Sazuna/UAT_keywords huggingface dataset:
Gravitational Wave Implications for the Parity Symmetry of Gravity in the High Energy Region. Einstein's general relativity, as the most successful theory of gravity, is one of the cornerstones of modern physics. However, the experimental tests for gravity in the high energy region are limited. The emerging gravitational-wave astronomy has opened an avenue for probing the fundamental properties of gravity in a strong and dynamical field, and in particular, a high energy regime. In this work, we test the parity conservation of gravity with gravitational waves. If the parity symmetry is broken, the left- and right-handed modes of gravitational waves would follow different equations of motion, dubbed as birefringence. We perform full Bayesian inference by comparing the state-of-the-art waveform with parity violation with the compact binary coalescence data released by LIGO and Virgo collaboration. We do not find any violations of general relativity, thus constrain the lower bound of the parity-violating energy scale to be 0.09 GeV through the velocity birefringence of gravitational waves. This provides the most stringent experimental test of gravitational parity symmetry to date. We also find third generation gravitational-wave detectors can enhance this bound to ${ \mathcal O }({10}^{2})$ GeV if there is still no violation, comparable to the current energy scale in particle physics, which indicates gravitational-wave astronomy can usher in a new era of testing the ultraviolet behavior of gravity in the high energy region.

Keywords: Gravitational wave astronomy
Growth of Stellar-mass Black Holes in Dense Molecular Clouds and GW190521. A stellar-mass black hole can grow its mass noticeably through Bondi accretion, if it is embedded in an extremely dense and massive molecular cloud with slow motion with respect to the ambient medium for an extended period of time. This provides a novel, yet challenging channel for the formation of massive stellar-mass black holes. We discuss how this channel may account for the massive binary black hole merger system GW190521 as observed by LIGO/Virgo gravitational wave detectors as well as the claimed massive black hole candidate LB-1.

Keywords: Bondi accretion, Black holes, Gravitational waves
Unresolved Multiple Stars and Galactic Clusters' Mass Estimates. If not properly accounted for, unresolved binary stars can induce a bias in the photometric determination of star cluster masses inferred from star counts and the luminosity function. A correction factor close to 1.15 (for a binary fraction of 0.35) was found in Borodina et al., which needs to be applied to blind photometric mass estimates. This value for the correction factor was found to be smaller than literature values. In an attempt to lift this discrepancy, in this work the focus is on higher order multiple stars with the goal of investigating the effect of triple and quadruple systems adopting the same methodology and data set as in the quoted work. The result is that when triple and quadruple, together with binary, systems are properly accounted for, the actual cluster mass (computed as all stars were single) should be incremented by a factor of 1.18-1.27, depending on the cluster and when the binary fraction α is 0.35. Fitting formulae are provided to derive the increment factor for different binary star percentages.

Keywords: Stellar mass functions, Open star clusters, Binary stars
Revisiting the Integrated Star Formation Law. II. Starbursts and the Combined Global Schmidt Law. We compile observations of molecular gas contents and infrared-based star formation rates (SFRs) for 112 circumnuclear star-forming regions, in order to reinvestigate the form of the disk-averaged Schmidt surface density star-formation law in starbursts. We then combine these results with total gas and SFR surface densities for 153 nearby nonstarbursting disk galaxies from de los Reyes &amp; Kennicutt (2019), to investigate the properties of the combined star formation law, following Kennicutt (1998). We confirm that the combined Schmidt law can be fitted with a single power law with slope n = 1.5 ± 0.05 (including fitting method uncertainties), somewhat steeper than the value n = 1.4 ± 0.15 found by Kennicutt. Fitting separate power laws to the nonstarbursting and starburst galaxies, however, produces very different slopes (n = 1.34 ± 0.07 and 0.98 ± 0.07, respectively), with a pronounced offset in the zero-point (∼0.6 dex) of the starburst relation to higher SFR surface densities. This offset is seen even when a common conversion factor between CO intensity and molecular hydrogen surface density is applied, and it is confirmed when disk surface densities of interstellar dust are used as proxies for gas measurements. Tests for possible systematic biases in the starburst data fail to uncover any spurious sources for such a large offset. We tentatively conclude that the global Schmidt law in galaxies, at least as it is conventionally measured, is bimodal or possibly multimodal. Possible causes may include changes in the small-scale structure of the molecular interstellar medium or the stellar initial mass function. A single n ∼ 1.5 power law still remains as a credible approximation or "recipe" for analytical or numerical models of galaxy formation and evolution.

Keywords: Interstellar dust, Starburst galaxies, Blue compact dwarf galaxies, Spiral galaxies, Disk galaxies, Star formation, Galaxy evolution, Interacting galaxies, Luminous infrared galaxies
Mapping the Supernovae Driven Winds of the Large Magellanic Cloud in Hα Emission I. We present the first spectroscopically resolved Hα emission map of the Large Magellanic Cloud's (LMC) galactic wind. By combining new Wisconsin H-alpha Mapper observations (IHα ≳ 10 mR) with existing H I 21 cm emission observations, we (1) mapped the LMC's nearside galactic wind over a local standard of rest (LSR) velocity range of +50 ≤ vLSR ≤ +250 km s-1, (2) determined its morphology and extent, and (3) estimated its mass, outflow rate, and mass-loading factor. We observe Hα emission from this wind to typically 1° off the LMC's H I disk. Kinematically, we find that the diffuse gas in the warm-ionized phase of this wind persists at both low (≲100 km s-1) and high (≳100 km s-1) velocities, relative to the LMC's H I disk. Furthermore, we find that the high-velocity component spatially aligns with the most intense star-forming region, 30 Doradus. We, therefore, conclude that this high-velocity material traces an active outflow. We estimate the mass of the warm (Te ≈ 104 K) ionized phase of the nearside LMC outflow to be $\mathrm{log}\left({M}_{\mathrm{ionized}}/{M}_{\odot }\right)=7.51\pm 0.15$ for the combined low and high-velocity components. Assuming an ionization fraction of 75% and that the wind is symmetrical about the LMC disk, we estimate that its total (neutral and ionized) mass is $\mathrm{log}\left({M}_{\mathrm{total}}/{M}_{\odot }\right)=7.93$ , its mass-flow rate is ${\dot{M}}_{\mathrm{outflow}}\approx 1.43\,{M}_{\odot }\,{\mathrm{yr}}^{-1}$ , and its mass-loading factor is η ≈ 4.54. Our average mass-loading factor results are roughly a factor of 2.5 larger than previous Hα imaging and UV absorption line studies, suggesting that those studies are missing nearly half the gas in the outflows.

Keywords: Galactic winds, Stellar feedback, Dwarf galaxies, High-velocity clouds, Large Magellanic Cloud, Galaxy evolution, Interstellar medium, Circumgalactic medium
Search for Radio Remnants of Nearby Off-axis Gamma-Ray Bursts in a Sample of Swift/BAT Events. The multi-messenger discovery of gravitational waves (GWs) and light from the binary neutron star (NS) merger GW170817, associated with gamma-ray burst (GRB) 170817A and kilonova AT2017gfo, has marked the start of a new era in astrophysics. GW170817 has confirmed that binary NS mergers are progenitors of at least some short GRBs. The peculiar properties of the GRB 170817A radio afterglow, characterized by a delayed onset related to the off-axis geometry, have also demonstrated how some nearby short GRBs may not be identified as such with standard short-timescale electromagnetic follow-up observations. Building upon this new information, we performed late-time radio observations of a sample of four short GRBs with unknown redshift and no previously detected afterglow in the Swift/BAT sample in order to identify nearby ( ${d}_{L}\lesssim 200$ Mpc) off-axis GRB candidates via their potential late-time radio signatures. We find a previously uncatalogued radio source within the error region of GRB 130626 with a $3\mbox{--}6\,\mathrm{GHz}$ flux density consistent with an NS radio flare at a distance of ∼100 Mpc. An origin related to a persistent radio source unrelated to the GRB cannot be excluded nor confirmed given the high chance of false positives in error regions as large as those considered here, and the limited time baseline of our observations. Further radio (and X-ray) follow-up observations are needed to better understand the origin of this source.

Keywords: Radio continuum emission, Non-thermal radiation sources, Gravitational waves, Gamma-ray bursters
Assessment of Cr Isotopic Heterogeneities of Volatile-rich Asteroids Based on Multiple Planet Formation Models. Describing the comprehensive evolutionary scenario for asteroids is key to explaining the various physical processes of the solar system. Bulk-scale carbonaceous chondrites (CCs) possibly record the primordial information associated with the formation processes of their parent bodies. In this study, we tried to estimate the relative formation region of volatile-rich asteroids by utilizing the nucleosynthetic Cr isotopic variation (54Cr/52Cr) in bulk-scale CCs. Numerical calculations were conducted to track the temporal evolution of isotopically different (solar and presolar) dust and 54Cr/52Cr values for mixed materials with disk radius. First, we found that isotopic heterogeneities in CC formation regions were preserved with a weak turbulence setting that increased the timescales of the advection and diffusion in the disk. Second, we assessed the effects of gaps formed by giant planets. Finally, the distance from the injected supernovae and Cr isotopic compositions of the presolar grains were investigated in terms of the estimated formation region of CCs. In our results, a plausible formation region of four types of CCs could be obtained with the supernova from approximately 2 pc and typical Cr isotopic compositions of presolar grains. Among the parent bodies of CCs (i.e., volatile-rich asteroids), B-type asteroids formed in the outermost region, which is inconsistent with the present population, showing that D-type asteroids are generally located beyond most of the C-complex asteroids. Both the initial and present orbits of asteroids might be explained by the scatter attributed to the inward-outward migration of Jupiter and Saturn.

Keywords: Asteroids, Carbonaceous chondrites, Protoplanetary disks, Meteorites, Asteroid belt, Supernovae
A Systematic Study of Gamma-Ray Flares from the Crab Nebula with Fermi-LAT. I. Flare Detection. Significant flares of GeV γ-ray emission from the Crab Nebula were found by AGILE and Fermi-LAT years ago, indicating that extreme particle acceleration and radiation occurs in young pulsar wind nebulae. To enlarge the flare sample and to investigate their statistical properties will be very useful in understanding the nature of the γ-ray flares. In this paper, we investigate the flaring emission from the Crab Nebula with eleven year observations of the Fermi-LAT. We identify 17 significant flares in the light curve of the low-energy (synchrotron) component of the γ-ray emission. The flare rate is about 1.5 per year, without any significant change or clustering during the 11 years of the observation. We detect a special flare with an extremely long duration of nearly one month, that occurred in 2018 October, with synchrotron photons up to energies of about 1 GeV. The synchrotron component could be fitted by a steady power-law (PL) background and a variable flare component with an exponentially cutoff PL spectrum, not only for the individual flare but also for the combined data, which may favor a similar emission mechanism for all flares. However, we do not find a universal relation between the cutoff energy and the energy fluxes of the flares, which may reflect the complicated acceleration and/or cooling processes of the involved particles.

Keywords: Gamma-ray astronomy, Cosmic rays
The First Extensive Exploration of UV-bright Stars in the Globular Cluster NGC 2808. In this study, we identified and characterized the hot and luminous UV-bright stars in the globular cluster NGC 2808. We combined data from the Ultra Violet Imaging Telescope (UVIT) on board the Indian space satellite AstroSat with the Hubble Space Telescope UV Globular Cluster Survey data for the central region (within $\sim 2\buildrel{\,\prime}\over{.} 7\times 2\buildrel{\,\prime}\over{.} 7$ ) and Gaia and ground-based optical photometry for the outer parts of the cluster. We constructed the UV and UV-optical color-magnitude diagrams, compared the horizontal branch (HB) members with the theoretical zero- and terminal-age HB models, and identified 34 UV-bright stars. The spectral energy distributions of the UV-bright stars were fitted with theoretical models to estimate their effective temperatures (12,500-100,000 K), radii (0.13-2.2 R⊙), and luminosities (∼40-3000 L⊙) for the first time. These stars were then placed on the Hertzsprung-Russell diagram, along with theoretical post-HB evolutionary tracks, to assess their evolutionary status. The models suggest that most of these stars are in the asymptotic giant branch (AGB)-manqué phase, and all except three have evolutionary masses &lt;0.53 M⊙. We also calculated the theoretically expected number of hot post-(early)-AGB stars in this cluster and found the range to match our observations. Seven UV-bright stars located in the outer region of the cluster, identified from the AstroSat/UVIT images, are ideal candidates for detailed follow-up spectroscopic studies.

Keywords: Globular star clusters, Horizontal branch stars, Post-asymptotic giant branch stars, Ultraviolet photometry, Hertzsprung Russell diagram
Population Synthesis of Galactic Be-star Binaries with a Helium-star Companion. LB-1 was originally suggested to harbor a very massive (∼70 M⊙) black hole, but was recently suggested to be a post-mass transfer binary containing a Be star and a helium (He) star. In this paper, we use the binary population synthesis method to simulate the potential population of the Be-He binaries in the Milky Way. Mass transfer process during the progenitor binary evolution plays a vital role in determining the possible properties of the Be-He binary population. By constructing a range of physical models with significantly different mass-transfer efficiencies, we obtain the predicted distributions at the current epoch of the component masses and the orbital periods for the Be-He binaries. In particular, we show that, LB-1 very likely has evolved through non-conservative mass transfer if it is indeed a Be-He system. We estimate that there are more than 103 Be-He binaries with V-band apparent magnitudes brighter than LB-1.

Keywords: Close binary stars, Interacting binary stars, Stellar evolution
Evolution of Stellar Feedback in H II Regions. Stellar feedback is needed to produce realistic giant molecular clouds and galaxies in simulations, but due to limited numerical resolution, feedback must be implemented using sub-grid models. Observational work is an important means to test and anchor these models, but limited studies have assessed the relative dynamical role of multiple feedback modes, particularly at the earliest stages of expansion when H II regions are still deeply embedded. In this paper, we use multiwavelength (radio, infrared, and X-ray) data to measure the pressures associated with direct radiation (Pdir), dust-processed radiation (PIR), photoionization heating (PH II), and shock-heating from stellar winds (PX) in a sample of 106 young, resolved H II regions with radii ≲0.5 pc to determine how stellar feedback drives their expansion. We find that the PIR dominates in 84% of the regions and that the median Pdir and PH II are smaller than the median PIR by factors of ≍6 and ≍9, respectively. Based on the radial dependences of the pressure terms, we show that H II regions transition from PIR-dominated to PH II-dominated at radii of ∼3 pc. We find a median trapping factor of ftrap ∼ 8 without any radial dependence for the sample, suggesting this value can be adopted in sub-grid feedback models. Moreover, we show that the total pressure is greater than the gravitational pressure in the majority of our sample, indicating that the feedback is sufficient to expel gas from the regions.

Keywords: Galaxy formation, Compact H II region, Stellar feedback, Star forming regions, Star formation, H II regions
Probing the Hot Circumgalactic Medium with Broad O VI and X-Rays. Most of the baryonic mass in the circumgalactic medium (CGM) of a spiral galaxy is believed to be warm-hot, with temperature around 106 K. The narrow O VI absorption lines probe a somewhat cooler component at $\mathrm{log}\,T({\rm{K}})=5.5$ , but broad O VI absorbers have the potential to probe the hotter CGM. Here we present 376 ks Chandra LETG observations of a carefully selected galaxy in which the presence of broad O VI together with the non-detection of Lyα was indicative of hot gas. The strongest line expected to be present at ≈106 K is O VII λ21.602. There is a hint of an absorption line at the redshifted wavelength, but the line is not detected with better than 2σ significance. A physical model, taking into account strengths of several other lines, provides better constraints. Our best-fit absorber model has $\mathrm{log}\,T({\rm{K}})=6.3\pm 0.2$ and $\mathrm{log}{N}_{{\rm{H}}}({\mathrm{cm}}^{-2})={20.7}_{-0.5}^{+0.3}$ . These parameters are consistent with the hot plasma model based on UV observations; other O VI models of cooler gas phases are ruled out at better than 99% confidence. Thus we have suggestive, but not conclusive evidence for the broad O VI absorber probing the hot gas from the shallow observations of this pilot program. About 800 ks of XMM-Newton observations will detect the expected absorption lines of O VII and O VIII unequivocally. Future missions like XRISM, Arcus, and Athena will revolutionize the CGM science.

Keywords: X-ray astronomy, Galaxy formation, Ultraviolet astronomy, Galaxy evolution, X-ray observatories, Circumgalactic medium, Warm-hot intergalactic medium
DR 21 South Filament: A Parsec-sized Dense Gas Accretion Flow onto the DR 21 Massive Young Cluster. DR 21 south filament (DR21SF) is a unique component of the giant network of filamentary molecular clouds in the north region of the Cygnus X complex. Unlike the highly fragmented and star-forming active environment wherein it resides, DR21SF exhibits a coherent profile in the column density map with very few star formation signposts, even though the previously reported linear density of the filament is an order of magnitude higher than the thermal stable threshold. We derive the size (3.6 pc by 0.13 pc), temperature (10-15 K), and mass (1048 M⊙) of DR21SF from our single-dish observations of NH3 (1, 1) and (2, 2) inversion lines in conjunction with the column density map from our previous work. Star-forming sites are identified along the filament where gas temperature is excessive. We find clear gradients in radial velocity and intrinsic line width along the spine of the filament. The gradients can be well interpreted by a scenario of an accretion flow feeding DR 21 at a mass transfer rate of 1.1 × 10-3M⊙ yr-1. Based on the analysis of its kinematic temperature, intrinsic line width, and mass distribution, we conclude that DR21SF is in an overall trans-critical status, which indicates an early evolutionary stage.

Keywords: Interstellar filaments
Production and Persistence of Extreme Two-temperature Plasmas in Radiative Relativistic Turbulence. Turbulence is a predominant process for energizing electrons and ions in collisionless astrophysical plasmas, and thus is responsible for shaping their radiative signatures (luminosity, spectra, and variability). To better understand the kinetic properties of a collisionless radiative plasma subject to externally driven turbulence, we investigate particle-in-cell simulations of relativistic plasma turbulence with external inverse Compton cooling acting on the electrons. We find that ions continuously heat up while electrons gradually cool down (due to the net effect of radiation), and hence the ion-to-electron temperature ratio Ti/Te grows in time. We show that Ti/Te is limited only by the size and duration of the simulations (reaching ${T}_{i}/{T}_{e}\sim {10}^{3}$ ), indicating that there are no efficient collisionless mechanisms of electron-ion thermal coupling. This result has implications for models of radiatively inefficient accretion flows, such as observed in the Galactic center and in M87, for which so-called two-temperature plasmas with ${T}_{i}/{T}_{e}\gg 1$ have been invoked to explain their low luminosity. Additionally, we find that electrons acquire a quasi-thermal distribution (dictated by the competition of turbulent particle energization and radiative cooling), while ions undergo efficient nonthermal acceleration (acquiring a harder distribution than in equivalent nonradiative simulations). There is a modest nonthermal population of high-energy electrons that are beamed intermittently in space, time, and direction; these beamed electrons may explain rapid flares in certain high-energy astrophysical systems (e.g., in the Galactic center). These numerical results demonstrate that extreme two-temperature plasmas can be produced and maintained by relativistic radiative turbulence.

Keywords: Accretion, High energy astrophysics, Relativistic jets, Plasma astrophysics, Non-thermal radiation sources, Cosmic rays
The Formation of Electron Outflow Jets with Power-law Energy Distribution in Guide-field Magnetic Reconnection. Observationally, electron beams with power-law energy spectra are commonly associated with solar flares. Previous studies have found that during magnetic reconnection with a guide field Bg larger than 0.1 times the asymptotic field B0, electron beams are unable to develop due to the strong deflection caused by the guide field. Using particle-in-cell simulations we show that in force-free reconnection, the development of an electron Kelvin-Helmholz instability can suppress the Hall effect and produce a flute-like outflow exhaust, in which both electrons and ions are nearly frozen-in with the magnetic field. The coupling of a continuously growing electron velocity shear and E × B drift drive the electrons out of magnetic vortices and results in collimated jets with a power-law energy spectrum in the elongated exhaust. The spatial density of electron jets is comparable to the background and is highly inhomogeneous, signifying on asymmetric density structure in guide field reconnection.

Keywords: Solar energetic particles, Solar magnetic reconnection