adsabs/SciX_UAT_keywords huggingface dataset:
Probing the Halo Gas Distribution in the Inner Galaxy with Fermi Bubble Observations

The hot halo gas distribution in the inner Milky Way (MW) contains key fossil records of the past energetic feedback processes in the galactic center. Here, we adopt a variety of spherical and disk-like MW halo gas models as initial conditions in a series of simulations to investigate the formation of the Fermi bubbles in the jet-shock scenario. The simulation results are compared directly with relevant X-ray and gamma-ray observations of the Fermi bubbles to constrain the halo gas distribution in the inner Galaxy before the Fermi bubble event. Our best-fit gas density distribution can be described by a power law in radius ne(r) = 0.01(r/1 kpc)-1.5 cm-3. Our study cannot determine if there is an inner density core, which if exists, should be very small with size rc ≲ 0.5 kpc. When extrapolating to large radii r ~ 50-90 kpc, our derived density distribution lies appreciably below the recently estimated gas densities from ram pressure stripping calculations, suggesting that the halo gas density profile either flattens out or has one or more discontinuities within 10 ≲ r ≲ 50 kpc. Some of these discontinuities may be related to the eROSITA bubbles, and our derived gas density profile may correspond to the hot gas distribution in the inner eROSITA bubbles about 5 Myr ago.

Keywords: galactic center; circumgalactic medium; cosmic rays; gamma-rays; computational methods; galaxy jets; jets; shocks; active galaxies; x-ray astronomy; galactic winds
Kinematic Decomposition of IllustrisTNG Disk Galaxies: Morphology and Relation with Morphological Structures

We recently developed an automated method, auto-GMM, to decompose simulated galaxies. It extracts kinematic structures in an accurate, efficient, and unsupervised way. We use auto-GMM to study the stellar kinematic structures of disk galaxies from the TNG100 run of IllustrisTNG. We identify four to five structures that are commonly present among the diverse galaxy population. Structures having strong to moderate rotation are defined as cold and warm disks, respectively. Spheroidal structures dominated by random motions are classified as bulges or stellar halos, depending on how tightly bound they are. Disky bulges are structures that have moderate rotation but compact morphology. Across all disky galaxies and accounting for the stellar mass within 3 half-mass radii, the kinematic spheroidal structures, obtained by summing up stars of bulges and halos, contribute ∼45% of the total stellar mass, while the disky structures constitute ∼55%. This study also provides important insights into the relationship between kinematically and morphologically derived galactic structures. Comparing the morphology of kinematic structures with that of traditional bulge+disk decomposition, we conclude that (1) the morphologically decomposed bulges are composite structures comprising a slowly rotating bulge, an inner halo, and a disky bulge; (2) kinematically disky bulges, akin to what are commonly called pseudo-bulges in observations, are compact disk-like components that have rotation similar to warm disks; (3) halos contribute almost 30% of the surface density of the outer part of morphological disks when viewed face on; and (4) both cold and warm disks are often truncated in central regions.

Keywords: disk galaxies; galaxy structure; hydrodynamical simulations; galaxy dynamics; galaxy kinematics
LSST Survey Strategies and Brown Dwarf Parallaxes

The Vera C. Rubin Observatory's Legacy Survey of Space and Time (LSST) has the potential to measure parallaxes for thousands of nearby ultracool dwarfs, enabling improved measurements of the brown dwarf luminosity function. We develop a simple model to estimate the number of L dwarfs and T dwarfs with parallaxes with signal-to-noise ratio greater than 10 in the baseline LSST survey. High-quality astrometry imposes scheduling constraints. We assess different possible observing strategies using quantitative metrics and make recommendations as part of the LSST community input process. We find that the new substellar parallax sample will represent a nearly order-of-magnitude increase on existing samples, with ~50-100 objects per spectral type bin for late-L to mid-T dwarfs. The sample size is robust (±5% or less) against most survey strategy changes under consideration, although we do identify areas of tension with other uses of twilight time that could have a larger impact.

Keywords: brown dwarfs; l dwarfs; t dwarfs; sky surveys; parallax
The Equilibrium of Coronal Loops Near Separatrices

We present numerical models from the field-aligned HYDrodynamics and RADiation code (HYDRAD) of a highly asymmetric closed coronal loop with near-singular expansion factor. This loop was chosen to simulate a coronal magnetic flux tube that passes close to a null point, as in the last set of closed loops under the fan surface of a coronal jet or a pseudostreamer. The loop has a very large cross section localized near the coronal null. The coronal heating was assumed to be uniform and steady. A siphon flow establishes itself within 4 hr of simulation time, flowing from the smaller-area footpoint to the larger-area footpoint, with high initial speeds dropping rapidly as the plasma approaches the null region. Observationally, this would translate to strong upflows on the order of 10 km s-1 from the footpoint rooted in the localized minority polarity, and weak downflows from the fan-surface footpoint on the order of a few kilometers per second, along with near-stationary plasma near the null region. We present the model results for two heating rates. In addition, we analyzed analogous Hinode EUV Imaging Spectrometer observations of null-point topologies, which show associated Doppler shifts in the plasma that correlate well with the simulation results in both direction and magnitude of the bulk velocity. We discuss the implications of our results for determining observationally the topology of the coronal magnetic field.

Keywords: quiet solar corona; solar corona; solar coronal heating; solar coronal loops
High-redshift Narrow-line Seyfert 1 Galaxies: A Candidate Sample

The study of narrow-line Seyfert 1 galaxies (NLS1s) is now mostly limited to low redshift (z < 0.8) because their definition requires the presence of the Hβ emission line, which is redshifted out of the spectral coverage of major ground-based spectroscopic surveys at z > 0.8. We studied the correlation between the properties of Hβ and Mg II lines of a large sample of SDSS DR14 quasars to find high-z NLS1 candidates. Based on the strong correlation of FWHM(Mg II) = (0.880 ± 0.005) × FWHM(Hβ) + (0.438 ± 0.018), we present a sample of high-z NLS1 candidates having FWHM of Mg II < 2000 km s-1. The high-z sample contains 2684 NLS1s with redshift z = 0.8-2.5 with a median logarithmic bolometric luminosity of 46.16 ± 0.42 erg s-1, logarithmic black hole mass of 8.01 ± 0.35 M⊙, and logarithmic Eddington ratio of 0.02 ± 0.27. The fraction of radio-detected high-z NLS1s is similar to that of the low-z NLS1s and SDSS DR14 quasars at a similar redshift range, and their radio luminosity is found to be strongly correlated with their black hole mass.

Keywords: quasars; supermassive black holes; spectroscopy
Radio Counterparts of Gamma-Ray Sources in the Cygnus Region

The view of the gamma-ray universe is being continuously expanded by space high-energy (HE) and ground-based very-high-energy (VHE) observatories. Yet, the angular resolution limitation still precludes a straightforward identification of these gamma-ray emitting sources. Radio observations are an effective tool for searching their possible counterparts at lower energies because the same population of relativistic electrons responsible for radio emission can also produce HE/VHE emission via inverse-Compton scattering. The Cygnus region is crowded by many gamma-ray sources, most of them remaining unidentified. In order to find possible counterparts to unidentified gamma-ray sources, we carried out a deep survey of the Cygnus region using the Giant Metrewave Radio Telescope at 610 and 325 MHz. We did a detailed search for counterparts in the error circle of HE/VHE sources. We report 36 radio sources found in the error ellipse of 15 HE sources, and 11 in those of VHE sources. Eight sources have a very steep radio spectral index α < -1.5, these are most likely to be pulsars and will be followed up for a periodicity search. Such a significant number of pulsar candidates within the error circle of HE/VHE sources prompts a fresh look at the energetics and efficacy of pulsars and pulsar wind nebulae in this context.

Keywords: supernova remnants; pulsars; gamma-ray sources; radio continuum emission; catalogs; surveys
Clumping in the Winds of Wolf-Rayet Stars

We attempt to determine the driver for clumping in hot-star winds by extending the measure of the spectral variability level of Galactic Wolf-Rayet stars to by far the hottest known among them, the WN2 star WR 2 and the WO2 stars WR 102 and WR 142. These three stars have T⋆ = 140 and 200 kK, the last two being well above the bulk of WR stars with T⋆ ∼ 40-120 kK. This full temperature range for WR stars is much broader than that of their O-star progenitors (∼30-50 kK), so is better suited to look for any temperature dependence of wind clumping. We have obtained multiple observations with high signal-to-noise, moderate-resolution spectroscopy in search of small-scale variability in the strong emission lines from the dense winds of these three extreme stars, and find a very low-level of variability in both stars. Temperature and terminal velocity are correlated, so faster winds show a lower variability, though this trend goes against any predictions made involving Line Deshadowing Instability (LDI) only, implying that instabilities intrinsic to LDI are not the main source of wind clumping. Instead, it could be taken as support for the suggestion that clumps are caused by a subsurface convection zone (SSCZ) at T ∼ 170 kK, since such an SSCZ would have little opportunity to operate under the hydrostatic surface of these hottest WR stars. It is still possible, however, that an SSCZ-related driver could interact with nonlinear line instability effects to enhance or possibly even produce clumps.

Keywords: wolf-rayet stars; stellar winds; stellar convective zones; radiative transfer
Modeling Gamma-Ray Burst Afterglow Observations with an Off-axis Jet Emission

Gamma-ray bursts (GRBs) are fascinating extragalactic objects. They represent a fantastic opportunity to investigate unique properties not exhibited in other sources. Multiwavelength afterglow observations from some short- and long-duration GRBs reveal an atypical long-lasting emission that evolves differently from the canonical afterglow light curves favoring the off-axis emission. We present an analytical synchrotron afterglow scenario and the hydrodynamical evolution of an off-axis top-hat jet decelerated in a stratified surrounding environment. The analytical synchrotron afterglow model is shown during the coasting, deceleration (off- and on-axis emission), and post-jet break decay phases, and the hydrodynamical evolution is computed by numerical simulations showing the time evolution of the Doppler factor, the half-opening angle, the bulk Lorentz factor, and the deceleration radius. We show that numerical simulations are in good agreement with those derived with our analytical approach. We apply the current synchrotron model and successfully describe the delayed nonthermal emission observed in a sample of long and short GRBs with evidence of off-axis emission. Furthermore, we provide constraints on the possible afterglow emission by requiring the multiwavelength upper limits derived for the closest Swift-detected GRBs and promising gravitational-wave events.

Keywords: gamma-ray bursts; non-thermal radiation sources; interstellar medium
Ultrafast Variability in AGN Jets: Intermittency and Lighthouse Effect

Gamma-ray flares from active galactic nuclei (AGNs) show substantial variability on ultrafast timescales (i.e., shorter than the light-crossing time of the AGN's supermassive black hole). We propose that ultrafast variability is a by-product of the turbulent dissipation of the jet Poynting flux. Due to the intermittency of the turbulent cascade, the dissipation is concentrated in a set of reconnecting current sheets. Electrons energized by reconnection have a strong pitch-angle anisotropy, i.e., their velocity is nearly aligned with the guide magnetic field. Then each current sheet produces a narrow radiation beam, which dominates the emission from the whole jet when it is directed toward the observer. The ultrafast variability is set by the light-crossing time of a single current sheet, which is much shorter than the light-crossing time of the whole emission region. The predictions of our model are (i) the bolometric luminosity of ultrafast AGN flares is dominated by the inverse Compton (IC) emission as the lower-energy synchrotron emission is suppressed due to the pitch-angle anisotropy; (ii) if the observed luminosity includes a nonflaring component, the variations of the synchrotron luminosity have a small amplitude; and (iii) the synchrotron and IC emission are less variable at lower frequencies, as the cooling time of the radiating particles exceeds the light-crossing time of the current sheet. Simultaneous multiwavelength observations of ultrafast AGN flares can test these predictions.

Keywords: galaxy jets; blazars; gamma-rays
Measuring Fiber Positioning Accuracy and Throughput with Fiber Dithering for the Dark Energy Spectroscopic Instrument

Highly multiplexed, fiber-fed spectroscopy is enabling surveys of millions of stars and galaxies. The performance of these surveys depends on accurately positioning fibers in the focal plane to capture target light. We describe a technique to measure the positioning accuracy of fibers by dithering fibers slightly around their ideal locations. This approach also enables measurement of the total system throughput and point-spread function delivered to the focal plane. We then apply this technique to observations from the Dark Energy Survey Instrument (DESI), and demonstrate that DESI positions fibers to within 0.″08 of their targets (5% of a fiber diameter) and achieves a system throughput within about 7% of expectations.

Keywords: spectroscopy
The Early Data Release of the Dark Energy Spectroscopic Instrument

The Dark Energy Spectroscopic Instrument (DESI) completed its 5 month Survey Validation in 2021 May. Spectra of stellar and extragalactic targets from Survey Validation constitute the first major data sample from the DESI survey. This paper describes the public release of those spectra, the catalogs of derived properties, and the intermediate data products. In total, the public release includes good-quality spectral information from 466,447 objects targeted as part of the Milky Way Survey, 428,758 as part of the Bright Galaxy Survey, 227,318 as part of the Luminous Red Galaxy sample, 437,664 as part of the Emission Line Galaxy sample, and 76,079 as part of the Quasar sample. In addition, the release includes spectral information from 137,148 objects that expand the scope beyond the primary samples as part of a series of secondary programs. Here, we describe the spectral data, data quality, data products, Large-Scale Structure science catalogs, access to the data, and references that provide relevant background to using these spectra.

Keywords: astronomy data reduction; observational cosmology; astronomy databases; astronomy data analysis; astronomy software; surveys; redshift surveys
HST/COS Observations of Quasar Outflows in the 500-1050 Å Rest Frame. VI. Wide, Energetic Outflows in SDSS J0755+2306

We present the analysis of two outflows (S1 at -5500 km s-1 and S2 at -9700 km s-1) seen in recent Hubble Space Telescope/Cosmic Origins Spectrograph observations of quasar SDSS J0755+2306 (z = 0.854). The outflows are detected as absorption troughs from both high-ionization species, including N III, O III, and S IV, and very high-ionization species, including Ar VIII, Ne VIII, and Na IX. The derived photoionization solutions show that each outflow requires a two ionization-phase solution. For S1, troughs from S IV* and S IV allow us to derive an electron number density, ne = 1.8 × 104 cm-3, and its distance from the central source of R = 270 pc. For S2, troughs from O III* and O III yield ne = 1.2 × 103 cm-3 and R = 1600 pc. The kinetic luminosity of S2 is >12% of the Eddington luminosity for the quasar and, therefore, can provide strong AGN feedback effects. Comparison of absorption troughs from O III and O VI in both outflow systems supports the idea that for a given element, higher-ionization ions have larger covering fractions than lower-ionization ones.

Keywords: quasar absorption line spectroscopy; quasars; active galactic nuclei; broad-absorption line quasar
Star Formation and Evolution of Blister-type H II Region Sh2-112

We report the observational findings of the Sh2-112 H II region by using the multiwavelength data analysis ranging from optical to radio wavelengths. This region is powered by the massive O8V-type star BD +45 3216. The surface density distribution and minimum spanning tree analyses of the young stellar object (YSO) candidates in the region reveal their groupings toward the western periphery of the H II region. A GMRT radio continuum emission peak is found toward the northwest boundary of the H II region and is investigated as a compact/ultracompact H II region candidate powered by a B0-B0.5-type star. Toward the southwest direction, a prominent curved rim-like structure is found in the Hα image and GMRT radio continuum maps, where the H2 and 13CO emission is also observed. These results suggest the existence of the ionized boundary layer (IBL) on the surface of the molecular cloud. This IBL is found to be overpressured with respect to the internal pressure of the surrounding molecular cloud. This implies that the shocks are propagating/propagated into the molecular cloud, and the young stars identified within it are likely triggered due to the massive star. It is also found that this region is ionization-bounded toward the west and density-bounded toward the east. Based on the distribution of the ionized gas, molecular material, and YSO candidates, we propose that the Sh2-112 H II region is a good candidate for the blister-type H II region that has been evolved on the surface of a cylindrical molecular cloud.

Keywords: star formation; h ii regions; young stellar objects
Universal Properties of Dense Clumps in Magnetized Molecular Clouds Formed through Shock Compression of Two-phase Atomic Gases

We investigate the formation of molecular clouds from atomic gas by using three-dimensional magnetohydrodynamical simulations, including nonequilibrium chemical reactions, heating/cooling processes, and self-gravity by changing the collision speed V 0 and the angle θ between the magnetic field and colliding flow. We found that the efficiency of the dense-gas formation depends on θ. For small θ, anisotropic super-Alfvénic turbulence delays the formation of gravitationally unstable clumps. An increase in θ develops shock-amplified magnetic fields along which the gas accumulates, creating prominent filamentary structures. We further investigate the statistical properties of dense clumps identified with different density thresholds. The statistical properties of the dense clumps with lower densities depend on V 0 and θ because their properties are inherited from the global turbulence structure of molecular clouds. By contrast, denser clumps appear to have asymptotic universal statistical properties, which do not significantly depend on the properties of the colliding flow. The internal velocity dispersions approach subsonic and plasma β becomes order of unity. We develop an analytic formula of the virial parameter that reproduces the simulation results reasonably well. This property may be one of the reasons for the universality of the initial mass function of stars.

Keywords: molecular clouds; interstellar magnetic fields; interstellar molecules; star formation; interstellar atomic gas
No Dispersed Single Radio Pulses Detected in Archival Parkes Pulsar Observations Targeting Supernova Remnants and Anomalous X-Ray Pulsars

Four supernova remnants and four anomalous X-ray pulsars were previously observed with the Parkes telescope in a campaign to detect pulsed radio emission from associated neutron stars. No signals were detected in the original searches of these data. I have reprocessed the data with the more recently developed HEIMDALL and FETCH software packages, which are optimized for single-pulse detection and classification. In this new analysis, no astrophysical pulses were detected having a signal-to-noise ratio above 7 from any of the targets at dispersion measures ranging from 0 to 104 pc cm-3. I include calculated fluence limits on single radio pulses from these targets.

Keywords: pulsars; transient sources
The Evolution of the Orbital Lightcurve of Hercules X-1 with 35 Day Phase

Hercules X-1/HZ Hercules (Her X-1/HZ Her) is an X-ray binary monitored by multiple X-ray missions since the last century. With the abundance of long-term observations, we present a complete set of orbital lightcurves of Her X-1/HZ Her during the six states of the 35 day cycle in multiple energy bands. These illustrate in detail the changing lightcurve caused by the rotating twisted-tilted accretion disk surrounding the neutron star. The orbital lightcurves during the main high state are analyzed in 0.05 35 day phase intervals. These show the regular occurrence of pre-eclipse dips that march to earlier orbital phases as the 35 day phases increase. From the multiband lightcurves, we derive the time-average orbital phase dependence of column density for photoelectric absorption and energy-independent transmission as a function of 35 day phase. The X-ray lightcurves during low states are similar in shape to the optical low-state lightcurve, but X-ray leads optical by ≃0.04-0.08 in orbital phase.

Keywords: x-ray binary stars; light curves; accretion; neutron stars
Investigating the Nature of MGRO J1908+06 with Multiwavelength Observations

The unidentified TeV source MGRO J1908+06, with emission extending from hundreds of GeV to beyond 100 TeV, is one of the most intriguing sources in the Galactic plane. MGRO J1908+06 spatially associates with an IceCube hotspot of neutrino emission. Although the hotspot is not significant yet, this suggests a possible hadronic origin of the observed gamma-ray radiation. Here we describe a multiwavelength analysis on MGRO J1908+06 to determine its nature. We identify, for the first time, an extended GeV source as the counterpart of MGRO J1908 + 06, discovering possibly associated molecular clouds (MCs). The GeV spectrum shows two well-differentiated components: a soft spectral component below ∼10 GeV, and a hard one (Γ ∼ 1.6) above these energies. The lower-energy part is likely associated with the dense MCs surrounding the supernova remnant (SNR) G40.5-0.5, whereas the higher-energy component, which connects smoothly with the spectrum observed in TeV range, resembles the inverse Compton emission observed in relic pulsar wind nebulae. This simple scenario seems to describe the data satisfactorily, but raises questions about the interpretation of the emission at hundreds of TeV. In this scenario, no detectable neutrino flux would be expected.

Keywords: gamma-ray astronomy; gamma-ray sources; molecular clouds; supernova remnants; rotation powered pulsars