Sazuna/UAT_keywords huggingface dataset:
Long-term Evolution of the Short-term X-Ray Variability of the Jetted TDE Swift J1644+57. The short-term X-ray variability of tidal disruption events (TDEs) and its similarities with that of active galactic nuclei are poorly understood. In this work, we show the diversity of TDEs' short-term X-ray variability, and take Swift J1644+57 as an example to study the evolution of various properties related to the short-term X-ray variability, such as the X-ray flux distribution, power spectral density (PSD), rms variability, time lag, and coherence spectra. We find that the flux distribution of Swift J1644+57 has a lognormal form in the normal state, but deviates from it significantly in the dipping state, thereby implying different physical mechanisms in the two states. We also find that during the first two XMM-Newton observations in the dipping state, Swift J1644+57 exhibited different variability patterns, which are characterized by steeper PSDs and larger rms than the normal state. A significant soft X-ray lag is detected in these two observations, which is ~50 s between 0.3-1 keV and 2-10 keV with a high coherence. Using the 2-10 keV rms of 0.10-0.50, the black hole mass of Swift J1644+57 is estimated to be (0.6\mbox{--}7.9)\times {10}^{6}{M}_{\odot }$ , but the variation of rms as the TDE evolves introduces a large uncertainty. Finally, we discuss the value of conducting similar studies on other TDEs, especially in the coming era of time-domain astronomy when a lot more TDEs will be discovered in X-rays promptly. This also heralds a significant increase in the demand for deep follow-up observations of X-ray selected TDEs with X-ray telescopes of large effective areas and long orbital periods.

Keywords: Accretion, Supermassive black holes, Tidal disruption, Relativistic jets, X-ray transient sources
Orbital Dynamics in a Triaxial Barred Galaxy Model. I. The 2D System. We present the planar orbital dynamics of a realistic barred galaxy model, containing a nucleus (bulge), a triaxial bar, and a disk. After conducting a systematic and exhaustive orbit classification, we manage to determine how the dynamical parameters associated with the bar (mass, semiaxes, and angular velocity) affect the nature of the trajectories of the test particle. In our analysis, we distinguish not only between ordered, chaotic, and escaping motions but also between different types of regular orbits. More specifically, we reveal how the main types of regular orbits are influenced by the changes in the parameters of the galactic bar. Of particular interest is the phenomenon of trapped chaos that occurs in this galaxy model.

Keywords: Galaxy physics, Galaxy structure, Galactic bulge
The Physics of the Coronal-line Region for Galaxies in Mapping Galaxies at Apache Point Observatory. The fundamental nature and extent of the coronal-line region (CLR), which may serve as a vital tracer for active galactic nucleus (AGN) activity, remain unresolved. Previous studies suggest that the CLR is produced by AGN-driven outflows and occupies a distinct region between the broad-line region and the narrow-line region, which places it tens to hundreds of parsecs from the galactic center. Here, we investigate 10 coronal line (CL; ionization potential ≳100 eV) emitting galaxies from the Sloan Digital Sky Survey IV Mapping Galaxies at Apache Point Observatory (MaNGA) catalog with emission from one or more CLs detected at ≥5σ above the continuum in at least 10 spaxels-the largest such MaNGA catalog. We find that the CLR is far more extended, reaching out to 1.3-23 kpc from the galactic center. We crossmatch our sample of 10 CL galaxies with the largest existing MaNGA AGN catalog and identify seven in it; two of the remaining three are galaxy mergers and the final one is an AGN candidate. Further, we measure the average CLR electron temperatures as ranging between 12,331 and 22,530 K, slightly above the typical threshold for pure AGN photoionization (~20,000 K) and indicative of shocks (e.g., merger induced or from supernova remnants) in the CLR. We reason that ionizing photons emitted by the central continuum source (i.e., AGN photoionization) primarily generate the CLs, and that energetic shocks are an additional ionization mechanism that likely produce the most extended CLRs we measure.

Keywords: Photoionization, Active galactic nuclei, Emission line galaxies
NGC 147 Corroborates the Break in the Stellar Mass-Stellar Metallicity Relation for Galaxies. The stellar mass-stellar metallicity relation (MZR) is an essential approach to probing the chemical evolution of galaxies. It reflects the balance between galactic feedback and gravitational potential as a function of stellar mass. However, the current MZR of local dwarf satellite galaxies (M* ≲ 108 M☉; measured from resolved stellar spectroscopy) may not be reconcilable with that of more massive galaxies (M* ≳ 109.5 M☉; measured from integrated-light spectroscopy). Such a discrepancy may result from a systematic difference between the two methods, or it may indicate a break in the MZR around 109 M☉. To address this question, we measured the stellar metallicity of NGC 147 from integrated light using the Palomar Cosmic Web Imager. We compared the stellar metallicity estimates from integrated light with measurements from resolved stellar spectroscopy and found them to be consistent within 0.1 dex. On the other hand, the high-mass MZR overpredicts the metallicity by 0.6 dex at the mass of NGC 147. Therefore, our results tentatively suggest that the discrepancy between the low-mass MZR and high-mass MZR should not be attributed to a systematic difference in techniques. Instead, real physical processes cause the transition in the MZR. In addition, we discovered a positive age gradient in the innermost region and a negative metallicity gradient from the resolved stars at larger radii, suggesting a possible outside-in formation of NGC 147.

Keywords: Local Group, Stellar abundances, Chemical abundances, Dwarf elliptical galaxies, Galaxy abundances, Metallicity
New Hydrodynamic Solutions for Line-driven Winds of Hot Massive Stars Using the Lambert W-function. Hot massive stars present strong stellar winds that are driven by absorption, scattering, and reemission of photons by the ions of the atmosphere (line-driven winds). A better comprehension of this phenomenon, and a more accurate calculation of hydrodynamics and radiative acceleration, is Required to reduce the number of free parameters in spectral fitting and to determine accurate wind parameters such as mass-loss rates and velocity profiles. We use the non-LTE model-atmosphere code CMFGEN to numerically solve the radiative transfer equation in the stellar atmosphere and to calculate the radiative acceleration grad(r). Under the assumption that the radiative acceleration depends only on the radial coordinate, we solve analytically the equation of motion by means of the Lambert W-function. An iterative procedure between the solution of the radiative transfer and the equation of motion is executed in order to obtain a final self-consistent velocity field that is no longer based on any β-law. We apply the Lambert-procedure to three O supergiant stars (ζ Puppis, HD 165763, and α Cam) and discuss the Lambert solutions for the velocity profiles. It is found that, even without recalculation of the mass-loss rate, the Lambert-procedure allows the calculation of consistent velocity profiles that reduce the number of free parameters when a spectral fitting using CMFGEN is performed. Synthetic spectra calculated from our Lambert solutions show significant differences compared to the initial β-law CMFGEN models. The results indicate the importance of consistent velocity profile calculation in the CMFGEN code and its use in a fitting procedure and interpretation of observed spectra.

Keywords: Early-type stars, O stars, Hydrodynamics, Stellar winds, Radiative transfer, Stellar atmospheres
Predicting the Magnetic Fields of a Stealth CME Detected by Parker Solar Probe at 0.5 au. Stealth coronal mass ejections (CMEs) are eruptions from the Sun that are not associated with appreciable low-coronal signatures. Because they often cannot be linked to a well-defined source region on the Sun, analysis of their initial magnetic configuration and eruption dynamics is particularly problematic. In this article, we address this issue by undertaking the first attempt at predicting the magnetic fields of a stealth CME that erupted in 2020 June from the Earth-facing Sun. We estimate its source region with the aid of off-limb observations from a secondary viewpoint and photospheric magnetic field extrapolations. We then employ the Open Solar Physics Rapid Ensemble Information modeling suite to evaluate its early evolution and forward model its magnetic fields up to Parker Solar Probe, which detected the CME in situ at a heliocentric distance of 0.5 au. We compare our hindcast prediction with in situ measurements and a set of flux-rope reconstructions, obtaining encouraging agreement on arrival time, spacecraft-crossing location, and magnetic field profiles. This work represents a first step toward reliable understanding and forecasting of the magnetic configuration of stealth CMEs and slow streamer-blowout events.

Keywords: Solar corona, Solar coronal streamers, Interplanetary magnetic fields, Solar coronal mass ejections
The Mass Budgets and Spatial Scales of Exoplanet Systems and Protoplanetary Disks. Planets are born from disks of gas and dust, and observations of protoplanetary disks are used to constrain the initial conditions of planet formation. However, dust mass measurements of Class II disks with ALMA have called into question whether they contain enough solids to build the exoplanets that have been detected to date. In this paper, we calculate the mass and spatial scale of solid material around Sun-like stars probed by transit and radial velocity exoplanet surveys and compare those to the observed dust masses and sizes of Class II disks in the same stellar-mass regime. We show that the apparent mass discrepancy disappears when accounting for observational selection and detection biases. We find a discrepancy only when the planet formation efficiency is below 100%, or if there is a population of undetected exoplanets that significantly contributes to the mass in solids. We identify a positive correlation between the masses of planetary systems and their respective orbital periods, which is consistent with the trend between the masses and the outer radii of Class II dust disks. This implies that, despite a factor 100 difference in spatial scale, the properties of protoplanetary disks seem to be imprinted on the exoplanet population.

Keywords: Exoplanets, Planetary system formation, Protoplanetary disks, Exoplanet formation, Planet formation
Population Synthesis of Neutron Star X-Ray Binaries Associated with Supernova Remnants. Neutron star X-ray binaries (NS XRBs) associated with supernova remnants (SNRs) are youngest X-ray binaries that can provide insights into the early evolution of X-ray binaries and formation properties of neutron stars. There are an increasing number of NS XRBs that have been discovered within SNRs in our own and nearby galaxies. In this work, we perform binary population synthesis calculations to simulate the population of NS XRBs associated with SNRs for different types of companions, including Roche-lobe-overfilling main-sequence stars, Be stars, and supergiants. We estimate their birth rates and present the distributions of orbital parameters and companion mass for each type of companion. Our calculations show that the majority of the companions are Be X-ray binaries (BeXRBs) and that a few BeXRBs are expected to be associated with SNRs in a Milky Way-type galaxy.

Keywords: Supernova remnants, Neutron stars, X-ray binary stars
Identifying AGN Host Galaxies by Machine Learning with HSC+WISE. We investigate the performance of machine-learning techniques in classifying active galactic nuclei (AGNs), including X-ray-selected AGNs (XAGNs), infrared-selected AGNs (IRAGNs), and radio-selected AGNs (RAGNs). Using the known physical parameters in the Cosmic Evolution Survey (COSMOS) field, we are able to create quality training samples in the region of the Hyper Suprime-Cam (HSC) survey. We compare several Python packages (e.g., scikit-learn, Keras, and XGBoost) and use XGBoost to identify AGNs and show the performance (e.g., accuracy, precision, recall, F1 score, and AUROC). Our results indicate that the performance is high for bright XAGN and IRAGN host galaxies. The combination of the HSC (optical) information with the Wide-field Infrared Survey Explorer band 1 and band 2 (near-infrared) information performs well to identify AGN hosts. For both type 1 (broad-line) XAGNs and type 1 (unobscured) IRAGNs, the performance is very good by using optical-to-infrared information. These results can apply to the five-band data from the wide regions of the HSC survey and future all-sky surveys.

Keywords: Surveys, Active galaxies, Astronomy data analysis, Galaxies
Variations of the Martian Thermospheric Gravity-wave Activity during the Recent Solar Minimum as Observed by MAVEN. Atmospheric gravity (buoyancy) waves (GWs) are of great importance for the energy and momentum budget of all planetary atmospheres. Propagating upward waves carry energy and momentum from the lower atmosphere to thermospheric altitudes and re-distribute them there. On Mars, GWs dominate the variability of the thermosphere and ionosphere. We provide a comprehensive climatology of Martian thermospheric GW activity at solar minimum (end of solar cycle 24) inferred from measurements by the Neutral Gas and Ions Mass Spectrometer on board the Mars Atmosphere and Volatile EvolutioN. The results are compared and interpreted using a one-dimensional spectral nonlinear GW model. Monthly mean GW activity varies strongly as a function of altitude (150-230 km) between 6% and 25%, reaching a maximum at ~170 km. GW activity systematically exhibits a local time variability with nighttime values exceeding those during daytime, in accordance with previous studies. The analysis suggests that the day-night difference is primarily caused by a competition between dissipation due to molecular diffusion and wave growth due to decreasing background density. Thus, the convective instability mechanism is likely to play a less important role in limiting GW amplitudes in the upper thermosphere, which explains their local time behavior.

Keywords: Solar cycle, Internal waves, Mars, Quiet sun, Solar system terrestrial planets, Thermosphere, Remote sensing, Planetary science, Solar activity
The Substructures in Disks Undergoing Vertical Shear Instability. II. Observational Predictions for the Dust Continuum. High-angular resolution observations at submillimeter/millimeter wavelengths of disks surrounding young stars have shown that their morphology is made of azimuthally symmetric or point-symmetric substructures, in some cases with spiral arms or localized spur- or crescent-shaped features. The majority of theoretical studies with the aim of interpreting the observational results have focused on disk models with planets under the assumption that the disk substructures are due to disk-planet interaction. However, so far, only in very few cases have exoplanets been detected in these systems. Furthermore, some substructures are expected to appear before planets form, as they are necessary to drive the concentration of small solids which can lead to the formation of planetesimals. In this work we present observational predictions from high-resolution 3D radiative hydrodynamical models that follow the evolution of gas and solids in a prototoplanetary disk. We focus on substructures in the distribution of millimeter-sized and smaller solid particles produced by the vertical shear instability. We show that their characteristics are compatible with some of the shallow gaps detected in recent observations at sub-mm/mm wavelengths and present predictions for future observations with better sensitivity and angular resolution with ALMA and a Next Generation Very Large Array.

Keywords: Protoplanetary disks
Multi-scale Dust Polarization and Spiral-like Stokes-I Residual in the Class I Protostellar System TMC-1A. We have observed the Class I protostar TMC-1A in the Taurus molecular cloud using the Submillimeter Array (SMA) and the Atacama Large Millimeter/submillimeter Array (ALMA) in the linearly polarized 1.3 mm continuum emission at angular resolutions of ~3″ and ~0.3″, respectively. The ALMA observations also include CO, 13CO, and C18O J = 2-1 spectral lines. The SMA observations trace magnetic fields on the 1000 au scale, the directions of which are neither parallel nor perpendicular to the outflow direction. Applying the Davis-Chandrasekhar-Fermi method to the SMA polarization angle dispersion, we estimate a field strength in the TMC-1A envelope of 1-5 mG. It is consistent with the field strength needed to reduce the radial infall velocity to the observed value, which is substantially less than the local freefall velocity. The ALMA polarization observations consist of two distinct components-a central component and a north/south component. The central component shows polarization directions in the disk minor axis to be azimuthal, suggesting dust self-scattering in the TMC-1A disk. The north/south component is located along the outflow axis and the polarization directions are aligned with the outflow direction. We discuss possible origins of this polarization structure, including grain alignment by a toroidal magnetic field and mechanical alignment by the gaseous outflow. In addition, we discover a spiral-like residual in the total intensity (Stokes I) for the first time. The C18O emission suggests that material in the spiral-like structure is infalling at a speed that is 20% of the local Keplerian speed.

Keywords: Protostars, Polarimetry, Low mass stars, Circumstellar disks
The Intrinsic Shapes of Low Surface Brightness Galaxies (LSBGs): A Discriminant of LSBG Galaxy Formation Mechanisms. We use the low surface brightness galaxy (LSBG) samples created from the Hyper Suprime-Cam Subaru Strategic Program (781 galaxies), the Dark Energy Survey (20977 galaxies), and the Legacy Survey (selected via H I detection in the Arecibo Legacy Fast ALFA Survey, 188 galaxies) to infer the intrinsic shape distribution of the LSBG population. To take into account the effect of the surface brightness cuts employed when constructing LSBG samples, we simultaneously model both the projected ellipticity and the apparent surface brightness in our shape inference. We find that the LSBG samples are well characterized by oblate spheroids, with no significant difference between red and blue LSBGs. This inferred shape distribution is in good agreement with similar inferences made for ultra-diffuse cluster galaxy samples, indicating that environment does not play a key role in determining the intrinsic shape of LSBGs. We also find some evidence that LSBGs are more thickened than similarly massive high surface brightness dwarfs. We compare our results to intrinsic shape measures from contemporary cosmological simulations, and find that the observed LSBG intrinsic shapes place considerable constraints on the formation path of such galaxies. In particular, LSBG production via the migration of star formation to large radii produces intrinsic shapes in good agreement with our observational findings.

Keywords: Observational astronomy, Galaxy structure, Dwarf galaxies, Astronomical methods, Low surface brightness galaxies
Rapid Radical-Radical Induced Explosive Desorption of Ice-coated Interstellar Nanoparticles. The observation of complex organic molecules (COMs) in the gas phase of cold molecular clouds has coined a freeze-out paradox in astrophysics: COMs should be accreted on low-temperature interstellar grains, but not observable in cold molecular clouds. Still, validated mechanisms transporting molecules from the grains back into the gas phase are still elusive, but critical for our understanding of the chemical evolution of the molecular universe. Here we report on the first characterization of rapid radical reactions involving methyl (CH3) and formyl (HCO) radicals in interstellar analogous ices of methane (CH4) and carbon monoxide (CO) upon exposure to proxies of galactic cosmic rays. Rapid radical chain reactions and explosive desorption occurred once the accumulated radicals surpassed critical concentrations of about 1% in the ices at temperatures of cold molecular clouds (5-10 K). These processes may explain the ejection and observation of COMs in the gas phase of cold molecular clouds and potentially rapid outbursts of comets.

Keywords: Interstellar molecules, Radical-radical recombination, Laboratory astrophysics, Astrochemistry
The Galaxy Environment of Extremely Massive Quasars. I. An Overdensity of Hα Emitters at z = 1.47. We measure a strong excess in the galaxy number density around PG 1630+377, an extremely massive (MBH ≃ 109.7M⊙) quasar at z = 1.475, using near-infrared narrowband imaging. We identify 79 narrow H-band excess objects in a 525 arcmin2 area including the vicinity and surroundings of the quasar. These sources are likely Hα line emitting, star-forming galaxies at z ≈ 1.47. We detect a δ = 6.6 ± 2.7 overdensity of narrow H-band excess objects located at a projected distance ≈2.1 Mpc northeast of the quasar, which is the densest region in the target area. The overdensity is present in BzK color-selected galaxies, while a previously reported overdensity in the immediate vicinity of PG 1630+377 is not, and yet appears as a group-like structure. These megaparsec-scale environments are estimated to merge into a ≃1014.7M⊙ cluster at present. Our results support the view that extremely massive black holes form and grow in group-scale environments and later incorporate into a galaxy cluster.

Keywords: Supermassive black holes, Protoclusters, Galaxy groups, Quasars
Could the Local Cavity be an Irregularly Shaped Strömgren Sphere?. Extending for 50-200 pc in all directions from the Sun, the Local Cavity has been characterized as an old supernova bubble consisting of low-density million-degree plasma heated by supernova shocks. We summarize the arguments for and against this model and conclude that hydrogen in the Local Cavity is fully ionized, and the plasma near the Galactic plane is mostly warm (10,000-20,000 K) rather than hot (106 K). The brightest extreme-ultraviolet source detected in the EUVE all-sky survey is the star ϵ CMa. Its EUV radiation photoionizes the outer layers of the Local Interstellar Cloud and other nearby warm interstellar clouds despite the star's 124 pc distance. Pulsar dispersion measures indicate an electron density of 0.012 cm-3 in the Local Cavity itself. At this density the Strömgren sphere of ϵ CMa is as large as the Local Cavity. We propose that the Local Cavity is an irregularly shaped Strömgren sphere containing a small percentage of hot gas likely in many filamentary structures. We also propose that shocks from recent supernovae encountered pre-existing Strömgren sphere gas, and that the partially ionized Local Interstellar Cloud and other nearby clouds could have been formed when supernova shocks encountered regions with relatively weak magnetic fields producing compression, higher density, and recombining hydrogen. * Based on observations made with the NASA/ESA Hubble Space Telescope obtained from the Data Archive at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS AR-09525.01A. These observations are associated with programs #12475, 12596.

Keywords: Ultraviolet sources, Interstellar dynamics, Strömgren spheres, Interstellar magnetic fields, Supernova remnants, Interstellar medium, Diffuse x-ray background