adsabs/SciX_UAT_keywords huggingface dataset:
Toward First-principles Characterization of Cosmic-Ray Transport Coefficients from Multiscale Kinetic Simulations

A major uncertainty in understanding the transport and feedback of cosmic rays (CRs) within and beyond our Galaxy lies in the unknown CR scattering rates, which are primarily determined by wave-particle interaction at microscopic gyroresonant scales. The source of the waves for the bulk CR population is believed to be self-driven by the CR streaming instability (CRSI), resulting from the streaming of CRs downward a CR pressure gradient. While a balance between driving by the CRSI and wave damping is expected to determine wave amplitudes and hence the CR scattering rates, the problem involves significant scale separation with substantial ambiguities based on quasi-linear theory (QLT). Here we propose a novel "streaming box" framework to study the CRSI with an imposed CR pressure gradient, enabling first-principles measurement of the CR scattering rates as a function of environmental parameters. By employing the magnetohydrodynamic particle-in-cell method with ion-neutral damping, we conduct a series of simulations with different resolutions and CR pressure gradients and precisely measure the resulting CR scattering rates in steady state. The measured rates show scalings consistent with QLT, but with a normalization smaller by a factor of several than typical estimates based on the single-fluid treatment of CRs. A momentum-by-momentum treatment provides better estimates when integrated over momentum but is also subject to substantial deviations, especially at small momentum. Our framework thus opens up the path toward providing comprehensive subgrid physics for macroscopic studies of CR transport and feedback in broad astrophysical contexts.

Keywords: cosmic rays; magnetohydrodynamics; alfven waves; plasma astrophysics
Cosmic Sands. II. Challenges in Predicting and Measuring High-z Dust Temperatures

In the current era of high-z galaxy discovery with JWST and the Atacama Large Millimeter/submillimeter Array, our ability to study the stellar populations and interstellar medium conditions in a diverse range of galaxies at Cosmic Dawn has rapidly improved. At the same time, the need to understand the current limitations in modeling galaxy formation processes and physical properties in order to interpret these observations is critical. Here, we study the challenges in modeling galaxy dust temperatures, both in the context of forward modeling galaxy spectral properties from a hydrodynamical simulation and via backwards modeling galaxy physical properties from mock observations of far-infrared dust emission. Using the SIMBA model for galaxy formation combined with POWDERDAY radiative transfer, we can accurately predict the evolution of dust at high redshift, though several aspects of the model are essentially free parameters (dust composition, subresolution dust in star-forming regions) that dull the predictive power of the model dust temperature distributions. We also highlight the uncertainties in the backwards modeling methods, where we find the commonly used models and assumptions to fit far-infrared spectral energy distributions and infer dust temperatures (e.g., single temperature, optically thin modified blackbody) largely fail to capture the complexity of high-z dusty galaxies. We caution that conclusions inferred from both simulations—limited by resolution and post-processing techniques—and observations—limited by sparse data and simplistic model parameterizations—are susceptible to unique and nuanced uncertainties that can limit the usefulness of current high-z dust measurements.

Keywords: interstellar dust; spectral energy distribution; radiative transfer simulations; astronomical simulations
The HI Mass Function of Star-forming Galaxies at z 0.35

The neutral atomic hydrogen (HI) mass function (HIMF) describes the distribution of the HI content of galaxies at any epoch; its evolution provides an important probe of models of galaxy formation and evolution. Here, we report Giant Metrewave Radio Telescope HI 21 cm spectroscopy of blue star-forming galaxies at z ≈ 0.20-0.42 in the Extended Groth Strip, which has allowed us to determine the scaling relation between the average HI mass (M HI ) and the absolute B-band magnitude (M B ) of such galaxies at z ≈ 0.35, by stacking the HI 21 cm emission signals of galaxy subsamples in different M B ranges. We combine this M HI - M B scaling relation (with a scatter assumed to be equal to that in the local universe) with the known B-band luminosity function of star-forming galaxies at these redshifts to determine the HIMF at z ≈ 0.35. We show that the use of the correct scatter in the M HI - M B scaling relation is critical for an accurate estimate of the HIMF. We find that the HIMF has evolved significantly from z ≈ 0.35 to z ≈ 0, i.e., over the last 4 Gyr, especially at the high-mass end. High-mass galaxies, with M HI ≳ 1010 M ⊙, are a factor of ≈3.4 less prevalent at z ≈ 0.35 than at z ≈ 0. Conversely, there are more low-mass galaxies, with M HI ≈ 109 M ⊙, at z ≈ 0.35 than in the local universe. While our results may be affected by cosmic variance, we find that massive star-forming galaxies have acquired a significant amount of HI through merger events or accretion from the circumgalactic medium over the past 4 Gyr.

Keywords: galaxy evolution; radio spectroscopy; high-redshift galaxies; h i line emission
Compact Symmetric Objects. III. Evolution of the High-luminosity Branch and a Possible Connection with Tidal Disruption Events

We use a sample of 54 compact symmetric objects (CSOs) to confirm that there are two unrelated CSO classes: an edge-dimmed, low-luminosity class (CSO 1), and an edge-brightened, high-luminosity class (CSO 2). Using blind tests, we show that CSO 2s consist of three subclasses: CSO 2.0, having prominent hot spots at the leading edges of narrow jets and/or narrow lobes; CSO 2.2, without prominent hot spots and with broad jets and/or lobes; and CSO 2.1, which exhibit mixed properties. Most CSO 2s do not evolve into larger jetted active galactic nuclei (AGN), but spend their whole life cycle as CSOs of size ≲500 pc and age ≲5000 yr. The minimum energies needed to produce the radio luminosity and structure in CSO 2s range from ∼10‑4 M ⊙ c 2 to ∼7 M ⊙ c 2. We show that the transient nature of most CSO 2s, and their birth rate, can be explained through ignition in the tidal disruption events of stars. We also consider possibilities of tapping the spin energy of the supermassive black hole, and tapping the energy of the accretion disk. Our results demonstrate that CSOs constitute a large family of AGN in which we have thus far studied only the brightest. More comprehensive CSO studies, with higher sensitivity, resolution, and dynamic range, will revolutionize our understanding of AGN and the central engines that power them.

Keywords: active galactic nuclei; active galaxies; relativistic jets; tidal disruption
The Emerging Stellar Complex in Mon R2: Membership and Optical Variability Classification

Monoceros R2 (Mon R2) is one of the closest large active star-forming regions. This extremely young and partially embedded region provides an excellent laboratory for studying star formation and the early evolution of young stellar objects (YSOs). In this paper, we conduct an optical study of the greater Mon R2 region. Beginning with 1690 previously identified candidate YSOs, we used 496 sources with good proper motions and parallaxes from Gaia Data Release (DR) 3 to determine the astrometric properties for likely members of Mon R2. We then used both astrometric and photometric (isochronal and variability) criteria to determine that 308 of these stars are highly probable members. Using the same criteria, we considered a broad area search around Mon R2 in Gaia DR3 and separated candidate members from field stars. In total, we selected 651 likely new cluster members that had been missed in the previous X-ray and infrared excess selection techniques used in the past to establish cluster membership. Revised astrometric properties of the cluster were found using the combined sample of ∼959 highly probable member stars. For the literature plus the new candidate member list, optical light curves were compiled from the Zwicky Transient Facility. For 470 identified variable sources, we attempted classification based on the flux asymmetry (M) and quasiperiodicity (Q) metrics. We find that Mon R2 is dominated by quasiperiodic symmetric variables, with aperiodic sources also a significant population. A few tens of large-amplitude variables are identified that may be of interest for further study.

Keywords: pre-main sequence stars; stellar associations; star forming regions; t tauri stars; variable stars; young stellar objects
CTCV J2056-3014: An X-Ray-faint Intermediate Polar Harboring an Extremely Fast-spinning White Dwarf

We report on XMM-Newton X-ray observations that reveal CTCV J2056-3014 to be an unusual accretion-powered, intermediate polar (IP) system. It is a member of the class of X-ray-faint IPs whose space density remains unconstrained but potentially very high, with Lx,0.3-12 keV of 1.8 × 1031 erg s-1. We discovered a coherent 29.6 s pulsation in X-rays that was also revealed in our reanalysis of published optical data, showing that the system harbors the fastest-spinning, securely known white dwarf (WD) so far. There is no substantial X-ray absorption in the system. Accretion occurs at a modest rate (∼6 × 10-12 M⊙ yr-1) in a tall shock above the WD, while the star seems to be spinning in equilibrium and to have low magnetic fields. Further studies of CTCV J2056-3014 potentially have broad implications on the origin of magnetic fields in WDs, on the population and evolution of magnetic cataclysmic variables, and also on the physics of matter around rapidly rotating magnetic WDs.

Keywords: cataclysmic variable stars; x-ray binary stars; dq herculis stars
The PHANGS-AstroSat Atlas of Nearby Star-forming Galaxies

We present the Physics at High Angular resolution in Nearby GalaxieS (PHANGS)-AstroSat atlas, which contains UV imaging of 31 nearby star-forming galaxies captured by the Ultraviolet Imaging Telescope on the AstroSat satellite. The atlas provides a homogeneous data set of far-UV and near-UV maps of galaxies within a distance of 22 Mpc and a median angular resolution of 1.″4 (corresponding to a physical scale between 25 and 160 pc). After subtracting a uniform UV background and accounting for Milky Way extinction, we compare our estimated flux densities to GALEX observations, finding good agreement. We find candidate extended UV disks around the galaxies NGC 6744 and IC 5332. We present the first statistical measurements of the clumping of the UV emission and compare it to the clumping of molecular gas traced with the Atacama Large Millimeter/submillimeter Array (ALMA). We find that bars and spiral arms exhibit the highest degree of clumping, and the molecular gas is even more clumped than the far-UV (FUV) emission in galaxies. We investigate the variation of the ratio of observed FUV to Hα in different galactic environments and kiloparsec-sized apertures. We report that ∼65% of the variation of the log10(FUV/Hα) can be described through a combination of dust attenuation with star formation history parameters. The PHANGS-AstroSat atlas enhances the multiwavelength coverage of our sample, offering a detailed perspective on star formation. When integrated with PHANGS data sets from ALMA, the Very Large Telescope-MUSE, the Hubble Space Telescope, and JWST, it develops our comprehensive understanding of attenuation curves and dust attenuation in star-forming galaxies.

Keywords: molecular gas; interstellar medium; ultraviolet astronomy; stellar astronomy
Growth and Morphology of Water-, Methanol-, and Ethanol-ice Dust Grains Formed in an Astrophysically Relevant Plasma Experiment

Ice dust grains composed of water, methanol, and ethanol are successfully produced in a laboratory plasma experiment operating at astrophysically relevant temperatures. Both methanol- and ethanol-ice grains grow in an elongated and branched way similar to water-ice grains formed in a plasma. The experiment reveals that methanol- and ethanol-ice grains grow faster, larger, and more branched (spikier) than water-ice grains. The observed growth features seem to be related to the fact that more source molecules and monomer grains can exist in the system at the same temperature. The observed morphology is in agreement with the characteristics of the diffusion-limited aggregation. We also find that larger and more branched ice grains form when the ambient gas pressure is low or the mass of the ambient gas is light, indicating that the aggregation of small grains is enhanced under these conditions.

Keywords: laboratory astrophysics; plasma astrophysics; circumstellar dust; interstellar dust; planetary rings
The X-Ray and Radio Loud Fast Blue Optical Transient AT2020mrf: Implications for an Emerging Class of Engine-driven Massive Star Explosions

We present AT2020mrf (SRGe J154754.2+443907), an extra-galactic (z = 0.1353) fast blue optical transient (FBOT) with a rise time of t g,rise = 3.7 days and a peak luminosity of M g,peak = -20.0. Its optical spectrum around peak shows a broad (v ~ 0.1c) emission feature on a blue continuum (T ~ 2 × 104 K), which bears a striking resemblance to AT2018cow. Its bright radio emission (ν L ν = 1.2 × 1039 erg s-1; ν rest = 7.4 GHz; 261 days) is similar to four other AT2018cow-like events, and can be explained by synchrotron radiation from the interaction between a sub-relativistic (≳0.07-0.08c) forward shock and a dense environment ( $\dot{M}\lesssim {10}^{-3}\,{M}_{\odot }\,{\mathrm{yr}}^{-1}$ for v w = 103 km s-1). AT2020mrf occurs in a galaxy with M * ~ 108 M ⊙ and specific star formation rate ~10-10 yr-1, supporting the idea that AT2018cow-like events are preferentially hosted by dwarf galaxies. The X-ray luminosity of AT2020mrf is the highest among FBOTs. At 35-37 days, SRG/eROSITA detected luminous (L X ~ 2 × 1043 erg s-1; 0.3-10 keV) X-ray emission. The X-ray spectral shape (f ν ∝ ν -0.8) and erratic intraday variability are reminiscent of AT2018cow, but the luminosity is a factor of ~20 greater than AT2018cow. At 328 days, Chandra detected it at L X ~ 1042 erg s-1, which is >200 times more luminous than AT2018cow and CSS161010. At the same time, the X-ray emission remains variable on the timescale of ~1 day. We show that a central engine, probably a millisecond magnetar or an accreting black hole, is required to power the explosion. We predict the rates at which events like AT2018cow and AT2020mrf will be detected by SRG and Einstein Probe.

Keywords: x-ray transient sources; radio transient sources; supernovae; core-collapse supernovae; high energy astrophysics; sky surveys
Flare-like Variability of the Mg II λ2798 Å Emission Line and UV Fe II Band in the Blazar CTA 102

We report on the detection of a statistically significant flare-like event in the Mg II λ 2798 Å emission line and the UV Fe II band of CTA 102 during the outburst of fall 2017. The ratio between the maximum and minimum of λ3000 Å continuum flux for the observation period (2010-2017) is 179 ± 15. Respectively, the max/min ratios 8.1 ± 10.5 and 34.0 ± 45.5 confirmed the variability of the Mg II emission line and of the Fe II band. The highest levels of emission line fluxes recorded coincide with a superluminal jet component traversing through a stationary component located ∼0.1 mas from the 43 GHz core. Additionally, comparing the Mg II line profile in the minimum of activity against the one in the maximum, we found that the latter is broader and blueshifted. As a result of these findings, we can conclude that the non-thermal continuum emission produced by material in the jet moving at relativistic speeds is related to the broad emission line fluctuations. Consequently, these fluctuations are also linked to the presence of broad-line region (BLR) clouds located ∼25 pc from the central engine, outside the inner parsec, where the canonical BLR is located. Our results suggest that during strong activity in CTA 102, the source of non-thermal emission and broad-line clouds outside the inner parsec introduces uncertainties in the estimates of black hole (BH) mass. Therefore, it is important to estimate the BH mass, using single-epoch or reverberation mapping techniques, only with spectra where the continuum luminosity is dominated by the accretion disk.

Keywords: active galaxies; blazars; emission line galaxies; relativistic jets; gamma-ray astronomy
Searching for Local Counterparts of High-redshift Poststarburst Galaxies in Integral Field Unit Spectroscopic Surveys of Nearby Galaxies

Searching in the MaNGA IFU survey, I identify nine galaxies that have strong Balmer absorption lines and weak nebular emission lines measured from the spectra integrated over the entire IFU. The spectral features measured from the bulk of the stellar light make these galaxies local analogs of high-redshift spectroscopically selected poststarburst galaxies and thus proxies to understand the mechanisms producing poststarburst galaxies at high redshifts. I present the distributions of absorption line indices and emission line strengths, as well as the stellar kinematics of these local poststarburst galaxies. Almost all local poststarburst galaxies have central compact emission line regions at the central <1 kpc, mostly powered by weak star formation activities. The age-sensitive absorption line indices EW(Hδ) and Dn4000 indicate that the stellar populations at the outskirts are older. Toy stellar population synthesis models suggest that the galaxies as a whole are experiencing a rapid decline of star formation with residual star formation activities at the centers. These features indicate that most poststarburst galaxies are the aftermath of highly dissipative processes that drive gas into centers, invoke centrally concentrated star formation, and then quench the galaxies. Meanwhile, when measurable, poststarburst galaxies have the directions of maximum stellar velocity gradients aligned with photometric major axes, which suggest against major mergers being the principal driving mechanism, while gas-rich minor mergers are plausible. While directly obtaining the same quality of spatially resolved spectra of high-redshift poststarburst galaxies is very difficult, finding proper local counterparts provides an alternative to understand quenching processes in the distant universe.

Keywords: post-starburst galaxies; galaxy quenching; galaxy ages; galaxy stellar content; optical astronomy
Polarization Signature of Companion-fed Supernovae Arising from BH-NS/BH Progenitor Systems

The formation of black hole-neutron star (BH-NS) or BH-BH systems may be accompanied by special supernova (SN) signals, due to the accretion feedback from the companion BH. The additional heating, which is mainly attributed to the Blandford-Payne mechanism, would disrupt the isotropic nature of the luminosity distribution on the surface of the SN ejecta, leading to the appearance of polarization. Here we develop a three-dimensional Monte Carlo polarization simulation code to conduct simulations for these special SNe. We find that the maximum polarization level of ~2% occurs at the peak time of SN emission in the "close-binary" scenario, while in the "faraway-binary" case maximum polarization (i.e., ~0.7%) is observed at a considerably later time than the peak of the SN. The magnitude of polarization is dependent on the degree of unevenness in the luminosity distribution and the angle between the line of sight and the equatorial direction. When considering the geometric distortion of SN ejecta at the same time, the magnitude of polarization may either increase (for a oblate ellipsoidal shape) or decrease (for a prolate ellipsoidal shape). The polarization signatures represent a promising auxiliary instrument to facilitate the identification of the companion-fed SNe. Moreover, comparing the event rate of these special SNe with the event rate density of LIGO-Virgo-detected BH-NS/BH systems could further help to distinguish the BH-NS/BH formation channel.

Keywords: supernovae; gravitational waves; black holes; polarimetry
On the Contribution of the X-Ray Source to the Extended Nebular He II Emission in IZW18

Nebular He II emission implies the presence of energetic photons (E ≥ 54 eV). Despite the great deal of effort dedicated to understanding He II ionization, its origin has remained mysterious, particularly in metal-deficient star-forming (SF) galaxies. Unfolding He II-emitting, metal-poor starbursts at z ∼ 0 can yield insight into the powerful ionization processes occurring in the primordial universe. Here we present a new study on the effects that X-ray sources have on the He II ionization in the extremely metal-poor galaxy IZw18 (Z ∼ 3% Z⊙), whose X-ray emission is dominated by a single high-mass X-ray binary (HMXB). This study uses optical integral field spectroscopy, archival Hubble Space Telescope observations, and all of the X-ray data sets publicly available for IZw18. We investigate the time-variability of the IZw18 HMXB for the first time; its emission shows small variations on timescales from days to decades. The best-fit models for the HMXB X-ray spectra cannot reproduce the observed He II ionization budget of IZw18, nor can recent photoionization models that combine the spectra of both very low metallicity massive stars and the emission from HMXB. We also find that the IZw18 HMXB and the He II-emission peak are spatially displaced at a projected distance of ≃200 pc. These results reduce the relevance of X-ray photons as the dominant He II ionizing mode in IZw18, which leaves uncertain what process is responsible for the bulk of its He II ionization. This is in line with recent work discarding X-ray binaries as the main source responsible for He II ionization in SF galaxies.

Keywords: dwarf galaxies; emission line galaxies; blue compact dwarf galaxies; high mass x-ray binary stars
Mass Loss by Atmospheric Escape from Extremely Close-in Planets

We explore atmospheric escape from close-in exoplanets with the highest mass-loss rates. First, we locate the transition from stellar X-ray and UV-driven escape to rapid Roche lobe overflow, which occurs once the 10-100 nbar pressure level in the atmosphere reaches the Roche lobe. Planets enter this regime when the ratio of the substellar radius to the polar radius along the visible surface pressure level, which aligns with a surface of constant Roche potential, is X/Z ≳ 1.2 for Jovian planets (Mp ≳ 100 M ⊕) and X/Z ≳ 1.02 for sub-Jovian planets (M p ≈ 10-100 M ⊕). Around a Sun-like star, this regime applies to orbital periods of less than two days for planets with radii of about 3-14R⊕. Our results agree with the properties of known transiting planets and can explain parts of the sub-Jovian desert in the population of known exoplanets. Second, we present detailed numerical simulations of atmospheric escape from a planet like Uranus or Neptune orbiting close to a Sun-like star that support the results above and point to interesting qualitative differences between hot Jupiters and sub-Jovian planets. We find that hot Neptunes with solar-metallicity hydrogen and helium envelopes have relatively more extended upper atmospheres than typical hot Jupiters, with a lower ionization fraction and higher abundances of escaping molecules. This is consistent with existing ultraviolet transit observations of warm Neptunes, and it might provide a way to use future observations and models to distinguish solar-metallicity atmospheres from higher-metallicity atmospheres.

Keywords: exoplanet atmospheres; hot jupiters; hot neptunes