Sazuna/UAT_keywords huggingface dataset:
Massive White Dwarfs in the 100 pc Sample: Magnetism, Rotation, Pulsations, and the Merger Fraction. We present a detailed model atmosphere analysis of massive white dwarfs with M &gt; 0.9 M ⊙ and T eff ≥ 11,000 K in the Montreal White Dwarf Database 100 pc sample and the Pan-STARRS footprint. We obtained follow-up optical spectroscopy of 109 objects with no previous spectral classification in the literature. Our spectroscopic follow-up is now complete for all 204 objects in the sample. We find 118 normal DA white dwarfs, including 45 massive DAs near the ZZ Ceti instability strip. There are no normal massive DBs: the six DBs in the sample are strongly magnetic and/or rapidly rotating. There are 20 massive DQ white dwarfs in our sample, and all are found in the crystallization sequence. In addition, 66 targets are magnetic (32% of the sample). We use magnetic white dwarf atmosphere models to constrain the field strength and geometry using offset dipole models. We also use magnetism, kinematics, and rotation measurements to constrain the fraction of merger remnant candidates among this population. The merger fraction of this sample increases from 25% for 0.9─1 M ⊙ white dwarfs to 49% for 1.2─1.3 M ⊙. However, this fraction is as high as  78−7+4 % for 1.1─1.2 M ⊙ white dwarfs. Previous works have demonstrated that 5%─9% of high-mass white dwarfs stop cooling for ∼8 Gyr due to the 22Ne distillation process, which leads to an overdensity of Q-branch stars in the solar neighborhood. We demonstrate that the overabundance of the merger remnant candidates in our sample is likely due to the same process.

Keywords: White dwarf stars, Magnetic fields, Stellar evolution
Type Ia Supernovae from First-generation Stars. Type Ia supernovae (SNe Ia) discovered at redshift z ≲ 2.5 are presumed to be produced from Population I/II stars. In this work, we investigate the production of SNe Ia from Population III binaries in the cosmological framework. We derive the SN Ia rate as a function of redshift in a theoretical context for the production of first-generation stars and evaluate the likelihood of their detection by the James Webb Space Telescope (JWST). Assuming the initial stellar mass function (IMF) favors low-mass stars, as from recent numerical simulations, we found that Population III stars may give rise to a considerable number of SNe Ia at high redshift, and Population III stars may even be the dominant SN Ia producer at z ≳ 6. In an optimistic scenario, we expect ∼1(2) SNe Ia from Population III stars at z ≈ 4(5) for a survey of area  300arcmin2  during a 3 yr period with JWST. The same survey may record more than ∼400 SNe Ia at lower redshift (z ≲ 2.5) but with only about one of them from Population III progenitors. There will be ∼six Population III SNe Ia in the same field of view at redshifts of 5–10. Observational constraints on SN Ia rates at the redshift range of 5–10 can place crucial constraints on the IMF of Population III stars.

Keywords: Cosmology, Population III stars, Type Ia supernovae, Binary stars
X-Ray Bright Active Galactic Nuclei in Local Dwarf Galaxies: Insights from eROSITA. Although supermassive black holes (SMBHs) reside in the heart of virtually every massive galaxy, it remains debated whether dwarf galaxies commonly host SMBHs. Because low-mass galaxies may retain memory of the assembly history of their black holes (BHs), probing the BH occupation fraction of local dwarf galaxies might offer insights into the growth and seeding mechanisms of the first BHs. In this work, we exploit the Western half of the eROSITA all-sky survey (covering 20,000 deg2) and compile a catalog of accreting SMBHs in local (D &lt; 200 Mpc) dwarf galaxies. Cleaning our sample from X-ray background sources, X-ray binaries, and ultraluminous X-ray sources, we identify 74 active galactic nucleus (AGN)─dwarf galaxy pairs. Using this large and uniform sample, we derive the luminosity function of the dwarf galaxy AGN, fitting it with a power-law function and obtaining  dN/dLX=(15.9±2.2)×LX−1.63±0.05 . Measuring the offset between the dwarf galaxies' centroids and the X-ray sources, we find that ≍50% of the AGN are likely off-nuclear, in agreement with theoretical predictions. We compare the BH-to-stellar mass relation of our sample with the local and high-redshift relations, finding that our sources better adhere to the former, which suggests that local AGN across different mass scales undergo similar growth histories. Finally, we compare our sources with semianalytical models: while our sample's shallowness prevents distinguishing between different seeding models, we find that the data favor models that keep SMBHs in dwarf galaxies active at a moderate rate, motivating model improvement by comparison to AGN in the dwarf galaxy regime.

Keywords: Accretion, Supermassive black holes, Dwarf galaxies, X-ray active galactic nuclei
The Reliability of Type Ia Supernovae Delay-time Distributions Recovered from Galaxy Star Formation Histories. We present a numerical analysis investigating the reliability of Type Ia supernova (SN Ia) delay-time distributions recovered from individual host galaxy star formation histories. We utilize star formation histories of mock samples of galaxies generated from the IllustrisTNG simulation at two redshifts to recover delay-time distributions. The delay-time distributions are constructed through piecewise constants as opposed to typically employed parametric forms such as power laws or Gaussian or skew/lognormal functions. The SN Ia delay-time distributions are recovered through a Markov Chain Monte Carlo exploration of the likelihood space by comparing the expected SN Ia rate within each mock galaxy to the observed rate. We show that a reduced representative sample of nonhost galaxies is sufficient to reliably recover delay-time distributions while simultaneously reducing the computational load. We also highlight a potential systematic between recovered delay-time distributions and the mass-weighted ages of the underlying host galaxy stellar population.

Keywords: Computational astronomy, Type Ia supernovae, Galaxies
The Black Hole Mass and Photometric Components of NGC 4826. We present infrared photometry and Hubble Space Telescope imaging and spectroscopy of the Sab galaxy NGC 4826. Schwarzschild dynamical modeling is used to measure its central black hole mass M. Photometric decomposition is used to enable a comparison of M to published scaling relations between black hole masses and properties of host bulges. This decomposition implies that NGC 4826 contains classical and pseudobulges of approximately equal mass. The classical bulge has best-fit Sérsic index n = 3.27. The pseudobulge is made up of three parts, an inner lens (n = 0.18 at r ≲ 4″), an outer lens (n = 0.17 at r ≲ 45″), and a n = 0.58 Sérsic component required to match the surface brightness between the lens components. The total V-band luminosity of the galaxy is M  VT  = ‑21.07, the ratio of classical bulge to total light is B/T ≃ 0.12, and the ratio of pseudobulge to total light is PB/T ≃ 0.13. The outer disk is exponential (n = 1.07) and makes up D/T = 0.75 of the light of the galaxy. Our best-fit Schwarzschild model has a black hole mass with 1σ uncertainties of  M=8.4‑0.6+1.7×106M⊙  and a stellar population with a K-band mass-to-light ratio of  ϒK=0.46±0.03M⊙L⊙‑1  at the assumed distance of 7.27 Mpc. Our modeling is marginally consistent with M = 0 at the 3σ limit. These best-fit parameters were calculated assuming the black hole is located where the velocity dispersion is largest; this is offset from the maximum surface brightness, probably because of dust absorption. The black hole mass—one of the smallest measured by modeling stellar dynamics—satisfies the well known correlations of M with the K-band luminosity, stellar mass, and velocity dispersion of the classical bulge only. In contrast, the black hole is undermassive with respect to the correlation of M with total (classical plus pseudo) bulge luminosity. Thus the composite (classical bulge plus pseudobulge) galaxy NGC 4826 is consistent with previous results on black hole scaling relations and helps to strengthen these results at low black hole masses.

Keywords: Galaxy structure, Galaxy bulges, Black holes, Scaling relations
Cosmic-Ray Feedback on Bistable Interstellar Medium Turbulence. While cosmic rays (E ≳ 1 GeV) are well coupled to a galaxy's interstellar medium (ISM) at scales of L &gt; 100 pc, adjusting stratification and driving outflows, their impact on small scales is less clear. Based on calculations of the cosmic-ray diffusion coefficient from observations of the grammage in the Milky Way, cosmic rays have little time to dynamically impact the ISM on those small scales. Using numerical simulations, we explore how more complex cosmic-ray transport could allow cosmic rays to couple to the ISM on small scales. We create a two-zone model of cosmic-ray transport, with the cosmic-ray diffusion coefficient set at the estimated Milky Way value in cold gas but smaller in warm gas. We compare this model to simulations with a constant diffusion coefficient. Quicker diffusion through cold gas allows more cold gas to form compared to a simulation with a constant, small diffusion coefficient. However, slower diffusion in warm gas allows cosmic rays to take energy from the turbulent cascade anisotropically. This cosmic-ray energization comes at the expense of turbulent energy which would otherwise be lost during radiative cooling. Finally, we show our two-zone model is capable of matching observational estimates of the grammage for some transport paths through the simulation.

Keywords: Magnetohydrodynamical simulations, Interstellar filaments, Cosmic rays
The Peculiar Radio Evolution of the Tidal Disruption Event ASASSN-19bt. We present detailed radio observations of the tidal disruption event (TDE) ASASSN-19bt/AT 2019ahk, obtained with the Australia Telescope Compact Array, the Atacama Large Millimeter/submillimeter Array, and the MeerKAT radio telescopes, spanning 40─1464 days after the onset of the optical flare. We find that ASASSN-19bt displays unusual radio evolution compared to other TDEs, as the peak brightness of its radio emission increases rapidly until 457 days post-optical discovery and then plateaus. Using a generalized approach to standard equipartition techniques, we estimate the energy and corresponding physical parameters for two possible emission geometries: a nonrelativistic spherical outflow and a relativistic outflow observed from a range of viewing angles. We find that the nonrelativistic solution implies a continuous energy rise in the outflow from E ∼ 1046 to E ∼ 1049 erg with outflow speed β ≍ 0.05, while the off-axis relativistic jet solution instead suggests E ≍ 1052 erg with Lorentz factor Γ ∼ 10 at late times in the maximally off-axis case. We find that neither model provides a holistic explanation for the origin and evolution of the radio emission, emphasizing the need for more complex models. ASASSN-19bt joins the population of TDEs that display unusual radio emission at late times. Conducting long-term radio observations of these TDEs, especially during the later phases, will be crucial for understanding how these types of radio emission in TDEs are produced.

Keywords: Accretion, Black hole physics, Jets, Tidal disruption, Radio transient sources
Properties of Solar Wind Current Sheets in the Martian Space Environment. Transient current sheets (CSs) are common magnetic structures in the solar wind that can significantly disturb the planetary space environment and cause space weather phenomena. This study focuses on their properties in the Martian space environment and investigates their transformations caused by the Martian bow shock. Based on 14 months of data from the Mars Atmosphere and Volatile Evolution mission during similar solar activity, 786 CSs with directional changes greater than 90° and magnetic field depression were automatically identified, including 256 events in the upstream solar wind and 530 events in the Martian magnetosheath. After crossing the bow shock, the duration and thickness of the CSs decrease, while their current density and occurrence rate significantly increase. In the Martian magnetosheath, CSs located on the dayside exhibit stronger current density, a relatively lower occurrence rate, and a smaller  Bx/BT  than CSs located on the nightside. From the dayside to the nightside, the predominant magnetic field component of CSs changes to  Bx  due to the draping process. Moreover, a clear dawn–dusk asymmetry in CS properties emerges from the foreshock to the downstream region of the Martian bow shock. Our results reveal the properties and evolution of solar wind CSs in the Martian space environment.

Keywords: Interplanetary discontinuities, Mars, Solar wind
The Metallicity Dependence of PAH Emission in Galaxies. I. Insights from Deep Radial Spitzer Spectroscopy. We use deep Spitzer mid-infrared spectroscopic maps of radial strips across three nearby galaxies with well-studied metallicity gradients (M101, NGC 628, and NGC 2403) to explore the physical origins of the observed deficit of polycyclic aromatic hydrocarbons (PAHs) at subsolar metallicity (i.e., the PAH–metallicity relation or PZR). These maps allow us to trace the evolution of all PAH features from 5–18 μm as metallicity decreases continuously from solar (Z ⊙) to 0.2 Z ⊙. The total PAH-to-dust luminosity ratio remains relatively constant until reaching a threshold of ∼ 2/3 Z ⊙, below which it declines smoothly but rapidly. The PZR has been attributed to preferential destruction of the smallest grains in the hard radiation environments found at low metallicity. In this scenario, a decrease in emission from the shortest-wavelength PAH features is expected. In contrast, we find a steep decline in long-wavelength power below Z ⊙, especially in the 17 μm feature, with the shorter-wavelength PAH bands carrying an increasingly large fraction of power at low metallicity. We use newly developed grain models to reproduce the observed PZR trends, including these variations in fractional PAH feature strengths. The model that best reproduces the data employs an evolving grain size distribution that shifts to smaller sizes as metallicity declines. We interpret this as a result of inhibited grain growth at low metallicity, suggesting continuous replenishment in the interstellar medium is the dominant process shaping the PAH grain population in galaxies.

Keywords: Metallicity, Polycyclic aromatic hydrocarbons, Spiral galaxies
Early Planet Formation in Embedded Disks. XI. A High-resolution View Toward the BHR 71 Class 0 Protostellar Wide Binary. We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of the binary Class 0 protostellar system BHR 71 IRS1 and IRS2 as part of the Early Planet Formation in Embedded Disks (eDisk) ALMA Large Program. We describe the 12CO (J = 2–1), 13CO (J = 2–1), C18O (J = 2–1), H2CO (J = 32,1–22,0), and SiO (J = 5–4) molecular lines along with the 1.3 mm continuum at high spatial resolution (∼0.″08 or ∼5 au). Dust continuum emission is detected toward BHR 71 IRS1 and IRS2, with a central compact component and extended continuum emission. The compact components are smooth and show no sign of substructures such as spirals, rings, or gaps. However, there is a brightness asymmetry along the minor axis of the presumed disk in IRS1, possibly indicative of an inclined geometrically and optically thick disk-like component. Using a position–velocity diagram analysis of the C18O line, clear Keplerian motions were not detected toward either source. If Keplerian rotationally supported disks are present, they are likely deeply embedded in their envelope. However, we can set upper limits of the central protostellar mass of 0.46 M ⊙ and 0.26 M ⊙ for BHR 71 IRS1 and BHR 71 IRS2, respectively. Outflows traced by 12CO and SiO are detected in both sources. The outflows can be divided into two components, a wide-angle outflow and a jet. In IRS1, the jet exhibits a double helical structure, reflecting the removal of angular momentum from the system. In IRS2, the jet is very collimated and shows a chain of knots, suggesting episodic accretion events.

Keywords: Stellar jets, Star formation, Circumstellar disks
Braving the Storm: Quantifying Disk-wide Ionized Outflows in the Large Magellanic Cloud with ULLYSES. The Large Magellanic Cloud (LMC) is home to many H II regions, which may lead to significant outflows. We examine the LMC's multiphase gas (T∼104-5 K) in H I, S II, Si IV, and C IV using 110 stellar sight lines from the Hubble Space Telescope's Ultraviolet Legacy Library of Young Stars as Essential Standards program. We develop a continuum fitting algorithm based on the concept of Gaussian process regression and identify reliable LMC interstellar absorption over v helio = 175–375 km s‑1. Our analyses show disk-wide ionized outflows in Si IV and C IV across the LMC with bulk velocities of ∣v out, bulk∣ ∼ 20–60 km s‑1, which indicates that most of the outflowing mass is gravitationally bound. The outflows' column densities correlate with the LMC's star formation rate surface densities (ΣSFR), and the outflows with higher ΣSFR tend to be more ionized. Considering outflows from both sides of the LMC as traced by C IV, we conservatively estimate a total outflow rate of  Ṁout≳0.03M⊙ yr‑1  and a mass-loading factor of η ≳ 0.15. We compare the LMC's outflows with those detected in starburst galaxies and simulation predictions, and find a universal scaling relation of  ∣vout,bulk∣∝ΣSFR0.23  over a wide range of star-forming conditions (ΣSFR ∼ 10‑4.5–102 M ⊙ yr‑1 kpc‑2). Lastly, we find that the outflows are corotating with the LMC's young stellar disk and the velocity field does not seem to be significantly impacted by external forces; we thus speculate on the existence of a bow shock leading the LMC, which may have shielded the outflows from ram pressure as the LMC orbits the Milky Way.

Keywords: Stellar feedback, Metal line absorbers, Large Magellanic Cloud, Galaxy evolution, Interstellar medium
Efficient Survey Design for Finding High-redshift Galaxies with JWST. Several large JWST blank field observing programs have not yet discovered the first galaxies expected to form at 15 ≤ z ≤ 20. This has motivated the search for more effective survey strategies that will be able to effectively probe this redshift range. Here, we explore the use of gravitationally lensed cluster fields, which have historically been the most effective discovery tool with the Hubble Space Telescope. In this paper, we analyze the effectiveness of the most massive galaxy clusters that provide the highest median magnification factor within a single JWST NIRCam module in uncovering this population. The results of exploiting these lensing clusters to break the z &gt; 15 barrier are compared against the results from large-area, blank-field surveys such as JADES and CEERS in order to determine the most effective survey strategy for JWST. We report that the fields containing massive foreground galaxy clusters specifically chosen to occupy the largest fraction of a single NIRCam module with high magnification factors in the source plane while containing all multiple images in the image plane within a single module provide the highest probability of both probing the 15 ≤ z ≤ 20 regime as well as discovering the highest-redshift galaxy possible with JWST. We also find that using multiple massive clusters in exchange for shallower survey depths is a more time-efficient method of probing the z &gt; 15 regime.

Keywords: Galaxy clusters, Cosmology, Large-scale structure of the universe, Rich galaxy clusters, Abell clusters, High-redshift galaxies, Galaxies
Characterization of the Western Pictor A Hotspot in Hard X-Rays with NuSTAR. The origin of X-ray emission from the resolved kiloparsec-scale jets and hotspots of many active galactic nuclei remains uncertain, particularly where the X-ray emission is separate from the radio-optical synchrotron component. Possible explanations include synchrotron emission from a second electron population and external Compton or synchrotron self-Compton processes—alternatives which imply very different physical conditions within the jet. Until recently, X-ray studies of resolved jets and hotspots have been restricted to below ∼10 keV, often showing a hard spectral index indicating a spectral peak beyond this energy range. Here we present NuSTAR observations of the nearby powerful radio galaxy Pictor A, in which we clearly detect the western hotspot at approximately 4' from the host galaxy, the most significant detection of hotspot emission above 10 keV to date. The NuSTAR spectrum is best fit by a single power law of index Γ = 2.03 ± 0.04; an exponential cutoff gives a 1σ lower limit on the cutoff energy of 40.7 keV. We confirm previous findings of variations in the soft X-ray flux detected by Chandra over the 2000 to 2015 period, at a significance of 6.5σ. This rises to &gt;8σ in the common 3–8 keV band using the combined 22 yr span of Chandra and NuSTAR observations. The variability of the western Pictor A hotspot strongly confirms the previously argued synchrotron nature of the X-ray emission for the hotspot, while the lower bound to the spectral cutoff energy implies electron energies in the hotspot reach up to at least a few TeV.

Keywords: Relativistic jets
TIC 290061484: A Triply Eclipsing Triple System with the Shortest Known Outer Period of 24.5 Days. We have discovered a triply eclipsing triple-star system, TIC 290061484, with the shortest known outer period, P out, of only 24.5 days. This "eclipses" the previous record set by λ Tauri at 33.02 days, which held for 68 yr. The inner binary, with an orbital period of P in = 1.8 days, produces primary and secondary eclipses and exhibits prominent eclipse timing variations with the same periodicity as the outer orbit. The tertiary star eclipses, and is eclipsed by, the inner binary with pronounced asymmetric profiles. The inclinations of both orbits evolve on observable timescales such that the third-body eclipses exhibit dramatic depth variations in TESS data. A photodynamical model provides a complete solution for all orbital and physical parameters of the triple system, showing that the three stars have masses of 6.85, 6.11, and 7.90 M ⊙, radii near those corresponding to the main sequence, and T eff in the range of 21,000─23,700 K. Remarkably, the model shows that the triple is in fact a subsystem of a hierarchical 2+1+1 quadruple with a distant fourth star. The outermost star has a period of ∼3200 days and a mass comparable to the stars in the inner triple. In ∼20 Myr, all three components of the triple subsystem will merge, undergo a Type II supernova explosion, and leave a single remnant neutron star. At the time of writing, TIC 290061484 is the most compact triple system and one of the tighter known compact triples (i.e., P out/P in = 13.7).

Keywords: Eclipsing binary stars, Multiple stars, Binary stars, Close binary stars