adsabs/SciX_UAT_keywords huggingface dataset:
Accretion onto Stars in the Disks of Active Galactic Nuclei

Disks of gas accreting onto supermassive black holes are thought to power active galactic nuclei (AGN). Stars may form in gravitationally unstable regions of these disks, or may be captured from nuclear star clusters. Because of the dense gas environment, the evolution of these embedded stars can diverge dramatically from those in the interstellar medium. This work extends previous studies of stellar evolution in AGN disks by exploring a variety of ways in which accretion onto stars in AGN disks may differ from Bondi accretion. We find that tidal effects from the supermassive black hole significantly alter the evolution of stars in AGN disks, and that our results do not depend critically on assumptions about radiative feedback on the accretion stream. Thus, in addition to depending on the ambient density and sound speed, the fate of stars in AGN disks depends sensitively on the distance to and mass of the supermassive black hole. This affects the location in the disk in which stellar explosions occur, where compact remnants form and potentially merge to produce gravitational waves, and where different types of chemical enrichment take place.

Keywords: stellar physics; stellar evolutionary models; quasars; galactic center
Prompt Emission of High-energy Nonthermal Photons from a Radiation-dominated Relativistic Magnetic Reconnection

In astrophysics, relativistic magnetic reconnection, where particles can accelerate in a region of a strong electric field and weak magnetic field, is a key physical process for the explanation of high-energy photon synchrotron emission above 160 MeV, the limit given by the balance between the accelerating electric force and the radiation reaction force. However, the reconnection dynamics-more importantly, the particle acceleration and photon emission dynamics-in this radiation-dominated, relativistic regime have not been self-consistently investigated yet. In this paper, through theoretical derivation of the modified relativistic tearing instability (RTI) and kinetic particle-in-cell simulations, we find that, because of the radiation reaction, the compression of the reconnecting current sheet is significantly enhanced, leading to an increase in the RTI growth rate in the short-wavelength range. As a result, during reconnection, the current sheet is fragmented into a chain of many more magnetic null points separated by much smaller plasmoids, which eventually gives rise to significant improvement of particle acceleration efficiency and shortening of photon emission duration. In the simulations, prompt emission at duration ωpeΔT ≃ 233 (reduced by a factor of 3) of high-energy nonthermal photons with a hard power law of index 2.11 for photon energies <100 MeV and index 1.39 for those >100 MeV is observed. These characteristics are consistent with the observed emission properties of short gamma-ray bursts, particularly of GRB 090510, supporting the radiation-dominated reconnection scenario.

Keywords: plasma astrophysics; gamma-ray bursts; magnetic fields; non-thermal radiation sources; high energy astrophysics
The Massive and Distant Clusters of WISE Survey. IX. High Radio Activity in a Merging Cluster

We present a multiwavelength investigation of the radio galaxy population in the galaxy cluster MOO J1506+5137 at z = 1.09 ± 0.03, which in previous work we identified as having multiple complex radio sources. The combined data set used in this work includes data from the Low-Frequency Array Two-meter Sky Survey, NSF's Karl G. Jansky Very Large Array, the Robert C. Byrd Green Bank Telescope, the Spitzer Space Telescope, and the Dark Energy Camera Legacy Survey. We find that there are five radio sources, which are all located within 500 kpc (∼1') of the cluster center and have radio luminosities P1.4 GHz > 1.6 × 1024 W Hz-1. The typical host galaxies are among the highest stellar mass galaxies in the cluster. The exceptional radio activity among the massive galaxy population appears to be linked to the dynamical state of the cluster. The galaxy distribution suggests an ongoing merger, with a subgroup found to the northwest of the main cluster. Furthermore, two of the five sources are classified as bent-tail sources, with one being a potential wide-angle tail/hybrid morphology radio source, indicating a dynamic environment. The cluster also lies in a region of the mass-richness plane occupied by other merging clusters in the Massive and Distant Clusters of WISE Survey. The data suggest that during the merger phase, radio activity can be dramatically enhanced, which would contribute to the observed trend of increased radio activity in clusters with increasing redshift.

Keywords: galaxy evolution; galaxy clusters; high-redshift galaxy clusters; agn host galaxies; intracluster medium; active galactic nuclei; radio interferometry; radio continuum emission; radio galaxies; fanaroff-riley radio galaxies; tailed radio galaxies; radio lobes
The Stellar-mass Function of Long Gamma-Ray Burst Host Galaxies

Long gamma-ray bursts (GRBs) have been discussed as a potential tool to probe the cosmic star formation rate (SFR) for a long time. Some studies found an enhancement in the GRB rate relative to the galaxy-inferred SFR at high redshifts, which indicates that GRBs may not be good tracers of star formation. However, in these studies, the GRB rate measured at any redshift is an average over all galaxies at that epoch. A deep understanding of the connection between GRB production and environment also needs to characterize the population of GRB host galaxies directly. Based on a complete sample of GRB hosts, we constrain the stellar-mass function (SMF) of GRB hosts, and examine redshift evolution in the GRB host population. Our results confirm that a strong redshift evolution in energy (with an evolution index of $\delta ={2.47}_{-0.89}^{+0.73}$ ) or in density ( $\delta ={1.82}_{-0.59}^{+0.22}$ ) is needed in order to account for the observations. The GRB host SMF can be well described by the Schechter function with a power-law index ξ ≈ -1.10 and a break mass M b,0 ≈ 4.9 × 1010 M ⊙, independent of the assumed evolutionary effects. This is the first formulation of the GRB host SMF. The observed discrepancy between the GRB rate and the galaxy-inferred SFR may also be explained by an evolving SMF.

Keywords: gamma-ray bursts; galaxies; star formation; stellar mass functions
The Peculiar Short-duration GRB 200826A and Its Supernova

Gamma-ray bursts (GRBs) are classified into long and short events. Long GRBs (LGRBs) are associated with the end states of very massive stars, while short GRBs (SGRBs) are linked to the merger of compact objects. GRB 200826A was a peculiar event, because by definition it was an SGRB, with a rest-frame duration of ~0.5 s. However, this event was energetic and soft, which is consistent with LGRBs. The relatively low redshift (z = 0.7486) motivated a comprehensive, multiwavelength follow-up campaign to characterize its host, search for a possible associated supernova (SN), and thus understand the origin of this burst. To this aim we obtained a combination of deep near-infrared (NIR) and optical imaging together with spectroscopy. Our analysis reveals an optical and NIR bump in the light curve whose luminosity and evolution are in agreement with several SNe associated to LGRBs. Analysis of the prompt GRB shows that this event follows the E p,i-E iso relation found for LGRBs. The host galaxy is a low-mass star-forming galaxy, typical of LGRBs, but with one of the highest star formation rates, especially with respect to its mass ( $\mathrm{log}{M}_{* }/{M}_{\odot }=8.6$ , SFR ~ 4.0 M ⊙ yr-1). We conclude that GRB 200826A is a typical collapsar event in the low tail of the duration distribution of LGRBs. These findings support theoretical predictions that events produced by collapsars can be as short as 0.5 s in the host frame and further confirm that duration alone is not an efficient discriminator for the progenitor class of a GRB. * Based on data obtained with the LBT programs: LBT-2019B-18 (PI A. Rossi), DDT-2019B-9 (PI P. D'Avanzo), and LD-2020B-0100 (PI. B. Rothberg); and the TNG programme A41 TAC15 (PI V. D'Elia).

Keywords: gamma-ray bursts; core-collapse supernovae; supernovae
Stellar Bars in Isolated Gas-rich Spiral Galaxies Do Not Slow Down

Elongated bar-like features are ubiquitous in galaxies, occurring at the centers of approximately two-thirds of spiral disks in the nearby Universe. Due to gravitational interactions between the bar and the other components of galaxies, it is expected that angular momentum and matter will redistribute over long (Gyr) timescales in barred galaxies. Previous work ignoring the gas phase of galaxies has conclusively demonstrated that bars should slow their rotation over time due to their interaction with dark matter halos. We have performed a simulation of a Milky Way-like galactic disk hosting a strong bar, including a state-of-the-art model of the interstellar medium and a live dark matter halo. In this simulation, the bar pattern does not slow down over time, and instead it remains at a stable, constant rate of rotation. This behavior has been observed in previous simulations using more simplified models for the interstellar gas, but the apparent lack of secular evolution has remained unexplained. We find that the presence of the gas phase arrests the process by which the dark matter halo slows down a bar, a phenomenon we term bar locking. This locking is responsible for stabilizing the bar pattern speed. We find that, in a Milky Way-like disk, a gas fraction of only about 5% is necessary for this mechanism to operate. Our result naturally explains why nearly all observed bars rotate rapidly and is especially relevant for our understanding of how the Milky Way arrived at its present state.

Keywords: barred spiral galaxies; hydrodynamical simulations; galaxy dynamics; milky way dynamics; milky way evolution; milky way galaxy
Gas Infalling Motions in the Envelopes of Very Low Luminosity Objects

We present the results of a single-dish survey toward 95 very low luminosity objects (VeLLOs) in optically thick (HCN 1-0) and thin (N2H+ 1-0) lines performed for the purpose of understanding the physical processes of inward motions in the envelopes of the VeLLOs and characterizing their true nature. The normalized velocity differences ( $\delta {V}_{\mathrm{HCN}}$ ) between the peak velocities of the two lines were derived for 41 VeLLOs detected in both lines. The δV distribution of these VeLLOs is found to be significantly skewed to the blue, indicating the dominance of infalling motions in their envelopes. The infall speeds were derived for 15 infall candidates by using the HILL5 radiative transfer model. The speeds were in the range of 0.03-0.3 km s-1, with a median value of 0.16 km s-1, consistent with the gravitational freefall speeds from pressure-free envelopes. The mass infall rates calculated from the infall speeds are mostly of the order of 10-6 M⊙ yr-1, with a median value of (3.4 ± 1.5) × 10-6 M⊙ yr-1. These are found to be also consistent with the values predicted with the inside-out collapse model and show a fairly good correlation with the internal luminosities of the VeLLOs. This again indicates that the infall motions observed toward the VeLLOs are likely to be due to the gravitational infall motions in their envelopes. Our study suggests that most of the VeLLOs are potentially faint protostars, while two of the VeLLOs could possibly be proto-brown dwarf candidates.

Keywords: protostars; brown dwarfs; collapsing clouds
Chemical Diversity in Protoplanetary Disks and Its Impact on the Formation History of Giant Planets

Giant planets can interact with multiple and chemically diverse environments in protoplanetary disks while they form and migrate to their final orbits. The way this interaction affects the accretion of gas and solids shapes the chemical composition of the planets and of their atmospheres. Here we investigate the effects of different chemical structures of the host protoplanetary disk on the planetary composition. We consider both scenarios of molecular (inheritance from the prestellar cloud) and atomic (complete chemical reset) initial abundances in the disk. We focus on four elemental tracers of different volatility: C, O, N, and S. We explore the entire extension of possible formation regions suggested by observations by coupling the disk chemical scenarios with N-body simulations of forming and migrating giant planets. The planet formation process produces giant planets with chemical compositions significantly deviating from that of the host disk. We find that the C/N, N/O, and S/N ratios follow monotonic trends with the extent of migration. The C/O ratio shows a more complex behavior, dependent on the planet accretion history and on the chemical structure of the formation environment. The comparison between S/N* and C/N* (where * indicates normalization to the stellar value), constrains the relative contribution of gas and solids to the total metallicity. Giant planets whose metallicity is dominated by the contribution of the gas are characterized by N/O* > C/O* > C/N* and allow to constrain the disk chemical scenario. When the planetary metallicity is instead dominated by the contribution of the solids we find that C/N* > C/O* > N/O*.

Keywords: protoplanetary disks; extrasolar gaseous giant planets; abundance ratios; planetary atmospheres; planet formation; metallicity; exoplanet atmospheric composition; chemical abundances; astrochemistry
The Observed Mass Distribution of Galactic Black Hole LMXBs Is Biased against Massive Black Holes

The discovery of gravitational-wave radiation from merging black holes (BHs) also uncovered BHs with masses in the range of ≈20-160 M⊙. In contrast, the most massive Galactic stellar-mass BH currently known has a mass of ≈21 M⊙. While low-mass X-ray binaries (LMXBs) will never independently evolve into a binary BH system, and binary evolution effects can play an important role in explaining the different BH masses found through studies of X-ray binaries and gravitational-wave events, (electromagnetic) selection effects may also play a role in this discrepancy. Assuming BH LMXBs originate in the Galactic plane, we show that the spatial distributions of the current samples of confirmed and candidate BH LMXBs are both biased to sources that lie at a large distance from the plane. Specifically, most of the confirmed and candidate BH LMXBs are found at a Galactic height larger than three times the scale height for massive star formation. In addition, the confirmed BH LMXBs are found at larger distances to the Galactic center than the candidate BH LMXBs. Interstellar absorption makes candidate BH LMXBs in the plane and bulge too faint for a dynamical mass measurement using current instrumentation. Given the observed and theoretical evidence for BH natal and/or Blaauw kicks, their relation with BH mass and binary orbital period, and the relation between outburst recurrence time and BH mass, the observational selection effects imply that the current sample of confirmed BH LMXBs is biased against the most massive BHs.

Keywords: stellar mass black holes
Retention of Long-period Gas Giant Planets: Type II Migration Revisited

During their formation, emerging protoplanets tidally interact with their natal disks. Proto-gas giant planets, with Hill radii larger than the disk thickness, open gaps and quench gas flow in the vicinity of their orbits. It is usually assumed that their type II migration is coupled to the viscous evolution of the disk. Although this hypothesis provides an explanation for the origin of close-in planets, it also encounters a predicament on the retention of long-period orbits for most gas giant planets. Moreover, numerical simulations indicate that the planets' migrations are not solely determined by the viscous diffusion of their natal disk. Here we carry out a series of hydrodynamic simulations combined with analytic studies to examine the transition between different paradigms of type II migration. We find a range of planetary mass for which gas continues to flow through a severely depleted gap so that the surface density distribution in the disk region beyond the gap is maintained in a quasi-steady state. The associated gap profile modifies the location of corotation and Lindblad resonances. In the proximity of the planet's orbit, high-order Lindblad and corotation torque are weakened by the gas depletion in the gap, while low-order Lindblad torques near the gap walls preserve their magnitude. Consequently, the intrinsic surface density distribution of the disk delicately determines both the pace and direction of the planets' type II migration. We show that this effect might stall the inward migration of giant planets and preserve them in disk regions where the surface density is steep.

Keywords: planet formation; protoplanetary disks; exoplanet systems
The EXCITING Experiment Exploring the Behavior of Nitrogen and Noble Gases in Interstellar Ice Analogs

Comets represent some of the most pristine bodies in our solar system and can provide a unique insight into the chemical makeup of the early solar system. Due to their icy volatile-rich nature, they may have played an important role in delivering volatile elements and organic material to the early Earth. Understanding how comets form can therefore provide a wealth of information on how the composition of volatile elements evolved in the solar system from the presolar molecular cloud up until the formation of the terrestrial planets. Because noble gases are chemically inert and have distinct condensation temperatures, they can be used to infer the temperatures of formation and thermal history of cometary ices. In this work, we present a new experimental setup called EXCITING to investigate the origin and formation conditions of cometary ices. By trapping nitrogen and noble gases in amorphous water ice, our experiment is designed to study the elemental and isotopic behavior of volatile elements in cometary ice analogs. We report new results of noble gas and nitrogen enrichment in cometary ice analogs and discuss the limitations of the experimental conditions in light of those supposed for comets. We show that forming ice analogs at ~70 K best reproduce the noble gas and N2 abundances of comet 67P/Churyumov-Gerasimenko, considering a solar-like starting composition. This formation temperature is higher than previous estimates for cometary ices and suggests that the formation of cometary building blocks may have occurred in the protosolar nebula rather than in the colder molecular cloud.

Keywords: comet volatiles; comet origins
Sputtering Behavior of Rough, Polycrystalline Mercury Analogs

The solar wind continuously impacts on rocky bodies in space, eroding their surface, thereby contributing significantly to the exosphere formations. The BepiColombo mission to Mercury will investigate the Hermean exosphere, which makes an understanding of the precise formation processes crucial for evaluation of the acquired data. We therefore developed an experimental setup with two microbalances that allows us to compare the sputter behavior of deposited thin solid layers with that of real mineral samples in the form of pressed powder. In addition, this technique is used to study the angular distribution of the sputtered particles. Using 4 keV He+ and 2 keV Ar+ ions, the sputter behavior of pellets of the minerals enstatite (MgSiO3) and wollastonite (CaSiO3) is studied, because these minerals represent analogs for the surface of the planet Mercury or the Moon. Pellets of powdered enstatite show significantly lower sputter yields than thin amorphous enstatite films prepared by pulsed laser deposition. 3D simulations of sputtering based on surface topography data from atomic force microscopy show that the observed reduction can be explained by the much rougher pellet surface alone. We therefore conclude that sputter yields from amorphous thin films can be applied to surfaces of celestial bodies exposed to ion irradiation, provided the effects of surface roughness, as encountered in realistic materials in space, are adequately accounted for. This also implies that taking surface roughness into account is important for modeling of the interaction of the solar wind with the surface of Mercury.

Keywords: mercury (planet); solar wind; exosphere; laboratory astrophysics
Neutrino Cadence of TXS 0506+056 Consistent with Supermassive Binary Origin

On 2022 September 18, an alert by the IceCube Collaboration indicated that a ~170 TeV neutrino arrived in directional coincidence with the blazar TXS 0506+056. This event adds to two previous pieces of evidence that TXS 0506+056 is a neutrino emitter, i.e., a neutrino alert from its direction on 2017 September 22, and a 3σ signature of a dozen neutrinos in 2014/2015. De Bruijn el al. showed that two previous neutrino emission episodes from this blazar could be due to a supermassive binary black hole (SMBBH) central engine where jet precession close to the final coalescence of the binary results in periodic emission. This model predicted a new emission episode consistent with the 2022 September 18 neutrino observation by IceCube. Here, we show that the neutrino cadence of TXS 0506+056 is consistent with an SMBBH origin. We find that the emission episodes are consistent with an SMBBH with mass ratios q ≲ 0.3 for a total black hole mass of M tot ≳ 3 · 108 M ⊙. For the first time, we calculate the characteristic strain of the gravitational wave emission of the binary, and show that the merger could be detectable by LISA for black hole masses <5 · 108 M ⊙ if the mass ratios are in the range 0.1 ≲ q ≲ 0.3. We predict that there can be a neutrino flare existing in the still-to-be-analyzed IceCube data peaking some time between 2019 August and 2021 January if a precessing jet is responsible for all three detected emission episodes. The next flare is expected to peak in the period 2023 January to 2026 August. Further observation will make it possible to constrain the mass ratio as a function of the total mass of the black hole more precisely and would open the window toward the preparation of the detection of SMBBH mergers.

Keywords: neutrino astronomy; gravitational waves; active galaxies; blazars; supermassive black holes; gamma-ray sources; high-energy cosmic radiation; secondary cosmic rays
Turbulence in Zeeman Measurements from Molecular Clouds

Magnetic fields (B fields) play an important role in molecular cloud fragmentation and star formation but are very difficult to detect. The temporal correlation between the field strength (B) and gas density (n) of an isolated cloud has been suggested as an indication of the dynamical importance of B fields relative to self-gravity. This temporal B-n relation is, however, unobservable. What can be observed using Zeeman measurements are the "spatial B-n relations" from the current plane of the sky. Nevertheless, the temporal B-n relation argument has still been widely used to interpret observations. Here we present the first numerical test of the legitimacy of this interpretation. From a simulation that can reproduce the observed Zeeman spatial B ∝ n 2/3 relation, we found that temporal B -n relations of individual cores bear no resemblance to the spatial B -n relations. This result inspired us to discover that the true mechanism behind the 2/3 index is random turbulence compression instead of symmetrical gravitational contraction.

Keywords: interstellar medium; star formation