adsabs/SciX_UAT_keywords huggingface dataset:
Using Gravitational Waves to Distinguish between Neutron Stars and Black Holes in Compact Binary Mergers

In 2017 August, the first detection of a binary neutron star merger, GW170817, made it possible to study neutron stars in compact binary systems using gravitational waves. Despite being the loudest gravitational-wave event detected to date (in terms of signal-to-noise ratio), it was not possible to unequivocally determine that GW170817 was caused by the merger of two neutron stars instead of two black holes from the gravitational-wave data alone. That distinction was primarily due to the accompanying electromagnetic counterpart. This raises the question: under what circumstances can gravitational-wave data alone, in the absence of an electromagnetic signal, be used to distinguish between different types of mergers? Here, we study whether a neutron star-black hole binary merger can be distinguished from a binary black hole merger using gravitational-wave data alone. We build on earlier results using chiral effective field theory to explore whether the data from LIGO and Virgo, LIGO A+, LIGO Voyager, the Einstein Telescope, or Cosmic Explorer could lead to such a distinction. The results suggest that the present LIGO-Virgo detector network will most likely be unable to distinguish between these systems even with the planned near-term upgrades. However, given an event with favorable parameters, third-generation instruments such as Cosmic Explorer will be capable of making this distinction. This result further strengthens the science case for third-generation detectors.

Keywords: gravitational wave astronomy; gravitational waves; neutron stars; compact objects; gravitational wave detectors
Inverse Compton Emission and Cooling of Relativistic Particles Accelerated at Shear Boundary Layers in Relativistic Jets

Both observational evidence and theoretical considerations from magnetohydrodynamic simulations of jets suggest that the relativistic jets of active galactic nuclei (AGN) are radially stratified, with a fast inner spine surrounded by a slower-moving outer sheath. The resulting relativistic shear layers are a prime candidate for the site of relativistic particle acceleration in the jets of AGNs and gamma-ray bursts (GRBs). In this article, we present outcomes of particle-in-cell simulations of magnetic-field generation and particle acceleration in the relativistic shear boundary layers (SBLs) of jets in AGNs and GRBs. We investigate the effects of inverse Compton cooling on relativistic particles that are accelerated in the SBLs of relativistic jets, including the self-consistent calculation of the radiation spectrum produced by inverse Compton scattering of relativistic electrons in an isotropic external soft photon field. We find that the Compton cooling can be substantial, depending on the characteristic energy (blackbody temperature and energy density) of the external radiation field. The produced Compton emission is highly anisotropic and more strongly beamed along the jet direction than the characteristic 1/Γ pattern expected from intrinsically isotropic emission in the comoving frame of an emission region moving along the jet with a bulk Lorentz factor Γ. We suggest that this may resolve the long-standing problem of the Doppler factor crisis.

Keywords: relativistic jets; active galactic nuclei; gamma-ray bursts
A Simple Spectroscopic Technique to Identify Rejuvenating Galaxies

Rejuvenating galaxies are unusual galaxies that fully quench and then subsequently experience a "rejuvenation" event to become star-forming once more. Rejuvenation rates vary substantially in models of galaxy formation: 10%-70% of massive galaxies are expected to experience rejuvenation by z = 0. Measuring the rate of rejuvenation is therefore important for calibrating the strength of star-formation feedback mechanisms. However, these observations are challenging because rejuvenating systems blend in with normal star-forming galaxies in broadband photometry. In this paper, we use the galaxy spectral energy distribution-fitting code Prospector to search for observational markers that distinguish normal star-forming galaxies from rejuvenating galaxies. We find that rejuvenating galaxies have smaller Balmer absorption line equivalent widths (EWs) than normal star-forming galaxies. This is analogous to the well-known "K+A" or post-starburst galaxies, which have strong Balmer absorption due to A-stars dominating the light: in this case, rejuvenating systems have a lack of A-stars, instead resembling "O-A" systems. We find star-forming galaxies that have Hβ, Hγ, and/or Hδ absorption EWs ≲3 Å corresponds to a highly pure selection of rejuvenating systems. Interestingly, while this technique is highly effective at identifying mild rejuvenation, "strongly" rejuvenating systems remain nearly indistinguishable from star-forming galaxies due to the well-known stellar outshining effect. We conclude that measuring Balmer absorption line EWs in star-forming galaxy populations is an efficient method to identify rejuvenating populations, and discuss several techniques to either remove or resolve the nebular emission which typically lies on top of these absorption lines.

Keywords: galaxy evolution; galaxy formation; green valley galaxies; star formation; galaxy accretion; post-starburst galaxies
Variability and Parameter Dependence of Hard X-Ray Obscuration Around Supermassive Black Holes in Active Galaxies

We investigate hard X-ray obscuration of Active Galactic Nuclei (AGNs) by considering photoionization processes for a number of simulated accretion-disk winds in our magnetohydrodynamic (MHD) framework. To follow up our earlier work on calculating synthetic AGN obscuration functions, we are motivated in this work to expand our examination of the dependences of obscuration on individual parameters associated with MHD wind and coronal X-ray such as: X-ray luminosity L ion, photon index Γ, density of the wind n o and its radial gradient p where n ∝ n o r -p . We find that AGN appear to undergo a relatively drastic transition from more obscured state (e.g., N H ≳ 1022 cm-2) to unobscured state (i.e., N H ≲ 1022 cm-2) as p approaches to ~1.1 in these calculations. In the current formalism, luminosity is linearly coupled to wind density (i.e., L X ∝ n o ), and our calculations also indicate AGN become more obscured at higher luminosity. We further discuss the plausibility of the current model in comparison with observations.

Keywords: high energy astrophysics; magnetohydrodynamics; agn host galaxies; x-ray active galactic nuclei; radiative magnetohydrodynamics; radiative transfer simulations
Digging into the Interior of Hot Cores with ALMA: Spiral Accretion into the High-mass Protostellar Core G336.01-0.82

We observed the high-mass star-forming core G336.01-0.82 at 1.3 mm and 0.″05 (~150 au) angular resolution with the Atacama Large Millimeter/submillimeter Array (ALMA) as part of the Digging into the Interior of Hot Cores with ALMA survey. These high-resolution observations reveal two spiral streamers feeding a circumstellar disk at opposite sides in great detail. Molecular line emission from CH3OH shows velocity gradients along the streamers consistent with infall. Similarly, a flattened envelope model with rotation and infall implies a mass larger than 10 M ☉ for the central source and a centrifugal barrier of 300 au. The location of the centrifugal barrier is consistent with local peaks in the continuum emission. We argue that gas brought by the spiral streamers is accumulating at the centrifugal barrier, which can result in future accretion burst events. A total high infall rate of ~4 × 10-4 M ☉ yr-1 is derived by matching models to the observed velocity gradient along the streamers. Their contribution accounts for 20%-50% the global infall rate of the core, indicating streamers play an important role in the formation of high-mass stars.

Keywords: star formation; star forming regions; massive stars
A Channel to Form Fast-spinning Black Hole-Neutron Star Binary Mergers as Multimessenger Sources

After the successful detection of a gravitational-wave (GW) signal and its associated electromagnetic (EM) counterparts from GW170817, neutron star-black hole (NSBH) mergers have been highly expected to be the next type of multimessenger source. However, despite the detection of several NSBH merger candidates during the GW third observation run, no confirmed EM counterparts from these sources have been identified. The most plausible explanation is that these NSBH merger candidates were plunging events mainly because the primary black holes (BHs) had near-zero projected aligned spins based on GW observations. In view of the fact that neutron stars (NSs) can be easily tidally disrupted by BHs with high projected aligned spins, we study an evolution channel to form NSBH binaries with fast-spinning BHs, the properties of BH mass and spin, and their associated tidal disruption probability. We find that if the NSs are born first, the companion helium stars would be tidally spun up efficiently, and would thus finally form fast-spinning BHs. If BHs do not receive significant natal kicks at birth, these NSBH binaries that can merge within Hubble time would have BHs with projected aligned spins χ z ≳ 0.8 and, hence, can certainly allow tidal disruption to happen. Even if significant BH kicks are considered for a small fraction of NSBH binaries, the projected aligned spins of BHs are χ z ≳ 0.2. These systems can still be disrupted events unless the NSs are very massive. Thus, NS-first-born NSBH mergers would be promising multimessenger sources. We discuss various potential EM counterparts associated with these systems and their detectability in the upcoming fourth observation run.

Keywords: gravitational waves; close binary stars; black holes; neutron stars
Features of Magnetic Field Switchbacks in Relation to the Local-field Geometry of Large-amplitude Alfvénic Oscillations: Wind and PSP Observations

In this Letter, we report observations of magnetic switchback (SB) features near 1 au using data from the Wind spacecraft. These features appear to be strikingly similar to the ones observed by the Parker Solar Probe mission closer to the Sun: namely, one-sided spikes (or enhancements) in the solar-wind bulk speed V that correlate/anticorrelate with the spikes seen in the radial-field component B R . In the solar-wind streams that we analyzed, these specific SB features near 1 au are associated with large-amplitude Alfvénic oscillations that propagate outward from the Sun along a local background (prevalent) magnetic field B 0 that is nearly radial. We also show that, when B 0 is nearly perpendicular to the radial direction, the large-amplitude Alfvénic oscillations display variations in V that are two sided (i.e., V alternately increases and decreases depending on the vector Δ B = B - B 0). As a consequence, SBs may not always appear as one-sided spikes in V, especially at larger heliocentric distances where the local background field statistically departs from the radial direction. We suggest that SBs can be well described by large-amplitude Alfvénic fluctuations if the field rotation is computed with respect to a well-determined local background field that, in some cases, may deviate from the large-scale Parker field.

Keywords: heliosphere; solar wind
Solar-cycle Variations of South Atlantic Anomaly Proton Intensities Measured with the PAMELA Mission

We present a study of the solar-cycle variations of >80 MeV proton flux intensities in the lower edge of the inner radiation belt, based on the measurements of the Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics (PAMELA) mission. The analyzed data sample covers an ~8 yr interval from 2006 July to 2014 September, thus spanning from the decaying phase of the 23rd solar cycle to the maximum of the 24th cycle. We explored the intensity temporal variations as a function of drift shell and proton energy, also providing an explicit investigation of the solar modulation effects at different equatorial pitch angles. PAMELA observations offer new important constraints for the modeling of low-altitude particle radiation environment at the highest trapping energies.

Keywords: cosmic rays; van allen radiation belts
Modeling Neutron Star Matter in the Age of Multimessenger Astrophysics

The interpretation of available and forthcoming data obtained from multimessenger astrophysical observations-potentially providing unprecedented access to neutron star properties-will require the development of novel, accurate theoretical models of dense matter. Of great importance, in this context, will be the capability for devising a description of thermal effects applicable to the study of quantities other than the equation of state, such as the transport coefficients and the neutrino mean free path in the nuclear medium. A formalism based on correlated basis states and the cluster expansion technique has been previously employed to derive a well-behaved effective interaction-suitable for use in standard perturbation theory-from a state-of-the-art nuclear Hamiltonian, including phenomenological two- and three-nucleon potentials. Here, we provide a comprehensive and self-contained account of the extension of this approach to the treatment of finite-temperature effects, and report the results of numerical calculations of a number of properties of nuclear matter with arbitrary neutron excess and temperature up to 50 MeV.

Keywords: neutron stars
Dynamical Evolution of the Didymos-Dimorphos Binary Asteroid as Rubble Piles following the DART Impact

Previous efforts have modeled the Didymos system as two irregularly shaped rigid bodies, although it is likely that one or both components are in fact rubble piles. Here, we relax the rigid-body assumption to quantify how this affects the spin and orbital dynamics of the system following the DART impact. Given the known fundamental differences between our simulation codes, we find that faster rigid-body simulations produce nearly the same result as rubble-pile models in scenarios with a moderate value for the momentum enhancement factor, β (β ~ 3) and an ellipsoidal secondary. This indicates that the rigid-body approach is likely adequate for propagating the post-impact dynamics necessary to meet the DART Mission requirements. Although, if Dimorphos has a highly irregular shape or structure, or if β is unexpectedly large, then rubble-pile effects may become important. If Dimorphos's orbit and spin state are sufficiently excited, then surface particle motion is also possible. However, these simulations are limited in their resolution and range of material parameters, so they serve as a demonstration of principle, and future work is required to fully understand the likelihood and magnitude of surface motion.

Keywords: asteroid dynamics; asteroid rotation; asteroid satellites; natural satellite dynamics; orbits; near-earth objects; n-body simulations; n-body problem; celestial mechanics
Magnetic Activity of Millions of G-type Stars Based on the LAMOST DR10 Low-resolution Spectral and TESS Light-curve Surveys and the Future CSST Survey

The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) data release 10 (DR10) provides over 3 million G-type stellar spectra, which are important for the study of chromospheric activity of solar-like stars. We have used the iSpec program to perform spectral subtraction on the G-type stellar spectra obtained from LAMOST DR10 with a signal-to-noise ratio greater than 10. We have calculated the magnetic activity of G-type stars using Hα lines and analyzed the Hα variation. Among the more than 3 million spectra from more than 2.3 million stars, a total of 220,000 stars show excess chromospheric activity. There were a total of about 480,000 stars with repeated observations. About 390,000 stars were found to exhibit variations in the Hα line, and 14,000 stars showed changes in their radial velocity. By using the Gaia data, we determined the distances of these stars above the Galactic disk. We first concluded that the fraction of G-type active stars decreases with increasing distance above the Galactic disk. By using the Transiting Exoplanet Survey Satellite light curves, we obtained the effective fluctuation range of the light curve caused by the starspot and confirmed that there was a positive correlation between the starspot and chromospheric activity. We also concluded that ${R}_{{\rm{H}}\alpha }^{{\prime} }$ tends to be stable for Rossby number (Ro) < 0.13 and that ${R}_{{\rm{H}}\alpha }^{{\prime} }$ decreases as Ro increases in the region Ro ≥ 0.13.

Keywords: stellar activity
Lack of Correlations between Cold Molecular Gas and AGN Properties in Type 1 AGNs at z ≲ 0.5

We present new NOrthern Extended Millimeter Array (NOEMA) observations of the CO(2-1) emission in eight of the brightest Palomar-Green quasars at z ≲ 0.5 to investigate the role of active galactic nucleus (AGN) feedback in luminous quasars detected at low redshifts. We detect CO(2-1) emission in three objects, from which we derive CO luminosities, molecular gas masses and fractions, and gas depletion times. In combination with data available in the literature, we build a total sample of 138 local type 1 AGNs with CO(2-1) measurements. We compare the AGN properties with the host galaxy molecular gas properties, considering systems nondetected in CO emission. We find that the CO luminosity does not correlate with AGN luminosity and Eddington ratio, while the molecular gas fraction is weakly correlated with Eddington ratio. The type 1 AGNs can be roughly separated into two populations in terms of infrared-to-CO luminosity ratio, with one population presenting values typically found in normal star-forming systems, while the other having lower ratio values, comparable to those measured for starbursts. We find no evidence that AGN feedback rapidly quenches star formation in type 1 AGNs. Our results may imply an underlying the role of host galaxy gravitational instabilities or the fast inflow of cold gas in triggering AGN activity.

Keywords: agn host galaxies; quasars; submillimeter astronomy
Effects of the Planetary Field on the Accretion Process of a Planet in the Final Stage of Giant Planet Formation

Recent studies suggest that the magnetic field may play an important role in the formation of giant planets during the final stage of the formation process. In this paper, we construct a circumplanetary system around a planet that is in the final formation stage to investigate the effects of the planetary magnetic field on the accretion process of the planet at this stage. We find that at the early times of our magneto-hydrodynamic (MHD) simulation, the magnetic loops connecting the planet and the circumplanetary material inflate upward due to the build-up of the toroidal field pressure with magnetic islands forming inside the loops, which changes the flow pattern above the planet in comparison with the hydrodynamic case. We find that a low-density gap, which is produced by the strong magnetic pressure, appears along the disk's surface and expands as the system evolves. Accompanied by the accretion flow above the disk surface, the disk surface field lines can reconnect with the magnetic loops anchored on the planet. Thus, the material above the disk's surface can permeate into the loops anchored on the planet via reconnection and can be accreted to the planet through the loops. Comparing the results in the hydrodynamic and MHD simulations, we find that the mass accretion rate and the angular momentum transport rate from the infalling gas to the planet do not change apparently when the effects of the magnetic field are included, but these rates from the circumplanetary disk to the planet increase significantly by an order of magnitude.

Keywords: planet formation; protoplanetary disks; planetary-disk interactions; planetary science; magnetic fields; accretion
The Influence of Stellar Contamination on the Interpretation of Near-infrared Transmission Spectra of Sub-Neptune Worlds around M-dwarfs

The impact of unocculted stellar surface heterogeneities in the form of cool spots and hot faculae on the spectrum of a transiting planet has been a daunting problem for the characterization of exoplanet atmospheres. The wavelength-dependent nature of stellar surface heterogeneities imprinting their signatures on planetary transmission spectra are of concern particularly for systems of sub-Neptunes orbiting M-dwarfs. Here we present a systematic exploration of the impact of this spot-contamination on simulated near-infrared transmission spectra of sub-Neptune planets. From our analysis, we find that improper correction for stellar surface heterogeneities on transmission spectra can lead to significant bias when inferring planetary atmospheric properties. However, this bias is negligible for lower fractions of heterogeneities (<1%). Additionally, we find that acquiring a priori knowledge of stellar heterogeneities does not improve precision in constraining planetary parameters if the heterogeneities are appropriately marginalized within a retrieval; however, these are conditional on our confidence of stellar atmospheric models being accurate representations of the true photosphere. In sum, to acquire unbiased constraints when characterizing planetary atmospheres with the James Webb Space Telescope, we recommend performing joint retrievals of both the disk-integrated spectrum of the star and the stellar-contamination-corrected transmission spectrum.

Keywords: exoplanet atmospheres; m dwarf stars; hot neptunes; spectroscopy; radiative transfer; bayesian statistics; exoplanet atmospheric composition; stellar activity; starspots
Revealing the Impact of Critical Stellar Central Density on Galaxy Quenching through Cosmic Time

In a previous work, we investigated the structural and environmental dependence on quenching in the nearby universe. In this work, we extend our investigations to higher redshifts by combining galaxies from the Sloan Digital Sky Survey and The FourStar Galaxy Evolution surveys. In low density, we find a characteristic Σ1 kpc above which the quenching is initiated as indicated by their population-averaged color. ${{\rm{\Sigma }}}_{1\,\mathrm{kpc}}^{\mathrm{crit}}$ shows only a weak mass dependency at all redshifts, which suggests that the internal quenching process is more related to the physics that acts in the central region of galaxies. In high density, ${{\rm{\Sigma }}}_{1\,\mathrm{kpc}}^{\mathrm{crit}}$ for galaxies at z > 1 is almost indistinguishable from their low-density counterparts. At z < 1, ${{\rm{\Sigma }}}_{1\,\mathrm{kpc}}^{\mathrm{crit}}$ for low-mass galaxies becomes progressively strongly mass dependent, which is due to the increasingly stronger environmental effects at lower redshifts. ${{\rm{\Sigma }}}_{1\,\mathrm{kpc}}^{\mathrm{crit}}$ in low density shows strong redshift evolution with ∼1 dex decrement from z = 2.5–0. It is likely that at a given stellar mass, the host halo is on average more massive and gas-rich at higher redshifts; hence, a higher level of integrated energy from a more massive black hole (BH) is required to quench. As the halo evolves from the cold to hot accretion phase at lower redshifts, the gas is shock-heated and becomes more vulnerable to the feedback processes from active galactic nucleus as predicted by theory. Meanwhile, angular momentum quenching also becomes more effective at low redshifts, which complements a lower level of integrated energy from the BH to quench.

Keywords: galaxy evolution; galaxy quenching