adsabs/SciX_UAT_keywords huggingface dataset:
The Formation History of Subhalos and the Evolution of Satellite Galaxies

Satellites constitute an important fraction of the overall galaxy population and are believed to form in dark matter subhalos. Here we use the cosmological hydrodynamic simulation TNG100 to investigate how the formation histories of subhalos affect the properties and evolution of their host galaxies. We use a scaled formation time ( ${a}_{\mathrm{nf}}$ ) to characterize the mass assembly histories of the subhalos before they are accreted by massive host halos. We find that satellite galaxies in young subhalos (low ${a}_{\mathrm{nf}}$ ) are less massive and more gas-rich and have stronger star formation and a higher fraction of ex situ stellar mass than satellites in old subhalos (high ${a}_{\mathrm{nf}}$ ). Furthermore, these low- ${a}_{\mathrm{nf}}$ satellites require longer timescales to be quenched as a population than the high- ${a}_{\mathrm{nf}}$ counterparts. We find very different merger histories between satellites in fast-accretion (FA, ${a}_{\mathrm{nf}}\lt 1.3$ ) and slow-accretion (SA, ${a}_{\mathrm{nf}}\gt 1.3$ ) subhalos. For FA satellites the galaxy merger frequency dramatically increases just after accretion, which enhances the star formation at accretion, whereas for SA satellites the mergers occur smoothly and continuously across the accretion time. Moreover, mergers with FA satellites happen mainly after accretion, while a contrary trend is found for SA satellites. Our results provide insight into the evolution and star formation quenching of the satellite population.

Keywords: galaxy evolution; cosmology; hydrodynamical simulations
Slowdown and Heating of Interstellar Neutral Helium by Elastic Collisions beyond the Heliopause

Direct sampling of interstellar neutral (ISN) atoms close to the Sun enables studies of the very local interstellar medium (VLISM) around the heliosphere. The primary population of ISN helium atoms has, until now, been assumed to reflect the pristine VLISM conditions at the heliopause. Consequently, the atoms observed at 1 au by the Interstellar Boundary Explorer (IBEX) were used to determine the VLISM temperature and velocity relative to the Sun, without accounting for elastic collisions with other species outside the heliopause. Here, we evaluate the effect of these collisions on the primary ISN helium population. We follow trajectories of helium atoms and track their collisions with slowed plasma and interstellar hydrogen atoms ahead of the heliopause. Atoms typically collide a few times in the outer heliosheath, and only ∼1.5% of the atoms are not scattered at all. We use calculated differential cross sections to randomly choose scattering angles in these collisions. We estimate that the resulting primary ISN helium atoms at the heliopause are slowed down by ∼0.45 km s-1 and heated by ∼1100 K compared to the pristine VLISM. The resulting velocity distribution is asymmetric and shows an extended tail in the antisunward direction. Accounting for this change in the parameters derived from IBEX observations gives the Sun's relative speed of 25.85 km s-1 and temperature of 6400 K in the pristine VLISM. Finally, this Letter serves as a source of the differential cross sections for elastic collisions with helium atoms.

Keywords: heliosphere; interstellar atomic gas; interstellar medium; heliopause; heliosheath; interstellar plasma; interstellar abundances
Photon Ring Symmetries in Simulated Linear Polarization Images of Messier 87*

The Event Horizon Telescope (EHT) recently released the first linearly polarized images of the accretion flow around the supermassive black hole Messier 87*, hereafter M87*. The spiraling polarization pattern found in the EHT images favored magnetically arrested disks as the explanation for the EHT image. With next-generation improvements to very long baseline interferometry on the horizon, understanding similar polarized features in the highly lensed structure known as the "photon ring," where photons make multiple half orbits about the black hole before reaching the observer, will be critical to the analysis of future images. Recent work has indicated that this image region may be depolarized relative to more direct emission. We expand this observation by decomposing photon half orbits in the EHT library of simulated images of the M 87* accretion system and find that images of magnetically arrested disk simulations show a relative depolarization of the photon ring attributable to destructive interference of oppositely spiraling electric field vectors; this antisymmetry, which arises purely from strong gravitational lensing, can produce up to ~50% depolarization in the photon ring region with respect to the direct image. In systems that are not magnetically arrested and with the exception of systems with high spin and ions and electrons of equal temperature, we find that highly lensed indirect subimages are almost completely depolarized, causing a modest depolarization of the photon ring region in the complete image. We predict that next-generation EHT observations of M 87* polarization should jointly constrain the black hole spin and the underlying emission and magnetic field geometry.

Keywords: accretion; astrophysical black holes; gravitational lensing; polarimetry; magnetic fields
Generation of High-resolution Solar Pseudo-magnetograms from Ca II K Images by Deep Learning

In this Letter, we generate realistic high-resolution (1024 × 1024 pixels) pseudo-magnetograms from Ca II K images using a deep learning model based on conditional generative adversarial networks. For this, we consider a model "pix2pixHD" that is specifically devised for high-resolution image translation tasks. We use Ca II K 393.3 nm images from the Precision Solar Photometric Telescope at the Rome Observatory and line-of-sight magnetograms from the Helioseismic and Magnetic Imager (HMI) at the Solar Dynamics Observatory from 2011 January to 2015 June. 2465 pairs of Ca II K and HMI are used for training except for January and July data. The remaining 436 pairs are used for an evaluation of the model. Our model shows that the mean correlation coefficient (CC) of total unsigned magnetic flux between AI-generated and real ones is 0.99 and the mean pixel-to-pixel CC after 8 × 8 binning over the full disk is 0.74. We find that the AI-generated absolute magnetic flux densities are highly consistent with real ones, even to the fine scale structures of quiet regions. On the other hand, the mean pixel-to-pixel correlations of magnetic flux densities strongly depend on a region of interest: 0.81 for active regions and 0.24 for quiet regions. Our results suggest a sufficient possibility that we can produce high-resolution solar magnetograms from historical Ca II data.

Keywords: solar physics; the sun; solar atmosphere; solar magnetic fields; astronomy data analysis
Exploring the Magnetic Field Geometry in NGC 891 with SOFIA/HAWC+

Stratospheric Observatory For Infrared Astronomy/High-resolution Airborne Wideband Camera-plus 154 μm Far-Infrared polarimetry observations of the well-studied edge-on galaxy NGC 891 are analyzed and compared to simple disk models with ordered (planar) and turbulent magnetic fields. The overall low magnitude and the narrow dispersion of fractional polarization observed in the disk require significant turbulence and a large number of turbulent decorrelation cells along the line of sight through the plane. Higher surface brightness regions along the major axis to either side of the nucleus show a further reduction in polarization and are consistent with a view tangent to a spiral feature in our disk models. The nucleus also has a similar low polarization, and this is inconsistent with our model spiral galaxy where the ordered magnetic field component would be nearly perpendicular to the line of sight through the nucleus on an edge-on view. A model with a barred spiral morphology with a magnetic field geometry derived from radio synchrotron observations of face-on barred spirals fits the data much better. There is clear evidence for a vertical field extending into the halo from one location in the disk coincident with a polarization null point seen in near-infrared polarimetry, probably due to a blowout caused by star formation. Although our observations were capable of detecting a vertical magnetic field geometry elsewhere in the halo, no clear signature was found. A reduced polarization due to a mix of planar and vertical fields in the dusty regions of the halo best explains our observations, but unusually significant turbulence cannot be ruled out.

Keywords: extragalactic magnetic fields; far infrared astronomy; interstellar medium; spiral galaxies; polarimetry
Discovery of NES, an Extended Tidal Structure in the Northeast of the Large Magellanic Cloud

We report on the discovery of a new diffuse stellar substructure protruding for >5° from the northeastern rim of the LMC disk. The structure, which we dub the northeast structure (NES), was identified by applying a Gaussian mixture model to a sample of strictly selected candidate members of the Magellanic System, extracted from the Gaia EDR3 catalog. The NES fills the gap between the outer LMC disk and other known structures in the same region of the LMC, namely the northern tidal arm and the eastern substructures. Particularly noteworthy is that the NES is placed in a region where N-body simulations foresee a bending of the LMC disk due to tidal stresses induced by the MW. The velocity field in the plane of the sky indicates that the complex of tidal structures in the northeastern part of the LMC, including NES, shows a complex pattern. Additional data, as well as extensive dynamical modeling, is required to shed light onto the origin of NES as well as on the relationships with the surrounding substructures.

Keywords: large magellanic cloud; broad band photometry; proper motions; stellar kinematics; hertzsprung russell diagram; parallax; gaussian mixture model; galaxy interactions
The Oxygen Isotopic Composition of Samples Returned from Asteroid Ryugu with Implications for the Nature of the Parent Planetesimal

We present oxygen isotopic analyses of fragments of the near-Earth Cb-type asteroid Ryugu returned by the Hayabusa2 spacecraft that reinforce the close correspondence between Ryugu and CI chondrites. Small differences between Ryugu samples and CI chondrites in ${{\rm{\Delta }}}^{{\prime} 17}{\rm{O}}$ can be explained at least in part by contamination of the latter by terrestrial water. The discovery that a randomly sampled C-complex asteroid is composed of CI-chondrite-like rock, combined with thermal models for formation prior to significant decay of the short-lived radioisotope 26Al, suggests that if lithified at the time of alteration, the parent body was small (≪50 km radius). If the parent planetesimal was large (>50 km in radius), it was likely composed of high-permeability, poorly lithified sediment rather than consolidated rock.

Keywords: asteroids; planetary thermal histories; carbonaceous chondrites
The Stochastic X-Ray Variability of the Accreting Millisecond Pulsar IGR J17062-6143

This work presents an investigation of the stochastic X-ray variability from the 164 Hz accreting millisecond pulsar IGR J17062-6143, based on regular observations collected with the Neutron Star Interior Composition Explorer between 2017 July and 2020 August. Over this period, the power-density spectrum showed a stable morphology, with broad ~25% rms band-limited noise below 16 Hz. Quasi-periodic oscillations (QPOs) were occasionally observed, with the most notable detections including a low-frequency QPO centered at 2.7 Hz and a sharp QPO centered at 115 Hz that may be a 2:3 resonance with the spin frequency. Further, the energy dependence of the band-limited noise is studied through a spectroscopic analysis of the complex covariance in two frequency intervals. It is found that the power-law continuum is the primary driver for the observed variability, although the thermal (blackbody) emission also appears to be intrinsically variable in area (5% rms) and temperature (1% rms). Notably, the 1 keV emission feature seen in all X-ray spectra of IGR J17062-6143 varies with the same amplitude as the power-law emission, but systematically lags behind that continuum emission. These results appear consistent with a scenario in which a time-variable Compton scattering corona is the primary source for the observed stochastic variability, with the variability observed in the emission feature and at the lowest photon energies being due to the disk reflection of the power-law continuum.

Keywords: low-mass x-ray binary stars; millisecond pulsars
A Geometric Model to Interpret the γ-Ray Quasiperiodic Oscillation of PG 1553+113

We propose a jet helical motion model to explain the γ-ray quasiperiodic oscillation of PG 1553+113. In this model, we hypothesize that a relativistic jet with constant angular velocity rotates around the axis, causing the Doppler factor of the jet to vary over time, leading to periodic changes in flux. In addition, we consider that the parameters of the emission field vary slightly during the observation period and can be obtained by directly fitting their multiwavelength spectra. Then, we use the resulting emission field information and the model to reproduce the light curve. Our model successfully explains the 2.18 ± 0.08 yr γ quasiperiodic oscillation of PG 1553+113, which is consistent with previous studies. Most importantly, we notice an upward trend in the light curve, and we suggest that this upward trend is due to long-term variability with a timescale of ~42 yr.

Keywords: active galaxies; bl lacertae objects; non-thermal radiation sources
Clustered Formation of Massive Stars within an Ionized Rotating Disk

We present Atacama Large Millimeter/submillimeter Array observations with a 800 au resolution and radiative-transfer modeling of the inner part (r ≈ 6000 au) of the ionized accretion flow around a compact star cluster in formation at the center of the luminous ultracompact H II region G10.6-0.4. We modeled the flow with an ionized Keplerian disk with and without radial motions in its outer part, or with an external Ulrich envelope. The Markov Chain Monte Carlo fits to the data give total stellar masses M ⋆ from 120 to 200 M ⊙, with much smaller ionized-gas masses M ion-gas = 0.2-0.25 M ⊙. The stellar mass is distributed within the gravitational radius R g ≈ 1000 to 1500 au, where the ionized gas is bound. The viewing inclination angle from the face-on orientation is i = 49°-56°. Radial motions at radii r > R g converge to v r,0 ≈ 8.7 km s-1, or about the speed of sound of ionized gas, indicating that this gas is marginally unbound at most. From additional constraints on the ionizing-photon rate and far-IR luminosity of the region, we conclude that the stellar cluster consists of a few massive stars with M star = 32-60 M ⊙, or one star in this range of masses accompanied by a population of lower-mass stars. Any active accretion of ionized gas onto the massive (proto)stars is residual. The inferred cluster density is very large, comparable to that reported at similar scales in the Galactic center. Stellar interactions are likely to occur within the next million years.

Keywords: h ii regions
Gaia DR3 Data of Very Young Open Cluster NGC 6530: Distance and Evolutionary Stage of Selected Stars

Gaia EDR3 and Gaia DR3 data of selected stars in the very young (1.5 million years old) open cluster NGC 6530 are presented. All the selected stars have very accurate Gaia DR3 distances. Most of the selected stars are very young B stars and several of them are young stellar objects. From the analysis of selected stars, the distance to NGC 6530 is found to be 1318 pc. The two very red stars VAJ 304 and 338 have little bit less proper motion than other members of the NGC 6530 and their Mv values are found to be ‑3.57 and ‑3.68 respectively. They are much brighter than K5 III RGB stars and less luminous than massive K5 red supergiants. It is likely VAJ 304 and VAJ 338 are not members of NGC 6530 they may be field K5 type AGB or post-AGB stars. Further study of these two stars is needed.

Keywords: open star clusters
Survival Times of Supramassive Neutron Stars Resulting from Binary Neutron Star Mergers

A binary neutron star (BNS) merger can lead to various outcomes, from indefinitely stable neutron stars, through supramassive neutron stars (SMNSs) or hypermassive neutron stars supported only temporarily against gravity, to black holes formed promptly after the merger. Up-to-date constraints on the BNS total mass and the neutron star equation of state suggest that a long-lived SMNS may form in ~0.45-0.9 of BNS mergers. A maximally rotating SMNS needs to lose ~(3-6) × 1052 erg of its rotational energy before it collapses, on a fraction of the spin-down timescale. An SMNS formation imprints on the electromagnetic counterparts to the BNS merger. However, a comparison with observations reveals tensions. First, the distribution of collapse times is too wide and that of released energies too narrow (and the energy itself too large) to explain the observed distributions of internal X-ray plateaus, invoked as evidence for SMNS-powered energy injection. Second, the immense energy injection into the blast wave should lead to extremely bright radio transients, which previous studies found to be inconsistent with deep radio observations of short gamma-ray bursts (GRBs). Furthermore, we show that upcoming all-sky radio surveys will constrain the extracted energy distribution, independently of a GRB jet formation. Our results can be self-consistently understood, provided that most BNS merger remnants collapse shortly after formation (even if their masses are low enough to allow for SMNS formation). This naturally occurs if the remnant retains half or less of its initial energy by the time it enters solid-body rotation.

Keywords: gamma-ray bursts; neutron stars; gravitational waves
Spatially Resolved UV Diagnostics of AGN Feedback: Radiation Pressure Dominates in a Prototypical Quasar-driven Superwind

Galactic-scale winds driven by active galactic nuclei (AGN) are often invoked to suppress star formation in galaxy evolution models, but the mechanisms driving these outflows are hotly debated. Two key AGN feedback models are (1) radiation pressure accelerating cool gas and (2) a hot outflowing wind entraining the interstellar medium (ISM). Highly ionized emission-line diagnostics represent a powerful means of differentiating these scenarios because of their sensitivity to the expected compression of the ISM clouds by the hot wind. Here, we report the first spatially resolved UV emission spectroscopy of a prototypical (radio-quiet) quasar-driven superwind around the obscured quasar SDSS J1356+1026 at z = 0.123. We observe ratios of O VI/C IV, N V/C IV, and C IV/He II that are remarkably similar for outflowing gas clouds ≲100 pc and ≈10 kpc from the nucleus. Such similarity is expected for clouds with AGN radiation-pressure-dominated dynamics. Comparing the observed line emission to models of clouds in balance with radiation pressure and/or a hot wind, we rule out the presence of a dynamically important hot wind and constrain the ratio of hot gas pressure to radiation pressure to Phot/Prad ≲ 0.25 both at ≲100 pc and ≈10 kpc from the nucleus. Moreover, the predictions of the radiation pressure confined cloud models that best fit observed UV line ratios are consistent with the observed diffuse X-ray spectrum. These results indicate that this AGN superwind is driven by radiation pressure or was driven by a hot wind that has since dissipated despite ongoing AGN activity.

Keywords: active galactic nuclei; quasars; galactic winds; supermassive black holes; active galaxies
Discovery of X-Ray Polarization from the Black Hole Transient Swift J1727.8-1613

We report the first detection of the X-ray polarization of the bright transient Swift J1727.8-1613 with the Imaging X-ray Polarimetry Explorer. The observation was performed at the beginning of the 2023 discovery outburst, when the source resided in the bright hard state. We find a time- and energy-averaged polarization degree of 4.1% ± 0.2% and a polarization angle of 2.°2 ± 1.°3 (errors at 68% confidence level; this translates to ~20σ significance of the polarization detection). This finding suggests that the hot corona emitting the bulk of the detected X-rays is elongated, rather than spherical. The X-ray polarization angle is consistent with that found in submillimeter wavelengths. Since the submillimeter polarization was found to be aligned with the jet direction in other X-ray binaries, this indicates that the corona is elongated orthogonal to the jet.

Keywords: accretion; x-ray astronomy; low-mass x-ray binary stars; polarimetry; astrophysical black holes
Modeling and Orbital Parameters of Kepler Heartbeat Stars

Heartbeat stars (HBSs) are astrophysical laboratories for studying binaries with eccentric orbits. A catalog of 173 Kepler HBSs was reported by Kirk et al., and we have modeled 153 of them by using a corrected version of Kumar et al.'s model based on the Markov Chain Monte Carlo method. The orbital parameters, including orbital period, eccentricity, orbital inclination, the argument of periastron, and epoch of the periastron passage of these HBSs, have been determined and are presented. Orbital parameters of more than 100 systems are obtained for the first time. After comparing the parameters of 38 overlapping systems with previous works, it is shown that the orbital parameters of HBSs can be reliably derived using this method. These samples can also be valuable targets for future studies of the structures and evolution of HBSs. The eccentricity-period (e-P) relation also reveals the existence of orbital circularization in HBSs. We then propose an empirical equation for the relationship between the upper limit of eccentricity and the orbital period in systems with orbital periods less than 10 days based on the e-P relation. In addition, it is possible that seven systems in the catalog with eccentricity less than 0.02 should be excluded from the HBS candidates.

Keywords: binary stars; elliptical orbits
Electron Densities of Transition Region Loops Derived from IRIS O IV Spectral Data

Loops are fundamental structures in the magnetized atmosphere of the Sun. Their physical properties are crucial for understanding the nature of the solar atmosphere. Transition region loops are relatively dynamic and their physical properties have not yet been fully understood. With spectral data of the line pair of O IV 1399.8 Å and 1401.2 Å ( ${T}_{\max }=1.4\times {10}^{5}$ K) of 23 transition region loops obtained by IRIS, we carry out the first systematic analyses to their loop lengths (L), electron densities (n e ), and effective temperatures. We found electron densities, loop lengths, and effective temperatures of these loops are in the ranges of 8.9 × 109–3.5 × 1011 cm‑3, 8–30 Mm, and 1.9 × 105–1.3 × 106 K, respectively. At a significant level of 90%, regression analyses show that the relationship between electron densities and loop lengths is n e [cm‑3] ∝ (L[Mm])‑0.78±0.42, while the dependences of electron densities on effective temperatures and that on the line intensities are not obvious. These observations demonstrate that transition region loops are significantly different than their coronal counterparts. Further studies on the theoretical aspect based on the physical parameters obtained here are of significance for understanding the nature of transition region loops.

Keywords: solar coronal loops; solar atmosphere; solar transition region; spectroscopy