\mathrm{Edd}})-0.10\mathrm{log}{M}_{\mathrm{BH}}-0.69$, with a scatter similar to that of the α_OX–L_2500Å relation. The hard (rest-frame >2 keV) X-ray photon index (Γ) is strongly correlated with L_Bol/L_Edd for the full sample and the super-Eddington subsample, but these two parameters are not significantly correlated for the sub-Eddington subsample. A fraction of super-Eddington accreting AGNs show strong X-ray variability, probably due to small-scale gas absorption, and we highlight the importance of employing high-state (intrinsic) X-ray radiation to study the accretion disk–corona connections in AGNs.

We present the largest currently existing subarcsecond 3–5 μm atlas of 119 local (z < 0.3) active galactic nuclei (AGNs). This atlas includes AGNs of five subtypes: 22 are Seyfert 1; five are intermediate Seyferts; 46 are Seyfert 2; 26 are low-ionization nuclear emission regions; and 20 are composites/starbursts. Each active galactic nucleus was observed with the Very Large Telescope Infrared Spectrometer and Array Camera (ISAAC) in the L and/or M bands between 2000 and 2013. We detected at 3σ confidence 92 sources in the L band and 83 sources in the M band. We separated the flux into unresolved nuclear flux and resolved the flux through two-Gaussian fitting. We report the nuclear flux, extended flux, apparent size, and position angle of each source, giving 3σ upper limits for sources that are undetected. Using Wide-field Infrared Survey Explorer (WISE) W1- and W2-band photometry we derived relations predicting the nuclear L and M fluxes for Sy1 and Sy2 AGNs based on their W1–W2 color and WISE fluxes. Lastly, we compare the measured mid-infrared colors to those predicted by dusty torus models SKIRTOR, CLUMPY, CAT3D, and CAT3D-WIND, finding the best agreement with the latter. We find that models including polar winds best reproduce the 3–5 μm colors, indicating that it is an important component of dusty torus models. We found that several AGNs are bluer than models predict. We discuss several explanations for this and find that it is most plausibly stellar light contamination within the ISAAC L-band nuclear fluxes.

The Frontier Fields project is an observational campaign targeting six galaxy clusters, with the intention of using the magnification provided by gravitational lensing to study galaxies that are extremely faint or distant. We used the Karl G. Jansky Very Large Array (VLA) at 3 and 6 GHz to observe three Frontier Fields: MACS J0416.1−2403 (z = 0.396), MACS J0717.5+3745 (z = 0.545), and MACS J1149.5+2223 (z = 0.543). The images reach noise levels of ∼1 μJy beam⁻¹ with subarcsecond resolution (∼2.5 kpc at z = 3), providing a high-resolution view of high-z star-forming galaxies that is unbiased by dust obscuration. We generate dual-frequency continuum images at two different resolutions per band, per cluster, and derive catalogs totaling 1966 compact radio sources. Components within the areas of Hubble Space Telescope and Subaru observations are cross-matched, providing host galaxy identifications for 1296 of them. We detect 13 moderately lensed (2.1 < μ < 6.5) sources, one of which has a demagnified peak brightness of 0.9 μJy beam⁻¹, making it a candidate for the faintest radio source ever detected. There are 66 radio sources exhibiting complex morphologies, and 58 of these have host galaxy identifications. We reveal that MACS J1149.5+2223 is not a cluster with a double relic, as the western candidate relic is resolved as a double-lobed radio galaxy associated with a foreground elliptical at z = 0.24. The VLA Frontier Fields project is a public legacy survey. The image and catalog products from this work are freely available.

To investigate the growth history of galaxies, we measure the rest-frame radio, ultraviolet (UV), and optical sizes of 98 radio-selected, star-forming galaxies (SFGs) distributed over 0.3 ≲ z ≲ 3 with a median stellar mass of $\mathrm{log}({M}_{\star }/{M}_{\odot })\approx 10.4$. We compare the size of galaxy stellar disks, traced by rest-frame optical emission, relative to the overall extent of star formation activity that is traced by radio continuum emission. Galaxies in our sample are identified in three Hubble Frontier Fields: MACS J0416.1−2403, MACS J0717.5+3745, and MACS J1149.5+2223. Radio continuum sizes are derived from 3 and 6 GHz radio images (≲06 resolution, ≈0.9 μJy beam⁻¹ noise level) from the Karl G. Jansky Very Large Array. Rest-frame UV and optical sizes are derived using observations from the Hubble Space Telescope and the Advanced Camera for Surveys and Wide Field Camera 3 instruments. We find no clear dependence between the 3 GHz radio size and stellar mass of SFGs, which contrasts with the positive correlation between the UV/optical size and stellar mass of galaxies. Focusing on SFGs with $\mathrm{log}({M}_{\star }/{M}_{\odot })\gt 10$, we find that the radio/UV/optical emission tends to be more compact in galaxies with high star formation rates (≳100 M_⊙ yr⁻¹), suggesting that a central, compact starburst (and/or an active galactic nucleus) resides in the most luminous galaxies of our sample. We also find that the physical radio/UV/optical size of radio-selected SFGs with log(M_⋆/M_⊙) > 10 increases by a factor of 1.5–2 from z ≈ 3 to z ≈ 0.3, yet the radio emission remains two to three times more compact than that from the UV/optical. These findings indicate that these massive, radio-selected SFGs at 0.3 ≲ z ≲ 3 tend to harbor centrally enhanced star formation activity relative to their outer disks.

Ions that are reflected at the shock front and escape back into the upstream region can play the role of ions that start to be accelerated by a diffusive shock acceleration mechanism. Backstreaming ions have been shown to be generated from a superthermal tail of the solar wind at sufficiently high upstream temperatures. The number of such ions was found to be low and they were not found at shock angles exceeding 50°. The mechanism of production is multiple reflection when an ion changes the direction of motion inside the ramp for the first time, due to the cross-shock potential. Since pickup ions (PUIs) constitute a strongly superthermal population of protons a substantially stronger production of backstreaming PUIs can be expected. We study the reflection of PUIs in a planar stationary shock front using test particle analysis. The used model is inspired by the observed profile of the termination shock. The influence of magnetic compression, the shock angle, and the overshoot are analyzed. It is found that generation of backstreaming PUIs in this shock is substantially more efficient than the generation of backstreaming protons from thermal solar wind. The fraction of backstreaming PUIs rapidly increases with the increase of magnetic compression and the decrease of the shock angle. Overshoot enhances production of backstreaming PUIs and allows it for larger shock angles. No backstreaming ions have been found for shock angles larger than 60°. The results of the test particle analysis are supported by full-particle simulations.

Narrowband spikes have been observed in solar flares for several decades. However, their exact origin is still discussed. To contribute to understanding of these spikes, we analyze the narrowband spikes observed in the 800–2000 MHz range during the impulsive phase of the 2013 November 7 flare. In the radio spectrum, the spikes started with typical broadband clouds of spikes, and then their distribution in frequencies changed into unique, very narrow bands having noninteger frequency ratios. We successfully fitted frequencies of these narrow spike bands by those, calculating dispersion branches and growth rates of the Bernstein modes. For comparison, we also analyzed the model where the narrow bands of spikes are generated at the upper-hybrid frequencies. Using both models, we estimated the plasma density and magnetic field in spike sources. Then, the models are discussed, and arguments in favor of the model with the Bernstein modes are presented. Analyzing frequency profiles of this spike event by the Fourier method, we found the power-law spectra with the power-law indices varying in the −0.8 to −2.75 interval. Because at some times this power-law index was close to the Kolmogorov spectral index (−5/3), we propose that the spikes are generated through the Bernstein modes in turbulent plasma reconnection outflows or directly in the turbulent magnetic reconnection of solar flares.

Imaging surveys of CO and other molecular transition lines are fundamental to measuring the large-scale distribution of molecular gas in the Milky Way. Due to finite angular resolution and sensitivity, however, observational effects are inevitable in the surveys, but few studies are available on the extent of uncertainties involved. The purpose of this work is to investigate the dependence of observations on angular resolution (beam sizes), sensitivity (noise levels), distances, and molecular tracers. To this end, we use high-quality CO images of a large-scale region (258 < l < 497 and ∣b∣ < 5°) mapped by the Milky Way Imaging Scroll Painting (MWISP) survey as a benchmark to simulate observations with larger beam sizes and higher noise levels, deriving corresponding beam filling and sensitivity clip factors. The sensitivity clip factor is defined to be the completeness of observed flux. Taking the entire image as a whole object, we found that ¹²CO has the largest beam filling and sensitivity clip factors and C¹⁸O has the lowest. For molecular cloud samples extracted from images, the beam filling factor can be described by a characteristic size, l_1/4 = 0.762 (in beam size), at which the beam filling factor is approximately 1/4. The sensitivity clip factor shows a similar relationship but is more correlated with the mean voxel signal-to-noise ratio of molecular clouds. This result may serve as a practical reference on beam filling and sensitivity clip factors in further analyses of the MWISP data and other observations.

The magnetic activity of late-type stars is correlated with their rotation rates. Up to a certain limit, stars with smaller Rossby numbers, defined as the rotation period divided by the convective turnover time, have higher activity. A more detailed look at this rotation–activity relation reveals that, rather than being a simple power-law relation, the activity scaling has a shallower slope for the low-Rossby stars than for the high-Rossby ones. We find that, for the chromospheric Ca II H&K activity, this scaling relation is well modeled by a broken two-piece power law. Furthermore, the knee point of the relation coincides with the axisymmetry to nonaxisymmetry transition seen in both the spot activity and surface magnetic field configuration of active stars. We interpret this knee point as a dynamo transition between dominating axi- and nonaxisymmetric dynamo regimes with a different dependence on rotation and discuss this hypothesis in the light of current numerical dynamo models.

We present a detailed study of KIC 2306740, an eccentric double-lined eclipsing binary system. Kepler satellite data were combined with spectroscopic data obtained with the 4.2 m William Herschel Telescope (WHT). This allowed us to determine precise orbital and physical parameters of this relatively long period (P = 103) and slightly eccentric (e = 0.3) binary system. The physical parameters have been determined to be M₁ = 1.194 ± 0.008 M_⊙, M₂ = 1.078 ± 0.007 M_⊙, R₁ = 1.682 ± 0.004 R_⊙, R₂ = 1.226 ± 0.005 R_⊙, L₁ = 2.8 ± 0.4 L_⊙, L₂ = 1.8 ± 0.2 L_⊙, and orbital separation a = 26.20 ± 0.04 R_⊙ through simultaneous solutions of the Kepler light curves and WHT radial velocity data. Binarity effects were extracted from the light curve in order to study intrinsic variations in the residuals. Five significant and more than 100 combination frequencies were detected. We modeled the binary system assuming nonconservative evolution models with the Cambridge stars (twin) code, and we show the evolutionary tracks of the components in the $\mathrm{log}L\mbox{--}\mathrm{log}T$ plane, the $\mathrm{log}R\mbox{--}\mathrm{log}M$ plane, and the $\mathrm{log}P\mbox{--}\mathrm{age}$ plane for both spin and orbital periods together with eccentricity e and $\mathrm{log}{R}_{1}$. The model of the nonconservative processes in the code led the system to evolve to the observed system parameters in roughly 5.1 Gyr.

We present the results of a single-dish survey toward 95 very low luminosity objects (VeLLOs) in optically thick (HCN 1−0) and thin (N₂H⁺ 1−0) lines performed for the purpose of understanding the physical processes of inward motions in the envelopes of the VeLLOs and characterizing their true nature. The normalized velocity differences ($\delta {V}_{\mathrm{HCN}}$) between the peak velocities of the two lines were derived for 41 VeLLOs detected in both lines. The δV distribution of these VeLLOs is found to be significantly skewed to the blue, indicating the dominance of infalling motions in their envelopes. The infall speeds were derived for 15 infall candidates by using the HILL5 radiative transfer model. The speeds were in the range of 0.03−0.3 km s⁻¹, with a median value of 0.16 km s⁻¹, consistent with the gravitational freefall speeds from pressure-free envelopes. The mass infall rates calculated from the infall speeds are mostly of the order of 10⁻⁶M_⊙ yr⁻¹, with a median value of (3.4 ± 1.5) × 10⁻⁶M_⊙ yr⁻¹. These are found to be also consistent with the values predicted with the inside-out collapse model and show a fairly good correlation with the internal luminosities of the VeLLOs. This again indicates that the infall motions observed toward the VeLLOs are likely to be due to the gravitational infall motions in their envelopes. Our study suggests that most of the VeLLOs are potentially faint protostars, while two of the VeLLOs could possibly be proto−brown dwarf candidates.

Active regions in the inner solar corona, when observed in X-ray emission, consist of bright, hot loops surrounded by unstructured clouds. The emission from the clouds extends to a height of ≈4–5 × 10⁴ km at temperatures of ≈2–3 MK. These "hot clouds" are variable, but persist for many days and do not appear to connect directly to the active region streamers or other large-scale structures observed higher in the corona. We present an observational analysis of these diffuse structures to establish basic plasma parameters such as magnetic field strength, particle density, and temperature. The values of β, the ratio of the plasma pressure to the magnetic field pressure, were found to be generally less than unity, though often approaching unity in the upper portions of the active region, where the hot clouds are located. The magnetic field may therefore only partially confine these regions and inhibit flare-like instabilities that could otherwise be driven by gradients of plasma pressure and current density.

Similarities in the chemical composition of two of the closest Milky Way satellites, namely, the Large Magellanic Cloud (LMC) and the Sagittarius (Sgr) dwarf galaxy, have been proposed in the literature, suggesting similar chemical enrichment histories between the two galaxies. This proposition, however, rests on different abundance analyses, which likely introduce various systematics that hamper a fair comparison among the different data sets. In order to bypass this issue (and highlight real similarities and differences between their abundance patterns), we present a homogeneous chemical analysis of 30 giant stars in the LMC, 14 giant stars in Sgr, and 14 giants in the Milky Way, based on high-resolution spectra taken with the spectrograph UVES-FLAMES. The LMC and Sgr stars, in the considered metallicity range ([Fe/H] > −1.1 dex), show very similar abundance ratios for almost all the elements, with differences only in the heavy s-process elements Ba, La, and Nd, suggesting a different contribution by asymptotic giant branch stars. On the other hand, the two galaxies have chemical patterns clearly different from those measured in the Galactic stars, especially for the elements produced by massive stars. This finding suggests that the massive stars contributed less to the chemical enrichment of these galaxies with respect to the Milky Way. The derived abundances support similar chemical enrichment histories for the LMC and Sgr.

We present an analysis of UV spectra of 13 quasars believed to belong to extreme Population A (xA) quasars, aimed at the estimation of the chemical abundances of the broad-line-emitting gas. Metallicity estimates for the broad-line-emitting gas of quasars are subject to a number of caveats; xA sources with the strongest Fe ii emission offer several advantages with respect to the quasar general population, as their optical and UV emission lines can be interpreted as the sum of a low-ionization component roughly at quasar rest frame (from virialized gas), plus a blueshifted excess (a disk wind), in different physical conditions. Capitalizing on these results, we analyze the component at rest frame and the blueshifted one, exploiting the dependence of several intensity line ratios on metallicity Z. We find that the validity of intensity line ratios as metallicity indicators depends on the physical conditions. We apply the measured diagnostic ratios to estimate the physical properties of sources such as density, ionization, and metallicity of the gas. Our results confirm that the two regions (the low-ionization component and the blueshifted excess) of different dynamical conditions also show different physical conditions and suggest metallicity values that are high, and probably the highest along the quasar main sequence, with Z ∼ 20−50 Z_⊙, if the solar abundance ratios can be assumed constant. We found some evidence of an overabundance of aluminum with respect to carbon, possibly due to selective enrichment of the broad-line-emitting gas by supernova ejecta.

The detailed observations of GW170817 proved for the first time directly that neutron star mergers are a major production site of heavy elements. The observations could be fit by a number of simulations that qualitatively agree, but can quantitatively differ (e.g., in total r-process mass) by an order of magnitude. We categorize kilonova ejecta into several typical morphologies motivated by numerical simulations, and apply a radiative transfer Monte Carlo code to study how the geometric distribution of the ejecta shapes the emitted radiation. We find major impacts on both spectra and light curves. The peak bolometric luminosity can vary by two orders of magnitude and the timing of its peak by a factor of five. These findings provide the crucial implication that the ejecta masses inferred from observations around the peak brightness are uncertain by at least an order of magnitude. Mixed two-component models with lanthanide-rich ejecta are particularly sensitive to geometric distribution. A subset of mixed models shows very strong viewing angle dependence due to lanthanide "curtaining," which persists even if the relative mass of lanthanide-rich component is small. The angular dependence is weak in the rest of our models, but different geometric combinations of the two components lead to a highly diverse set of light curves. We identify geometry-dependent P Cygni features in late spectra that directly map out strong lines in the simulated opacity of neodymium, which can help to constrain the ejecta geometry and to directly probe the r-process abundances.

Several massive (M_* > 10⁸M_⊙), high-redshift (z = 8–10) galaxies have recently been discovered to contain stars with ages of several hundred million years, pushing the onset of star formation in these galaxies back to z ∼ 15. The very existence of stars formed so early may serve as a test for cosmological models with suppressed small-scale power (and, hence, late formation of cosmic structure). We explore the ages of the oldest stars in numerical simulations from the Cosmic Reionization On Computers project with cold dark matter (CDM) and two warm dark matter (WDM) cosmologies with 3 and 6 keV particles. There are statistically significant differences of ∼5 Myr between average stellar ages of massive galaxies in CDM and 3 keV WDM, while CDM and 6 keV WDM are statistically indistinguishable. Even this 5 Myr difference, however, is much less than current observational uncertainties on the stellar population properties of high-redshift galaxies. The age distributions of all galaxies in all cosmologies fail to produce a substantial Balmer break, although uncertainties in dust attenuation are a potentially significant factor. Finally, we assess the convergence of our simulation predictions and find that the systematic uncertainties on individual galaxy properties are comparable to the differences between cosmologies, suggesting these differences may not be numerically robust.

Masses of classical Cepheids of 3–11 M_⊙ are predicted by theory but those measured clump between 3.6–5 M_⊙. As a result, their mass–luminosity relation is poorly constrained, impeding our understanding of basic stellar physics and the Leavitt Law. All Cepheid masses come from the analysis of 11 binary systems, including only five that are double lined and well suited for accurate dynamical mass determination. We present a project to analyze a new, numerous group of Cepheids in double-lined binary (SB2) systems to provide mass determinations in a wide mass interval and study their evolution. We analyze a sample of 41 candidate binary LMC Cepheids spread along the P–L relation, which are likely accompanied by luminous red giants, and present indirect and direct indicators of their binarity. In a spectroscopic study of a subsample of 18 brightest candidates, for 16 we detected lines of two components in the spectra, already quadrupling the number of Cepheids in SB2 systems. Observations of the whole sample may thus lead to quadrupling all the Cepheid mass estimates available now. For the majority of our candidates, erratic intrinsic period changes dominate over the light-travel-time effect due to binarity. However, the latter may explain the periodic phase modulation for four Cepheids. Our project paves the way for future accurate dynamical mass determinations of Cepheids in the LMC, Milky Way, and other galaxies, which will potentially increase the number of known Cepheid masses even 10-fold, hugely improving our knowledge about these important stars.

With an effective temperature of ≃200,000 K, KPD 0005+5106 is one of the hottest white dwarfs (WDs). ROSAT unexpectedly detected "hard" (∼1 keV) X-rays from this apparently single WD. We have obtained Chandra observations that confirm the spatial coincidence of this hard X-ray source with KPD 0005+5106. We have also obtained XMM-Newton observations of KPD 0005+5106, as well as PG 1159−035 and WD 0121−756, which are also apparently single and whose hard X-rays were detected by ROSAT at 3σ–4σ levels. The XMM-Newton spectra of the three WDs show remarkably similar shapes that can be fitted by models including a blackbody component for the stellar photospheric emission, a thermal plasma emission component, and a power-law component. Their X-ray luminosities in the 0.6–3.0 keV band range from 4 × 10²⁹ to 4 × 10³⁰ erg s⁻¹. The XMM-Newton EPIC-pn soft-band (0.3–0.5 keV) light curve of KPD 0005+5106 is essentially constant, but the hard-band (0.6–3.0 keV) light curve shows periodic variations. An analysis of the generalized Lomb–Scargle periodograms for the XMM-Newton and Chandra hard-band light curves finds a convincing modulation (false-alarm probability of 0.41%) with a period of 4.7 ± 0.3 hr. Assuming that this period corresponds to a binary orbital period, the Roche radii of three viable types of companion have been calculated: M9V star, T brown dwarf, and Jupiter-like planet. Only the planet has a size larger than its Roche radius, although the M9V star and T brown dwarf may be heated by the WD and inflate past the Roche radius. Thus, all three types of companion may be donors to fuel accretion-powered hard X-ray emission.

The unprecedented sky coverage and observing cadence of the All-Sky Automated Survey for SuperNovae (ASAS-SN) has resulted in the discovery and continued monitoring of a large sample of Galactic transients. The vast majority of these are accretion-powered dwarf nova outbursts in cataclysmic variable systems, but a small subset are thermonuclear-powered classical novae. Despite improved monitoring of the Galaxy for novae from ASAS-SN and other surveys, the observed Galactic nova rate is still lower than predictions. One way classical novae could be missed is if they are confused with the much larger population of dwarf novae. Here, we examine the properties of 1617 dwarf nova outbursts detected by ASAS-SN and compare them to classical novae. We find that the mean classical nova brightens by ∼11 mag during outburst, while the mean dwarf nova brightens by only ∼5 mag, with the outburst amplitude distributions overlapping by roughly 15%. For the first time, we show that the amplitude of an outburst and the time it takes to decline by two magnitudes from maximum are positively correlated for dwarf nova outbursts. For classical novae, we find that these quantities are negatively correlated, but only weakly, compared to the strong anticorrelation of these quantities found in some previous work. We show that, even if located at large distances, only a small number of putative dwarf novae could be misclassified as classical novae, suggesting that there is minimal confusion between these populations. Future spectroscopic follow-up of these candidates can show whether any are indeed classical novae.

The zero point of the reddening toward the Large Magellanic Cloud (LMC) has been the subject of some dispute. Its uncertainty propagates as a systematic error for methods that measure the extragalactic distance scale through knowledge of the absolute extinction of LMC stars. In an effort to resolve this issue, we used three different methods to calibrate the most widely used metric to predict LMC extinction, the intrinsic color of the red clump, (V − I)_RC,0, for the inner ∼3° of that galaxy. The first approach was to empirically calibrate the color zero points of the BaSTI isochrones over a wide metallicity range of Δ[Fe/H] ≈ 1.10 using measurements of red clump stars in 47 Tuc, the solar neighborhood, and NGC 6791. From these efforts, we also measure these properties of the solar neighborhood red clump, (V − I, G_BP − K_s, G − K_s, G_RP − K_s, J − K_s, H − K_s, M_I, M_Ks)_RC,0 = (1.02, 2.75, 2.18, 1.52, 0.64, 0.15, −0.23, −1.63). The second and third methods were to compare the observed colors of the red clump to those of Cepheids and RR Lyrae in the LMC. With these three methods, we estimated the intrinsic color of the red clump of the LMC to be (V − I)_RC,0,LMC = {≈0.93, 0.91 ± 0.02, 0.89 ± 0.02}, respectively, and similarly, using the first and third methods, we estimated (V − I)_RC,0,SMC = {≈0.85, 0.84 ± 0.02}, respectively, for the Small Magellanic Cloud. We estimate the luminosities to be M_I,RC,LMC = −0.26 and M_I,RC,SMC = −0.37. We show that this has important implications for recent calibrations of the tip of the red giant branch in the Magellanic Clouds used to measure H₀.

The complex interplay of magnetohydrodynamics, gravity, and supersonic turbulence in the interstellar medium (ISM) introduces a non-Gaussian structure that can complicate a comparison between theory and observation. In this paper, we show that the wavelet scattering transform (WST), in combination with linear discriminant analysis (LDA), is sensitive to non-Gaussian structure in 2D ISM dust maps. WST-LDA classifies magnetohydrodynamic (MHD) turbulence simulations with up to a 97% true positive rate in our testbed of 8 simulations with varying sonic and Alfvénic Mach numbers. We present a side-by-side comparison with two other methods for non-Gaussian characterization, the reduced wavelet scattering transform (RWST) and the three-point correlation function (3PCF). We also demonstrate the 3D-WST-LDA, and apply it to the classification of density fields in position–position–velocity (PPV) space, where density correlations can be studied using velocity coherence as a proxy. WST-LDA is robust to common observational artifacts, such as striping and missing data, while also being sensitive enough to extract the net magnetic field direction for sub-Alfvénic turbulent density fields. We include a brief analysis of the effect of point-spread functions and image pixelization on 2D-WST-LDA applied to density fields, which informs the future goal of applying WST-LDA to 2D or 3D all-sky dust maps to extract hydrodynamic parameters of interest.

A common feature of electromagnetic emission from solar flares is the presence of intensity pulsations that vary as a function of time. Known as quasi-periodic pulsations (QPPs), these variations in flux appear to include periodic components and characteristic timescales. Here, we analyze a GOES M3.7 class flare exhibiting pronounced QPPs across a broad band of wavelengths using imaging and time series analysis. We identify QPPs in the time series of X-ray, low-frequency radio, and extreme ultraviolet (EUV) wavelengths using wavelet analysis, and localize the region of the flare site from which the QPPs originate via X-ray and EUV imaging. It was found that the pulsations within the 171 Å, 1600 Å, soft X-ray, and hard X-ray light curves yielded similar periods of ${122}_{-22}^{+26}$ s, ${131}_{-27}^{+36}$ s, ${123}_{-26}^{+11}$ s, and ${137}_{-56}^{+49}$ s, respectively, indicating a common progenitor. The low-frequency radio emission at 2.5 MHz contained a longer period of ∼231 s. Imaging analysis indicates that the location of the X-ray and EUV pulsations originates from a hard X-ray footpoint linked to a system of nearby open magnetic field lines. Our results suggest that intermittent particle acceleration, likely due to "bursty" magnetic reconnection, is responsible for the QPPs. The precipitating electrons accelerated toward the chromosphere produce the X-ray and EUV pulsations, while the escaping electrons result in low-frequency radio pulses in the form of type III radio bursts. The modulation of the reconnection process, resulting in episodic particle acceleration, explains the presence of these QPPs across the entire spatial range of flaring emission.

The star formation activity of the host galaxies of active galactic nuclei provides valuable insights into the complex interconnections between black hole growth and galaxy evolution. A major obstacle arises from the difficulty of estimating accurate star formation rates (SFRs) in the presence of a strong active galactic nucleus. Analyzing the 1–500 μm spectral energy distributions and high-resolution mid-infrared spectra of low-redshift (z < 0.5) Palomar–Green quasars with bolometric luminosity of ∼10^44.5–10^47.5 erg s⁻¹, we find, from comparison with an independent SFR indicator based on [Ne II] 12.81 μm and [Ne III] 15.56 μm, that the torus-subtracted, total infrared (8–1000 μm) emission yields robust SFRs in the range of ∼1–250 M_⊙ yr⁻¹. Combined with available stellar mass estimates, the vast majority (∼75%–90%) of the quasars lie on or above the main sequence of local star-forming galaxies, including a significant fraction (∼50%–70%) that would qualify as starburst systems. This is further supported by the high star formation efficiencies derived from the gas content inferred from the dust masses. Inspection of high-resolution Hubble Space Telescope images reveals a wide diversity of morphological types, including a number of starbursting hosts that have not experienced significant recent dynamical perturbations. The origin of the high star formation efficiency is unknown.

We present the discovery that ASASSN-14ko is a periodically flaring active galactic nucleus at the center of the galaxy ESO 253-G003. At the time of its discovery by the All-Sky Automated Survey for Supernovae (ASAS-SN), it was classified as a supernova close to the nucleus. The subsequent 6 yr of V- and g-band ASAS-SN observations revealed that ASASSN-14ko has nuclear flares occurring at regular intervals. The 17 observed outbursts show evidence of a decreasing period over time, with a mean period of P₀ = 114.2 ± 0.4 days and a period derivative of $\dot{P}=-0.0017\pm 0.0003$. The most recent outburst in 2020 May, which took place as predicted, exhibited spectroscopic changes during the rise and had a UV bright, blackbody spectral energy distribution similar to tidal disruption events (TDEs). The X-ray flux decreased by a factor of 4 at the beginning of the outburst and then returned to its quiescent flux after ∼8 days. The Transiting Exoplanet Survey Satellite observed an outburst during Sectors 4–6, revealing a rise time of 5.60 ± 0.05 days in the optical and a decline that is best fit with an exponential model. We discuss several possible scenarios to explain ASASSN-14ko's periodic outbursts, but currently favor a repeated partial TDE. The next outbursts should peak in the optical on UT 2020 September 7.4±1.1 and UT 2020 December 26.5±1.4.

Observations of the γ-ray emission around star clusters, isolated supernova remnants, and pulsar wind nebulae indicate that the cosmic-ray (CR) diffusion coefficient near acceleration sites can be suppressed by a large factor compared to the Galaxy average. We explore the effects of such local suppression of CR diffusion on galaxy evolution using simulations of isolated disk galaxies with regular and high gas fractions. Our results show that while CR propagation with constant diffusivity can make gaseous disks more stable by increasing the midplane pressure, large-scale CR pressure gradients cannot prevent local fragmentation when the disk is unstable. In contrast, when CR diffusivity is suppressed in star-forming regions, the accumulation of CRs in these regions results in strong local pressure gradients that prevent the formation of massive gaseous clumps. As a result, the distribution of dense gas and star formation changes qualitatively: a globally unstable gaseous disk does not violently fragment into massive star-forming clumps but maintains a regular grand-design spiral structure. This effect regulates star formation and disk structure and is qualitatively different from and complementary to the global role of CRs in vertical hydrostatic support of the gaseous disk and in driving galactic winds.

We have examined the star formation history (SFH) of Andromeda VII (And VII), the brightest and most massive dwarf spheroidal (dSph) satellite of the Andromeda galaxy (M31). Although M31 is surrounded by several dSph companions with old stellar populations and low metallicity, it has a metal-rich stellar halo with an age of 6–8 Gyr. This indicates that any evolutionary association between the stellar halo of M31 and its dSph system is frail. Therefore, the question is whether And VII (a high-metallicity dSph located ∼220 kpc from M31) can be associated with M31's young, metal-rich halo. Here we perform the first reconstruction of the SFH of And VII employing long-period variable (LPV) stars. As the most evolved asymptotic giant branch and red supergiant stars, the birth mass of LPVs can be determined by connecting their near-infrared photometry to theoretical evolutionary tracks. We found 55 LPV candidates within two half-light radii, using multiepoch imaging with the Isaac Newton Telescope in the i and V bands. Based on their birth mass function, the star formation rate (SFR) of And VII was obtained as a function of cosmic time. The main epoch of star formation occurred ≃ 6.2 Gyr ago with an SFR of 0.006 ± 0.002 M_⊙ yr⁻¹. Over the past 6 Gyr, we find slow star formation, which continued until 500 Myr ago with an SFR ∼ 0.0005 ± 0.0002 M_⊙ yr⁻¹. We determined And VII's stellar mass M = (13.3 ± 5.3) × 10⁶M_⊙ within a half-light radius ${r}_{\tfrac{1}{2}}=3\buildrel{\,\prime}\over{.} 8\pm 0\buildrel{\,\prime}\over{.} 3$ and metallicity Z = 0.0007, and we also derived its distance modulus of μ = 24.38 mag.

Shock breakout (SBO), the first expected electromagnetic signature of a supernova (SN), can be an important probe of the progenitors of these explosions. Unfortunately, SBO is difficult to capture with current surveys due to its brief timescale (≲1 hr). However, SBO may be lengthened when dense circumstellar material (CSM) is present. Indeed, recent photometric modeling studies of SNe, as well as early spectroscopy, suggest that such dense CSM may be present more often than previously expected. If true, this should also affect the features of SBO. We present an exploration of the impact of such CSM interaction on the SBO width and luminosity using both analytic and numerical modeling, where we parameterize the CSM as a steady-state wind. We then compare this modeling to PS1-13arp, an SN that showed an early UV excess that has been argued to be SBO in dense CSM. We find PS1-13arp is well fit with a wind of mass ∼0.08 M_⊙ and radius ∼1900 R_⊙, parameters which are similar to, if not slightly less massive than, what have been inferred for Type II SNe using photometric modeling. This similarity suggests that future SBO observations of SNe II may be easier to obtain than previously appreciated.

In the first paper of this series, we demonstrated that neural networks can robustly and efficiently estimate kinematic parameters for optical emission-line spectra taken by SITELLE at the Canada–France–Hawaii Telescope. This paper expands upon this notion by developing an artificial neural network to estimate the line ratios of strong emission lines present in the SN1, SN2, and SN3 filters of SITELLE. We construct a set of 50,000 synthetic spectra using line ratios taken from the Mexican Million Model database replicating Hii regions. Residual analysis of the network on the test set reveals the network's ability to apply tight constraints to the line ratios. We verified the network's efficacy by constructing an activation map, checking the [Nii] doublet fixed ratio, and applying a standard k-fold cross-correlation. Additionally, we apply the network to SITELLE observations of M33; the residuals between the algorithm's estimates and values calculated using standard fitting methods show general agreement. Moreover, the neural network reduces the computational costs by two orders of magnitude. Although standard fitting routines do consistently well depending on the signal-to-noise ratio of the spectral features, the neural network can also excels at predictions in the low signal-to-noise regime within the controlled environment of the training set as well as on observed data when the source spectral properties are well constrained by models. These results reinforce the power of machine learning in spectral analysis.

Laboratory experiments revealed that CO₂ ice particles stick less efficiently than H₂O ice particles, and there is an order of magnitude difference in the threshold velocity for sticking. However, the surface energies and elastic moduli of CO₂ and H₂O ices are comparable, and the reason why CO₂ ice particles were poorly sticky compared to H₂O ice particles was unclear. Here we investigate the effects of viscoelastic dissipation on the threshold velocity for sticking of ice particles using the viscoelastic contact model derived by Krijt et al. We find that the threshold velocity for the sticking of CO₂ ice particles reported in experimental studies is comparable to that predicted for perfectly elastic spheres. In contrast, the threshold velocity for the sticking of H₂O ice particles is an order of magnitude higher than that predicted for perfectly elastic spheres. Therefore, we conclude that the large difference in stickiness between CO₂ and H₂O ice particles would mainly originate from the difference in the strength of viscoelastic dissipation, which is controlled by the viscoelastic relaxation time.

We use the ∼370 deg² data from the MWISP CO survey to study the vertical distribution of the molecular clouds (MCs) toward the tangent points in the region of l = [+16°, +52°] and ∣b∣ < 51. We find that the molecular disk consists of two components with a layer thickness (FWHM) of ∼85 pc and ∼280 pc, respectively. In the inner Galaxy, the molecular mass in the thin disk is dominant, while the molecular mass traced by the discrete MCs with weak CO emission in the thick disk is probably ≲10% of the whole molecular disk. For the CO gas in the thick disk, we identified 1055 high-z MCs that are ≳100 pc from the Galactic plane. However, only a few samples (i.e., 32 MCs or 3%) are located in the ∣z∣ ≳ 360 pc region. Typically, the discrete MCs of the thick-disk population have a median peak temperature of 2.1 K, a median velocity dispersion of 0.8 km s⁻¹, and a median effective radius of 2.5 pc. Assuming a constant value of X_CO = 2 × 10²⁰ cm⁻²(K km s⁻¹)⁻¹, the median surface density of these MCs is 6.8 M_⊙ pc⁻², indicating very faint CO emission for the high-z gas. The cloud–cloud velocity dispersion is 4.9 ± 1.3 km s⁻¹ and a linear variation with a slope of ∼−0.4 km s⁻¹ kpc⁻¹ is obtained in the region of R_GC = 2.2–6.4 kpc. Assuming that these clouds are supported by their turbulent motions against the gravitational pull of the disk, a model of ρ₀(R) = 1.28 M_⊙ pc⁻³${e}^{-\displaystyle \frac{R}{3.2\mathrm{kpc}}}$ can be used to describe the distribution of the total mass density in the Galactic midplane.

We are undertaking the first systematic infrared (IR) census of R Coronae Borealis (RCB) stars in the Milky Way, beginning with IR light curves from the Palomar Gattini IR (PGIR) survey. The PGIR is a 30 cm J-band telescope with a 25 deg² camera that is surveying 18,000 deg² of the northern sky (δ > −28°) at a cadence of 2 days. We present PGIR light curves for 922 RCB candidates selected from a mid-IR color-based catalog. Of these 922, 149 are promising RCB candidates, as they show pulsations or declines similar to RCB stars. The majority of the candidates that are not RCB stars are either long-period variables (LPVs) or RV Tauri stars. We identify IR color-based criteria to better distinguish between RCB stars and LPVs. As part of a pilot spectroscopic run, we obtain NIR spectra for 26 of the 149 promising candidates and spectroscopically confirm 11 new RCB stars. We detect strong He iλ10830 features in the spectra of all RCB stars, likely originating within high-velocity (200–400 km s⁻¹) winds in their atmospheres. Nine of these RCB stars show ¹²C¹⁶O and ¹²C¹⁸O molecular absorption features, suggesting that they are formed through a white dwarf merger. We detect quasiperiodic pulsations in the light curves of five RCB stars. The periods range between 30 and 125 days and likely originate from the strange-mode instability in these stars. Our pilot run results motivate a dedicated IR spectroscopic campaign to classify all RCB candidates.

As many as 10% of OB-type stars have global magnetic fields, which is surprising given that their internal structure is radiative near the surface. A direct probe of internal structure is pulsations, and some OB-type stars exhibit pressure modes (β Cep pulsators) or gravity modes (slowly pulsating B-type stars; SPBs); a few rare cases of hybrid β Cep/SPBs occupy a narrow instability strip in the H-R diagram. The most precise fundamental properties of stars are obtained from eclipsing binaries (EBs), and those in clusters with known ages and metallicities provide the most stringent constraints on theory. Here we report the discovery that HD 149834 in the ∼5 Myr cluster NGC 6193 is an EB comprising a hybrid β Cep/SPB pulsator and a highly irradiated low-mass companion. We determine the masses, radii, and temperatures of both stars; the ∼9.7 M_⊙ primary resides in the instability strip where hybrid pulsations are theoretically predicted. The presence of both SPB and β Cep pulsations indicates that the system has a near-solar metallicity, and is in the second half of the main-sequence lifetime. The radius of the ∼1.2 M_⊙ companion is consistent with theoretical pre-main-sequence isochrones at 5 Myr, but its temperature is much higher than expected, perhaps due to irradiation by the primary. The radius of the primary is larger than expected, unless its metallicity is super-solar. Finally, the light curve shows residual modulation consistent with the rotation of the primary, and Chandra observations reveal a flare, both of which suggest the presence of starspots and thus magnetism on the primary.

The detection of GeV γ-ray emission from Galactic novae by the Fermi-Large Area Telescope has become routine since 2010, and is generally associated with shocks internal to the nova ejecta. These shocks are also expected to heat plasma to ∼10⁷ K, resulting in detectable X-ray emission. In this paper, we investigate 13 γ-ray emitting novae observed with the Neil Gehrels Swift Observatory, searching for 1–10 keV X-ray emission concurrent with γ-ray detections. We also analyze γ-ray observations of novae V407 Lup (2016) and V357 Mus (2018). We find that most novae do eventually show X-ray evidence of hot shocked plasma, but not until the γ-rays have faded below detectability. We suggest that the delayed rise of the X-ray emission is due to large absorbing columns and/or X-ray suppression by corrugated shock fronts. The only nova in our sample with a concurrent X-ray/γ-ray detection is also the only embedded nova (V407 Cyg). This exception supports a scenario where novae with giant companions produce shocks with external circumbinary material and are characterized by lower density environments, in comparison with novae with dwarf companions where shocks occur internal to the dense ejecta.

We present constraints on the physical properties (including stellar mass, age, and star formation rate) of 207 6 ≲ z ≲ 8 galaxy candidates from the Reionization Lensing Cluster Survey (RELICS) and Spitzer-RELICS surveys. We measure photometry using T-PHOT and perform spectral energy distribution fitting using EAzY and BAGPIPES. Of the 207 candidates for which we could successfully measure (or place limits on) Spitzer fluxes, 23 were demoted to likely z < 4. Among the high-z candidates, we find intrinsic stellar masses between 1 × 10⁶M_⊙ and 4 × 10⁹M_⊙, and rest-frame UV absolute magnitudes between −22.6 and −14.5 mag. While our sample is mostly comprised of ${L}_{m\mathrm{UV}}/{L}_{m\mathrm{UV}}^{* }\lt 1$ galaxies, it extends to ${L}_{m\mathrm{UV}}/{L}_{m\mathrm{UV}}^{* }\sim 2$. Our sample spans ∼4 orders of magnitude in stellar mass and star formation rates, and exhibits ages that range from maximally young to maximally old. We highlight 11 z ≥ 6.5 galaxies with detections in Spitzer/IRAC imaging, several of which show evidence for some combination of evolved stellar populations, large contributions of nebular emission lines, and/or dust. Among these is PLCKG287+32-2013, one of the brightest z ∼ 7 candidates known (AB mag 24.9 at 1.6 μm) with a Spitzer 3.6 μm flux excess suggesting strong [O iii] + H-β emission (∼1000 Å rest-frame equivalent width). We discuss the possible uses and limits of our sample and present a public catalog of Hubble + Spitzer photometry along with physical property estimates for all objects in the sample. Because of their apparent brightnesses, high redshifts, and variety of stellar populations, these objects are excellent targets for follow-up with the James Webb Space Telescope.

We present a new generation of model calculations for cosmogenic production rates in various types of solar system bodies. The model is based on the spectra for primary and secondary particles calculated using the INCL++6 code, which is the most reliable and most sophisticated code available for spallation reactions. Thanks to the recent improvements (extending the code to lower and higher energies and considering light charged particles as ejectiles and projectiles), we can for the first time directly consider primary and secondary Galactic α particles. We calculate production rates for ²²Na, ¹⁰Be, and ²⁶Al in an L-chondrite with a radius of 45 cm and in the Apollo 15 drill core, and we determine the long-term average Galactic cosmic-ray (GCR) spectrum (represented by the solar modulation potential Φ) in the meteoroid orbits at ∼3 au of Φ = 600 MV and at 1 au, i.e., for Earth and Moon of Φ = 660 MV. From this, we calculate a long-term average GCR gradient in the inner solar system of ∼5% au⁻¹. Finally, we discuss the possibility of studying temporal GCR variations and meteoroid orbits using production rate ratios of short- and long-lived radionuclides.

We examine the correlations of star formation rate (SFR) and gas-phase metallicity Z. We first predict how the SFR, cold gas mass, and Z will change with variations in inflow rate or in star formation efficiency (SFE) in a simple gas-regulator framework. The changes ${\rm{\Delta }}\mathrm{log}$ SFR and ${\rm{\Delta }}\mathrm{log}Z$ are found to be negatively (positively) correlated when driving the gas regulator with time-varying inflow rate (SFE). We then study the correlation of ${\rm{\Delta }}\mathrm{log}$ sSFR (specific SFR) and ${\rm{\Delta }}\mathrm{log}$(O/H) from observations, at both ∼100 pc and galactic scales, based on two two-dimensional spectroscopic surveys with different spatial resolutions, MAD and MaNGA. After taking out the overall mass and radial dependences, which may reflect changes in inflow gas metallicity and/or outflow mass loading, we find that ${\rm{\Delta }}\mathrm{log}$ sSFR and ${\rm{\Delta }}\mathrm{log}$(O/H) on galactic scales are found to be negatively correlated, but ${\rm{\Delta }}\mathrm{log}$ sSFR and ${\rm{\Delta }}\mathrm{log}$(O/H) are positively correlated on ∼100 pc scales within galaxies. If we assume that the variations across the population reflect temporal variations in individual objects, we conclude that variations in the SFR are primarily driven by time-varying inflow at galactic scales and driven by time-varying SFE at ∼100 pc scales. We build a theoretical framework to understand the correlation between SFR, gas mass, and metallicity, as well as their variability, which potentially uncovers the relevant physical processes of star formation at different scales.

Galactic black hole candidate GX 339-4 underwent several outbursting phases in the past two and a half decades at irregular intervals of 2–3 years. The nature of these outbursts in terms of the duration, number of peaks, maximum peak intensity, and so on varies. We present a possible physical reason behind the variation of the outbursts. From a physical point of view, if the supply of matter from the companion is roughly constant, the total energy released in an outburst is expected to be proportional to the quiescent period prior to the outburst when the matter is accumulated. We use archival data of RXTE/ASM from 1996 January to 2011 June and of MAXI/GSC from 2009 August to 2020 July. Five initial outbursts of GX 339-4 between 1997 and 2011 were observed by ASM and showed a good linear relation between the accumulation period and the amount of energy released in each outburst, but the outbursts after 2013 behaved quite differently. The 2013, 2017–2018, and 2018–2019 outbursts were of short duration and incomplete or "failed" in nature. We suggest that the matter accumulated during the quiescent periods prior to these outbursts was not cleared through accretion due to a lack of viscosity. The leftover matter was cleared in the very next outbursts. Our study thus sheds light on long-term accretion dynamics in outbursting sources.

Outflows of ionized gas driven by active galactic nuclei (AGN) may significantly impact the evolution of their host galaxies. However, determining the energetics of these outflows is difficult with spatially unresolved observations that are subject to strong global selection effects. We present part of an ongoing study using Hubble Space Telescope and Apache Point Observatory spectroscopy and imaging to derive spatially resolved mass outflow rates and energetics for narrow-line region outflows in nearby AGN that are based on multi-component photoionization models to account for spatial variations in gas ionization, density, abundances, and dust content. This expanded analysis adds Mrk 3, Mrk 78, and NGC 1068, doubling our earlier sample. We find that the outflows contain total ionized gas masses of M ≈ 10^5.5–10^7.5M_⊙ and reach peak velocities of v ≈ 800–2000 km s⁻¹. The outflows reach maximum mass outflow rates of ${\dot{M}}_{\mathrm{out}}\approx 3\mbox{--}12\,{M}_{\odot }$ yr⁻¹ and encompass total kinetic energies of E ≈ 10⁵⁴–10⁵⁶ erg. The outflows extend to radial distances of r ≈ 0.1–3 kpc from the nucleus, with the gas masses, outflow energetics, and radial extents positively correlated with AGN luminosity. The outflow rates are consistent with in situ ionization and acceleration where gas is radiatively driven at multiple radii. These radial variations indicate that spatially resolved observations are essential for localizing AGN feedback and determining the most accurate outflow parameters.

The anomalous diffusion of resonant protons in parallel and perpendicular velocity space by kinetic Alfvén waves is discussed. The velocity diffusion coefficient is calculated by employing an autocorrelation function for proton trajectories. It is found that for protons resonant with the waves, the perpendicular diffusion coefficient decays away for a sufficiently long time, but parallel diffusion monotonically increases in time until it saturates at a certain level. This result indicates that a portion of resonant protons can undergo anomalous diffusion along the background magnetic field even if the intensity of the kinetic Alfvén wave is sufficiently low. The present findings imply that under suitable conditions, astrophysical charged-particle acceleration can take place in the parallel direction.

We have analyzed ALMA Cycle 5 data in Band 4 toward three low-mass young stellar objects, IRAS 03235+3004 (hereafter IRAS 03235), IRAS 03245+3002 (IRAS 03245), and IRAS 03271+3013 (IRAS 03271), in the Perseus region. The HC₃N (J = 16–15; E_up/k = 59.4 K) line has been detected in all of the target sources, while four CH₃OH lines (E_up/k = 15.4–36.3 K) have been detected only in IRAS 03245. Sizes of the HC₃N distributions (∼2930–3230 au) in IRAS 03235 and IRAS 03245 are similar to those of the carbon-chain species in the warm carbon-chain chemistry (WCCC) source L1527. The size of the CH₃OH emission in IRAS 03245 is ∼1760 au, which is slightly smaller than that of HC₃N in this source. We compare the CH₃OH/HC₃N abundance ratios observed in these sources with predictions of chemical models. We confirm that the observed ratio in IRAS 03245 agrees with the modeled values at temperatures around 30–35 K, which supports the HC₃N formation by the WCCC mechanism. In this temperature range, CH₃OH does not thermally desorb from dust grains. Nonthermal desorption mechanisms or gas-phase formation of CH₃OH seem to work efficiently around IRAS 03245. The fact that IRAS 03245 has the highest bolometric luminosity among the target sources seems to support these mechanisms, in particular the nonthermal desorption mechanisms.

The electron-impact excitations from the ground state to the excited levels $1{s}^{2}2{s}^{2}2{p}_{1/2}^{5}3{d}_{3/2}\,J=1$ and $1{s}^{2}2{s}^{2}2{p}_{3/2}^{5}3{d}_{5/2}\,J=1$ as well as the subsequent radiative decays of neonlike Fe¹⁶⁺ ions have been investigated within the framework of the multiconfigurational Dirac–Fock method and the relativistic distorted-wave theory. Special attention has been paid to emission behaviors of the astrophysically relevant resonance 3C and intercombination 3D lines emitted in the radiative decays of Fe¹⁶⁺ ions. To this end, we calculate the angular distribution and linear polarization of both of the lines for a series of impact electron energies. It is found that the angular and polarization behaviors of the resonance 3C line are nearly the same as those of the intercombination 3D line. Nevertheless, the angular and polarization behaviors of both of the lines are found to be very sensitive to the impact electron energy, especially at low impact energies. Based on such a sensitivity, it is expected that high-precision angular and polarization measurements of the 3C and 3D lines could be served as a tool for revealing detailed information such as electron energy of relevant laboratory and astrophysical plasmas.

We present the first observational constraint on the Brackett-γ (Brγ) recombination line emission associated with the supermassive black hole at the center of our Galaxy, known as Sgr A*. By combining 13 yr of data with the adaptive optics fed integral field spectrograph OSIRIS at the W. M. Keck Observatory obtained as part of the Galactic Center Orbits Initiative, we extract the near-infrared spectrum within ∼0.2'' of the black hole and we derive an upper limit on the Brγ flux. The aperture was set to match the size of the disk-like structure that was recently reported based on millimeter-wave Atacama Large Millimeter/submillimeter Array (ALMA) observations of the hydrogen recombination line, H30α. Our stringent upper limit is at least a factor of 80 (and up to a factor of 245) below what would be expected from the ALMA measurements and strongly constrains possible interpretation of emission from this highly underluminous supermassive black hole.

We report on the X-ray properties of the new transient Swift J0840.7−3516, discovered with Swift/BAT in 2020 February, using extensive data from Swift, MAXI, NICER, and NuSTAR. The source flux increased for ∼10³ s after the discovery, decayed rapidly over ∼5 orders of magnitude in five days, and then remained almost constant over nine months. Large-amplitude short-term variations on timescales of 1–10⁴ s were observed throughout the decay. In the initial flux rise, the source showed a hard power-law-shaped spectrum with a photon index of ∼1.0 extending up to ∼30 keV, above which an exponential cutoff was present. The photon index increased in the following rapid decay and became ∼2 at the end of the decay. A spectral absorption feature at 3–4 keV was detected in the decay. It is not straightforward to explain all the observed properties by any known class of X-ray sources. We discuss the possible nature of the source, including a Galactic low-mass X-ray binary with multiple extreme properties and a tidal disruption event by a supermassive black hole or a Galactic neutron star.

The internal composition of neutron stars is currently largely unknown. Due to the possibility of phase transitions in quantum chromodynamics, stars could be hybrid and have quark cores. We investigate some imprints of elastic quark phases (only when perturbed) on the dynamical stability of hybrid stars. We show that they increase the dynamical stability window of hybrid stars in the sense that the onset of instabilities happens at larger central densities than the ones for maximum masses. In particular, when the shear modulus of a crystalline quark phase is taken at face value, the relative radius differences between elastic and perfect-fluid hybrid stars with null radial frequencies (onset of instability) would be up to 1%–2%. Roughly, this would imply a maximum relative radius dispersion (on top of the perfect-fluid predictions) of 2%–4% for stars in a given mass range exclusively due to the elasticity of the quark phase. In the more agnostic approach where the estimates for the quark shear modulus only suggest its possible order of magnitude (due to the many approximations taken in its calculation), the relative radius dispersion uniquely due to a quark phase elasticity might be as large as 5%–10%. Finally, we discuss possible implications of the above dispersion of radii for the constraint of the elasticity of a quark phase with electromagnetic missions such as NICER, eXTP, and ATHENA.

The core mass of galaxy clusters is an important probe of structure formation. Here we evaluate the use of a single-halo model (SHM) as an efficient method to estimate the strong lensing cluster core mass, testing it with ray-traced images from the Outer Rim simulation. Unlike detailed lens models, the SHM represents the cluster mass distribution with a single halo and can be automatically generated from the measured lensing constraints. We find that the projected core mass estimated with this method, M_SHM, has a scatter of 8.52% and a bias of 0.90% compared to the "true" mass within the same aperture. Our analysis shows no systematic correlation between the scatter or bias and the lens-source system properties. The bias and scatter can be reduced to 3.26% and 0.34%, respectively, by excluding models that fail a visual inspection test. We find that the SHM success depends on the lensing geometry, with single giant arc configurations accounting for most of the failed cases due to their limiting constraining power. When excluding such cases, we measure a scatter and bias of 3.88% and 0.84%, respectively. Finally, we find that when the source redshift is unknown, the model-predicted redshifts are overestimated, and the M_SHM is underestimated by a few percent, highlighting the importance of securing spectroscopic redshifts of background sources. Our analysis provides a quantitative characterization of M_SHM, enabling its efficient use as a tool to estimate the strong lensing cluster core masses in the large samples, expected from current and future surveys.

The Canadian Hydrogen Intensity Mapping Experiment (CHIME) has become a leading facility for detecting fast radio bursts (FRBs) through the CHIME/FRB backend. CHIME/FRB searches for fast transients in polarization-summed intensity data streams that have 24 kHz spectral and 1 ms temporal resolution. The intensity beams are pointed to predetermined locations in the sky. A triggered baseband system records the coherent electric field measured by each antenna in the CHIME array at the time of FRB detections. Here we describe the analysis techniques and automated pipeline developed to process these full-array baseband data recordings. Whereas the real-time FRB detection pipeline has a localization limit of several arcminutes, offline analysis of baseband data yields source localizations with subarcminute precision, as characterized by using a sample of pulsars and one repeating FRB with known positions. The baseband pipeline also enables resolving temporal substructure on a microsecond scale and the study of polarization including detections of Faraday rotation.

Using the Atacama Large Millimeter/submillimeter Array (ALMA), we investigated the peculiar millimeter source MMS 3 located in the Orion Molecular Cloud 3 (OMC-3) region in the 1.3 mm continuum, CO (J = 2–1), SiO (J = 5–4), C¹⁸O (J = 2–1), N₂D⁺ (J = 3–2), and DCN (J = 3–2) emissions. With the ALMA high angular resolution (∼02), we detected a very compact and highly centrally condensed continuum emission with a size of 045 × 032 (P.A. = 022). The peak position coincides with the locations of previously reported Spitzer/IRAC and X-ray sources within their positional uncertainties. We also detected an envelope with a diameter of ∼6800 au (P.A. = 75°) in the C¹⁸O (J = 2–1) emission. Moreover, a bipolar outflow was detected in the CO (J = 2–1) emission for the first time. The outflow is elongated roughly perpendicular to the long axis of the envelope detected in the C¹⁸O (J = 2–1) emission. Compact high-velocity CO gas in the (redshifted) velocity range of 22–30 km s⁻¹, presumably tracing a jet, was detected near the 1.3 mm continuum peak. A compact and faint redshifted SiO emission was marginally detected in the CO outflow lobe. The physical quantities of the outflow in MMS 3 are somewhat smaller than those in other sources in the OMC-3 region. The centrally condensed object associated with the near-infrared and X-ray sources, the flattened envelope, and the faint outflow indicate that MMS 3 harbors a low-mass protostar with an age of ∼10³ yr.

The formation mechanism of the W50/SS 433 complex has long been a mystery. We propose a new scenario in which the SS 433 jets themselves form the W50/SS 433 system. We carry out magnetohydrodynamics simulations of the propagation of two side jets using the public code CANS+. As found in previous jet studies, when the propagating jet is lighter than the surrounding medium, the shocked plasma flows back from the jet tip to the core. We find that the morphology of light jets is spheroidal at early times; afterward, the shell and wings are developed by the broadening spherical cocoon. The morphology depends strongly on the density ratio of the injected jet to the surrounding medium. Meanwhile, the ratio of the lengths of the two side jets depends only on the density profile of the surrounding medium. We also find that most of the jet kinetic energy is dissipated at the oblique shock formed by the interaction between the backflow and beam flow, rather than at the jet terminal shock. The position of the oblique shock is spatially consistent with the X-ray and TeV gamma-ray hotspots of W50.

The dark matter halos that surround Milky Way–like galaxies in cosmological simulations are, to first order, triaxial. Nearly 30 yr ago it was predicted that such triaxial dark matter halos should exhibit steady figure rotation or tumbling motions for durations of several gigayears. The angular frequency of figure rotation predicted by cosmological simulations is described by a log-normal distribution of pattern speed Ω_p with a median value 0.15 h km s⁻¹ kpc⁻¹ (∼0.15 h rad Gyr⁻¹ ∼ 9° h Gyr⁻¹) and a width of 0.83h km s⁻¹ kpc⁻¹. These pattern speeds are so small that they have generally been considered both unimportant and undetectable. In this work we show that even extremely slow figure rotation can significantly alter the structure of extended stellar streams produced by the tidal disruption of satellites in the Milky Way halo. We simulate the behavior of a Sagittarius-like polar tidal stream in triaxial dark matter halos with different shapes, when the halos are rotated about the three principal axes. For pattern speeds typical of cosmological halos, we demonstrate, for the first time, that a Sagittarius-like tidal stream would be altered to a degree that is detectable even with current observations. This discovery will potentially allow for a future measurement of figure rotation of the Milky Way's dark matter halo, perhaps enabling the first evidence of this relatively unexplored prediction of cold dark matter.

We report the early discovery and multicolor (BVI) high-cadence light-curve analyses of the rapidly declining sub-Chandrasekhar Type Ia supernova KSP-OT-201509b (= AT 2015cx) from the KMTNet Supernova Program. The Phillips and color stretch parameters of KSP-OT-201509b are ΔM_B,15 ≃ 1.62 mag and s_BV ≃ 0.54, respectively, at an inferred redshift of 0.072. These, together with other measured parameters (such as the strength of the secondary I-band peak, colors, and luminosity), identify the source to be a rapidly declining Type Ia of a transitional nature that is closer to Branch-normal than 91bg-like. Its early light-curve evolution and bolometric luminosity are consistent with those of homologously expanding ejecta powered by radioactive decay and a Type Ia SN explosion with 0.32 ± 0.01 M_⊙ of synthesized ⁵⁶Ni mass, 0.84 ± 0.12 M_⊙ of ejecta mass, and (0.61 ± 0.14) × 10⁵¹ erg of ejecta kinetic energy. While its B − V and V − I colors evolve largely synchronously with the changes in the I-band light curve, as found in other supernovae, we also find the presence of an early redward evolution in V − I prior to −10 days since peak. The bolometric light curve of the source is compatible with a stratified ⁵⁶Ni distribution extended to shallow layers of the exploding progenitor. Comparisons between the observed light curves and those predicted from ejecta–companion interactions clearly disfavor Roche lobe–filling companion stars at large separation distances, thus supporting a double-degenerate scenario for its origin. The lack of any apparent host galaxy in our deep stack images reaching a sensitivity limit of ∼28 mag arcsec⁻² makes KSP-OT-201509b a hostless Type Ia supernova and offers new insights into supernova host galaxy environments.

The second LIGO–Virgo catalog of gravitational-wave (GW) transients has more than quadrupled the observational sample of binary black holes. We analyze this catalog using a suite of five state-of-the-art binary black hole population models covering a range of isolated and dynamical formation channels and infer branching fractions between channels as well as constraints on uncertain physical processes that impact the observational properties of mergers. Given our set of formation models, we find significant differences between the branching fractions of the underlying and detectable populations, and the diversity of detections suggests that multiple formation channels are at play. A mixture of channels is strongly preferred over any single channel dominating the detected population: an individual channel does not contribute to more than ≃70% of the observational sample of binary black holes. We calculate the preference between the natal spin assumptions and common-envelope efficiencies in our models, favoring natal spins of isolated black holes of ≲0.1 and marginally preferring common-envelope efficiencies of ≳2.0 while strongly disfavoring highly inefficient common envelopes. We show that it is essential to consider multiple channels when interpreting GW catalogs, as inference on branching fractions and physical prescriptions becomes biased when contributing formation scenarios are not considered or incorrect physical prescriptions are assumed. Although our quantitative results can be affected by uncertain assumptions in model predictions, our methodology is capable of including models with updated theoretical considerations and additional formation channels.

The snowlines of various volatile species in protoplanetary disks are associated with abrupt changes in gas composition and dust physical properties. Volatiles may affect dust growth, as they cover grains with icy mantles that can change the fragmentation velocity of the grains. In turn, dust coagulation, fragmentation, and drift through the gas disk can contribute to the redistribution of volatiles between the ice and gas phases. Here we present the hydrodynamic model FEOSAD for protoplanetary disks with two dust populations and volatile dynamics. We compute the spatial distributions of major volatile molecules (H₂O, CO₂, CH₄, and CO) in the gas, on small and grown dust, and analyze the composition of icy mantles over the initial 0.5 Myr of disk evolution. We show that most of the ice arrives to the surface of the grown dust through coagulation with small grains. Spiral structures and dust rings forming in the disk, as well as photodissociation in the outer regions, lead to the formation of complex snowline shapes and multiple snowlines for each volatile species. During the considered disk evolution, the snowlines shift closer to the star, with their final position being a factor of 4–5 smaller than that at the disk formation epoch. We demonstrate that volatiles tend to collect in the vicinity of their snowlines, both in the ice and gas phases, leading to the formation of thick icy mantles potentially important for dust dynamics. The dust size is affected by a lower fragmentation velocity of bare grains in the model with a higher turbulent viscosity.

Fast reverse shocks (FRSs) cause the magnetosphere to expand, by contrast to the well-known compressions caused by the impact of fast forward shocks (FFS). Usually, FFSs are more geoeffective than FRSs, and consequently the inner magnetosphere dynamic responses to both shock types can be quite different. In this study, we investigate for the first time the radiation belt response to an FRS impact using multi-satellite observations and numerical simulations. Spacecraft on the dayside observed decreases in magnetic field strength and energetic (∼40–475 keV) particle fluxes. Timing analysis shows that the magnetic field signature propagated from the dayside to the nightside magnetosphere. Particles with different energies vary simultaneously at each spacecraft, implying a non-dispersive particle response to the shock. Spacecraft located at lower L-shells did not record any significant signatures. The observations indicate a local time dependence of the response associated with the shock inclination, with the clearest signatures being observed in the dusk–midnight sector. Simulations underestimate the amplitude of the magnetic field variations observed on the nightside. The observed decreases in the electron intensities result from a combination of radial gradient and adiabatic effects. The radial gradients in the spectral index appear to be the dominant contributor to the observed variations of electrons seen on the dayside (near noon and dusk) and on the nightside (near midnight). This study shows that even an FRS can affect the radiation belts significantly and provides an opportunity to understand their dynamic response to a sudden expansion of the magnetosphere.

We studied the reaction of doubly charged carbon C²⁺ (C iii) with molecular hydrogen, a possible source of the high, unexplained abundances of interstellar CH⁺. The experiment was carried out using the cryogenic linear 22-pole radio frequency ion trap. The measured reaction rate coefficient amounts to (1.5 ± 0.2) × 10⁻¹⁰ cm³ s⁻¹, nearly independently of the covered temperature range from 15 to 300 K. In the product distribution study, the C⁺ ion was identified as the dominant product of the reaction. For the CH⁺ production, we determine an upper limit for the reaction rate coefficient at 2 × 10⁻¹² cm³ s⁻¹.

Normal-mode coupling is a technique applied to probe the solar interior using surface observations of oscillations. The technique, which is straightforward to implement, makes more use of the seismic information in the wave field than other comparable local imaging techniques and therefore has the potential to significantly improve current capabilities. Here, we examine supergranulation power spectra using mode-coupling analyses of intermediate-to-high-degree modes by invoking a Cartesian-geometric description of wave propagation under the assumption that the localized patches are much smaller in size than the solar radius. We extract the supergranular power spectrum and compare the results with prior helioseismic studies. Measurements of the dispersion relation and lifetimes of supergranulation, obtained using near surface modes (f and p₁), are in accord with the literature. We show that the cross-coupling between the p₂ and p₃ acoustic modes, which are capable of probing greater depths, are also sensitive to supergranulation.

The Parker Solar Probe mission (PSP) has completed seven orbits around the Sun. The Wide-field Imager for Solar Probe (WISPR) on PSP consists of two visible light heliospheric imagers, which together image the interplanetary medium between 135 and 108° elongation. The PSP/WISPR nominal science observing window occurs during the solar encounters, which take place when the spacecraft (S/C) is within 0.25 au from the Sun. During Orbit 3, an extended science campaign took place while PSP transited between 0.5 and 0.25 au (during both inbound and outbound orbit segments). PSP mission operations implemented a variety of 180° S/C rolls about the S/C-Sun pointing axis during the extended science window. The vantage of the PSP location, combined with the different S/C roll orientations, allowed us to unveil a circumsolar dust density enhancement associated with Venus's orbit. Specifically, we observed an excess brightness band of about 1% at its center over the brightness of the background zodiacal light in all PSP/WISPR images obtained during the extended campaign. We explain this brightness band as due to an increase in the density of the circumsolar dust orbiting the Sun close to the Venusian orbit. The projected latitudinal extent of the ring is estimated at about 0.043 au ± 0.004 au, exhibiting an average density enhancement of the order of 10%. Here, we report and characterize the first comprehensive, pristine observations of the plane-of-sky projection of the dust ring in almost its full 360° longitudinal extension.

Future space-based direct imaging missions will perform low-resolution (R < 100) optical (0.3–1 μm) spectroscopy of planets, thus enabling reflected spectroscopy of cool giants. Reflected light spectroscopy is encoded with rich information about the scattering and absorbing properties of planet atmospheres. Given the diversity of clouds and hazes expected in exoplanets, it is imperative that we solidify the methodology to accurately and precisely retrieve these scattering and absorbing properties that are agnostic to cloud species. In particular, we focus on determining how different cloud parameterizations affect resultant inferences of both cloud and atmospheric composition. We simulate mock observations of the reflected spectra from three top-priority direct imaging cool giant targets with different effective temperatures, ranging from 135 to 533 K. We perform retrievals of cloud structure and molecular abundances on these three planets using four different parameterizations, each with an increasing level of cloud complexity. We find that the retrieved atmospheric and scattering properties depend strongly on the choice of cloud parameterization. For example, parameterizations that are too simplistic tend to overestimate the abundances. Overall, we are unable to retrieve precise/accurate gravity beyond ±50%. Lastly, we find that even reflected light spectroscopy with a low signal-to-noise ratio of 5 and low R = 40 gives cursory zeroth-order insights into the position of the cloud deck relative to the molecular and Rayleigh optical depth level.

The Galactic H ii region luminosity function (LF) is an important metric for understanding global star formation properties of the Milky Way, but only a few studies have been done, and all use relatively small numbers of H ii regions. We use a sample of 797 first Galactic quadrant H ii regions compiled from the Wide-field Infrared Survey Explorer Catalog of Galactic H ii Regions to examine the form of the LF at multiple infrared and radio wavelengths. Our sample is statistically complete for all regions powered by single stars of type O9.5V and earlier. We fit the LF at each wavelength with single and double power laws. Averaging the results from all wavelengths, the mean of the best-fit single power-law index is 〈α〉 = −1.75 ± 0.01. The mean best-fit double power-law indices are 〈α₁〉 = −1.40 ± 0.03 and 〈α₂〉 = −2.33 ± 0.04. We conclude that neither a single nor a double power law is strongly favored over the other. The LFs show some variation when we separate the H ii region sample into subsets by heliocentric distance, physical size, Galactocentric radius, and location relative to the spiral arms, but blending individual H ii regions into larger complexes does not change the value of the power-law indices of the best-fit LF models. The consistency of the power-law indices across multiple wavelengths suggests that the LF is independent of wavelength. This implies that infrared and radio tracers can be employed in place of Hα.

We performed deep observations to search for radio pulsations in the directions of 375 unassociated Fermi Large Area Telescope γ-ray sources using the Giant Metrewave Radio Telescope (GMRT) at 322 and 607 MHz. In this paper we report the discovery of three millisecond pulsars (MSPs), PSR J0248+4230, PSR J1207–5050, and PSR J1536–4948. We conducted follow-up timing observations for ∼5 yr with the GMRT and derived phase-coherent timing models for these MSPs. PSR J0248+4230 and J1207–5050 are isolated MSPs having periodicities of 2.60 ms and 4.84 ms. PSR J1536–4948 is a 3.07 ms pulsar in a binary system with an orbital period of ∼62 days about a companion of a minimum mass of 0.32 M_⊙. We also present multifrequency pulse profiles of these MSPs from the GMRT observations. PSR J1536–4948 is an MSP with an extremely wide pulse profile having multiple components. Using the radio timing ephemeris we subsequently detected γ-ray pulsations from these three MSPs, confirming them as the sources powering the γ-ray emission. For PSR J1536–4948 we performed combined radio–γ-ray timing using ∼11.6 yr of γ-ray pulse times of arrival (TOAs) along with the radio TOAs. PSR J1536–4948 also shows evidence for pulsed γ-ray emission out to above 25 GeV, confirming earlier associations of this MSP with a ≥10 GeV point source. The multiwavelength pulse profiles of all three MSPs offer challenges to models of radio and γ-ray emission in pulsar magnetospheres.

Based on the theoretical description of position–position–velocity (PPV) statistics in Lazarian & Pogosyan, we introduce a new technique called the velocity decomposition algorithm (VDA) for separating the PPV fluctuations arising from velocity and density fluctuations. Using MHD turbulence simulations, we demonstrate its promise in retrieving the velocity fluctuations from the PPV cube in various physical conditions and its prospects in accurately tracing the magnetic field. We find that for localized clouds, the velocity fluctuations are most prominent in the wing part of the spectral line, and they dominate the density fluctuations. The same velocity dominance applies to extended H i regions undergoing galactic rotation. Our numerical experiment demonstrates that velocity channels arising from the cold phase of atomic hydrogen (H i) are still affected by velocity fluctuations at small scales. We apply the VDA to H i GALFA-DR2 data corresponding to the high-velocity cloud HVC186+19-114 and high-latitude galactic diffuse H i data. Our study confirms the crucial role of velocity fluctuations in explaining why linear structures are observed within PPV cubes. We discuss the implications of VDA for both magnetic field studies and predicting polarized galactic emission that acts as the foreground for cosmic microwave background studies. Additionally, we address the controversy related to the filamentary nature of the H i channel maps and explain the importance of velocity fluctuations in the formation of structures in PPV data cubes. VDA will allow astronomers to obtain velocity fluctuations from almost every piece of spectroscopic PPV data and allow direct investigations of the turbulent velocity field in observations.

Post-starburst galaxies are crucial to disentangling the effect of star formation and quenching on galaxy demographics. They comprise, however, a heterogeneous population of objects, described in numerous ways. To obtain a well-defined and uncontaminated sample, we take advantage of spatially resolved spectroscopy to construct an unambiguous sample of E + A galaxies—post-starburst systems with no observed ongoing star formation. Using data from the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) Survey, in the fourth generation of the Sloan Digital Sky Survey (SDSS-IV), we have identified 30 E + A galaxies that lie within the green valley of color–stellar mass space. We first identified E + A candidates by their central, single-fiber spectra and (u–r) color from SDSS DR15, and then further required each galaxy to exhibit E + A properties throughout the entirety of the system to three effective radii. We describe our selection criteria in detail, note common pitfalls in E + A identification, and introduce the basic characteristics of the sample. We will use this E + A sample, which has been assembled with stringent criteria and thus re-establishes a well-defined subpopulation within the broader category of post-starburst galaxies, to study the evolution of galaxies and their stellar populations in the time just after star formation within them is fully quenched.

We perform a linear analysis of the stability of isothermal, rotating, magnetic, self-gravitating sheets that are weakly ionized. The magnetic field and rotation axis are perpendicular to the sheet. We include a self-consistent treatment of thermal pressure, gravitational, rotational, and magnetic (pressure and tension) forces together with two nonideal magnetohydrodynamic (MHD) effects (ohmic dissipation and ambipolar diffusion) that are treated together for their influence on the properties of gravitational instability for a rotating sheetlike cloud or disk. Our results show that there is always a preferred length scale and associated minimum timescale for gravitational instability. We investigate their dependence on important dimensionless free parameters of the problem: the initial normalized mass-to-flux ratio μ₀, the rotational Toomre parameter Q, the dimensionless ohmic diffusivity ${\tilde{\eta }}_{\mathrm{OD},0}$, and the dimensionless neutral–ion collision time ${\tilde{\tau }}_{\mathrm{ni},0}$, which is a measure of the ambipolar diffusivity. One consequence of ${\tilde{\eta }}_{\mathrm{OD},0}$ is that there is a maximum preferred length scale of instability that occurs in the transcritical (μ₀ ≳ 1) regime, qualitatively similar to the effect of ${\tilde{\tau }}_{\mathrm{ni},0}$, but with quantitative differences. The addition of rotation leads to a generalized Toomre criterion (that includes a magnetic dependence) and modified length scales and timescales for collapse. When nonideal MHD effects are also included, the Toomre criterion reverts back to the hydrodynamic value. We apply our results to protostellar disk properties in the early embedded phase and find that the preferred scale of instability can significantly exceed the thermal (Jeans) scale and the peak preferred fragmentation mass is likely to be ∼10–90 M_Jup.