adsabs/SciX_UAT_keywords huggingface dataset:
Turbulent Model of Crab Nebula Radiation

We construct a turbulent model of the Crab Nebula's nonthermal emission. The present model resolves a number of long-standing problems of the Kennel-Coroniti model: (I) the sigma problem, (II) the hard spectrum of radio electrons, (III) the high peak energy of gamma-ray flares, (IV) and the spatial evolution of the infrared (IR) emission. The Nebula contains two populations of injected particles: Component-I, accelerated at the wind termination shock via the Fermi-I mechanism; and Component-II, accelerated in reconnecting turbulence in highly magnetized (σ ≫ 1) plasma in the central part of the Crab Nebula. The reconnecting turbulence in Component-II extends from radio to gamma-rays: it accelerates radio electrons with a hard spectrum, destroys the large-scale magnetic flux (and thus resolves the sigma problem), and occasionally produces gamma-ray flares (from the largest-scale reconnection events). The model reproduces the broadband spectrum of the Crab Nebula, from low-frequency synchrotron emission in radio to inverse-Compton emission at TeV energies, as well as the spatially resolved evolution of the spectral indices in the IR and optical bands.

Keywords: rotation powered pulsars; stellar wind bubbles; interstellar synchrotron emission
A Joint Fermi-GBM and LIGO/Virgo Analysis of Compact Binary Mergers from the First and Second Gravitational-wave Observing Runs

We present results from offline searches of Fermi Gamma-ray Burst Monitor (GBM) data for gamma-ray transients coincident with the compact binary coalescences observed by the gravitational-wave (GW) detectors Advanced LIGO and Advanced Virgo during their first and second observing runs. In particular, we perform follow-up for both confirmed events and low significance candidates reported in the LIGO/Virgo catalog GWTC-1. We search for temporal coincidences between these GW signals and GBM-triggered gamma-ray bursts (GRBs). We also use the GBM Untargeted and Targeted subthreshold searches to find coincident gamma-rays below the onboard triggering threshold. This work implements a refined statistical approach by incorporating GW astrophysical source probabilities and GBM visibilities of LIGO/Virgo sky localizations to search for cumulative signatures of coincident subthreshold gamma-rays. All search methods recover the short gamma-ray burst GRB 170817A occurring ∼1.7 s after the binary neutron-star merger GW170817. We also present results from a new search seeking GBM counterparts to LIGO single-interferometer triggers. This search finds a candidate joint event, but given the nature of the GBM signal and localization, as well as the high joint false alarm rate of 1.1 × 10-6 Hz, we do not consider it an astrophysical association. We find no additional coincidences.

Keywords: gamma-ray bursts; gravitational waves
Gemini Planet Imager Spectroscopy of the Dusty Substellar Companion HD 206893 B

We present new near-infrared Gemini Planet Imager (GPI) spectroscopy of HD 206893 B, a substellar companion orbiting within the debris disk of its F5V star. The J, H, K1, and K2 spectra from GPI demonstrate the extraordinarily red colors of the object, confirming it as the reddest substellar object observed to date. The significant flux increase throughout the infrared presents a challenging atmosphere to model with existing grids. Best-fit values vary from 1200 to 1800 K for effective temperature and from 3.0 to 5.0 for log(g), depending on which individual wavelength band is fit and which model suite is applied. The extreme redness of the companion can be partially reconciled by invoking a high-altitude layer of submicron dust particles, similar to dereddening approaches applied to the peculiar red field L dwarf population. However, reconciling the HD 206893 B spectra with even those of the reddest low-gravity L dwarf spectra still requires the contribution of additional atmospheric dust, potentially due to the debris disk environment in which the companion resides. Orbit fitting from 4 yr of astrometric monitoring is consistent with a ∼30 yr period, an orbital inclination of 147°, and a semimajor axis of 10 au, well within the estimated disk inner radius of ∼50 au. As one of a very few substellar companions imaged interior to a circumstellar disk, the properties of this system offer important dynamical constraints on companion-disk interaction and provide a benchmark for substellar and planetary atmospheric study.

Keywords: substellar companion stars; brown dwarfs; debris disks; exoplanet atmospheric composition; orbit determination
High-resolution M-band Spectroscopy of CO toward the Massive Young Stellar Binary W3 IRS 5

We present in this paper the results of high spectral resolution (R = 88,100) spectroscopy at 4.7 μm with iSHELL/IRTF of hot molecular gas close to the massive binary protostar W3 IRS 5. The binary was spatially resolved, and the spectra of the two sources (MIR1 and MIR2) were obtained simultaneously for the first time. Hundreds of 12CO ν = 0-1, ν = 1-2 lines, and ν = 0-1 transitions of the isotopes of 12CO were detected in absorption and are blueshifted compared to the cloud velocity v LSR = -38 km s-1. We decompose and identify kinematic components from the velocity profiles and apply rotation diagram and curve-of-growth analyses to determine their physical properties. The temperatures and column densities of the identified components range from 30 to 700 K and 1021 to 1022 cm-2, respectively. Our curve-of-growth analyses consider two scenarios. One assumes a foreground slab with a partial covering factor, which well reproduces the absorption of most of the components. The other assumes a circumstellar disk with an outward-decreasing temperature in the vertical direction and reproduces the absorption of all of the hot components. We attribute the physical origins of the identified components to the foreground envelope (<100 K), post-J-shock regions (200-300 K), and clumpy structures on the circumstellar disks (~600 K). We propose that the components with a J-shock origin are akin to water maser spots in the same region and complement the physical information of water masers along the direction of their movements.

Keywords: star formation; infrared sources; interstellar molecules
Anisotropy of Long-period Comets Explained by Their Formation Process

Long-period comets coming from the Oort cloud are thought to be planetesimals formed in the planetary region on the ecliptic plane. We have investigated the orbital evolution of these bodies due to the Galactic tide. We extended our previous work and derived analytical solutions to the Galactic longitude and latitude of the direction of aphelion, L and B. Using the analytical solutions, we show that the ratio of the periods of evolution of L and B is very close to either 2 or $\infty $ for initial eccentricities ei ≃ 1, as is true for the Oort cloud comets. From the relation between L and B, we predict that Oort cloud comets returning to the planetary region are concentrated on the ecliptic plane and a second plane, which we call the "empty ecliptic." This consists in a rotation of the ecliptic around the Galactic pole by 180°. Our numerical integrations confirm that the radial component of the Galactic tide, which is neglected in the derivation of the analytical solutions, is not strong enough to break the relation between L and B derived analytically. Brief examination of observational data shows that there are concentrations near both the ecliptic and the empty ecliptic. We also show that the anomalies of the distribution of B of long-period comets mentioned by several authors are explained by the concentrations on the two planes more consistently than by previous explanations.

Keywords: long period comets; comets; oort cloud
The Relation between Morphological Asymmetry and Nuclear Activity in Low-redshift Galaxies

The morphology of galaxies reflects their assembly history and ongoing dynamical perturbations from the environment. Analyzing stacked i-band images from the Pan-STARRS1 3π Steradian Survey, we study the optical morphological asymmetry of the host galaxies of a large, well-defined sample of nearby active galactic nuclei (AGNs) to investigate the role of mergers and interactions in triggering nuclear activity. The AGNs, comprising 245 type 1 and 4514 type 2 objects, are compared with 4537 star-forming galaxies (SFGs) matched in redshift (0.04 < z < 0.15) and stellar mass (M * > 1010 M ⊙). We develop a comprehensive masking strategy to isolate the emission of the target from foreground stars and other contaminating nearby sources, all the while retaining projected companions of comparable brightness that may be major mergers. Among three variants of nonparametric indices, both the popular CAS asymmetry parameter (A CAS) and the outer asymmetry parameter (A outer) yield robust measures of morphological distortion for SFGs and type 2 AGNs, while only A outer is effective for type 1 AGNs. The shape asymmetry (A shape), by comparison, is affected more adversely by background noise. Asymmetry indices ≳0.4 effectively trace systems that are candidate ongoing mergers. Contrary to theoretical expectations, galaxy interactions and mergers are not the main drivers of nuclear activity, at least not in our sample of low-redshift, relatively low luminosity AGNs, whose host galaxies are actually significantly less asymmetric than the control sample of SFGs. Moreover, type 2 AGNs are morphologically indistinguishable from their type 1 counterparts. The level of AGN activity does not correlate with asymmetry, not even among the major merger candidates. As a by-product, we find, consistent with previous studies, that the average asymmetry of SFGs increases above the main sequence, although not all major mergers exhibit enhanced star formation.

Keywords: galaxy evolution; galaxy interactions; galaxy mergers; agn host galaxies
Electron Acceleration at Rippled Low-mach-number Shocks in High-beta Collisionless Cosmic Plasmas

Using large-scale fully kinetic two-dimensional particle-in-cell simulations, we investigate the effects of shock rippling on electron acceleration at low-Mach-number shocks propagating in high-β plasmas, in application to merger shocks in galaxy clusters. We find that the electron-acceleration rate increases considerably when the rippling modes appear. The main acceleration mechanism is stochastic shock-drift acceleration, in which electrons are confined at the shock by pitch-angle scattering off turbulence and gain energy from the motional electric field. The presence of multiscale magnetic turbulence at the shock transition and the region immediately behind the main shock overshoot is essential for electron energization. Wide-energy non-thermal electron distributions are formed both upstream and downstream of the shock. The maximum energy of the electrons is sufficient for their injection into diffusive shock acceleration. We show for the first time that the downstream electron spectrum has a power-law form with index p ≈ 2.5, in agreement with observations.

Keywords: galaxy clusters; plasma astrophysics; shocks; computational methods
On the Significance of the Thick Disks of Disk Galaxies

Thick disks are a prevalent feature observed in numerous disk galaxies, including our own Milky Way. Their significance has been reported to vary widely, ranging from a few percent to 100% of the disk mass, depending on the galaxy and the measurement method. We use the NewHorizon simulation, which has high spatial and stellar mass resolutions, to investigate the issue of the thick-disk mass fraction. We also use the NewHorizon2 simulation, which was run on the same initial conditions, but additionally traced nine chemical elements. Based on a sample of 27 massive disk galaxies with M * > 1010 M ⊙ in NewHorizon, the contribution of the thick disk was found to be 20% ± 11% in r-band luminosity or 35% ± 15% in mass to the overall galactic disk, which seems in agreement with observational data. The vertical profiles of 0, 22, and 5 galaxies are best fitted by 1, 2, or 3 ${{\rm{sech}} }^{2}$ components, respectively. The NewHorizon2 data show that the selection of thick-disk stars based on a single [α/Fe] cut is contaminated by stars of different kinematic properties, while missing the bulk of kinematically thick disk stars. Vertical luminosity profile fits recover the key properties of thick disks reasonably well. The majority of stars are born near the galactic midplane with high circularity and get heated with time via fluctuations in the force field. Depending on the star formation and merger histories, galaxies may naturally develop thick disks with significantly different properties.

Keywords: galaxy disks; galaxy stellar disks; galaxy structure; galaxy chemical evolution; hydrodynamical simulations
Formation of Multiple Populations of M5 (NGC 5904)

With our new Ca-CN-CH-NH photometry, we revisit the globular cluster (GC) M5. We find that M5 is a mono-metallic GC with a small metallicity dispersion. Our carbon abundances show that the σ[C/Fe] of the M5 CN-s population, with depleted carbon and enhanced nitrogen abundances, is significantly large for a single stellar population. Our new analysis reveals that the M5 CN-s population is well described by the two stellar populations: the CN-sI, being the major CN-s component, with the intermediate carbon and nitrogen abundance and the CN-sE with the most carbon-poor and nitrogen-rich abundance. We find that the CN-sE is significantly more centrally concentrated than the others, while CN-w and CN-sI have similar cumulative radial distributions. The red giant branch bump V magnitude, the helium abundance barometer in mono-metallic populations, of individual populations appears to be correlated with their mean carbon abundance, indicating that carbon abundances are anticorrelated with helium abundances. We propose that the CN-sE formed out of gas that experienced proton-capture processes at high temperatures in the innermost region of the proto-GC of M5 that resided in a dense ambient density environment. Shortly after, the CN-sI formed out of gas diluted from the pristine gas in the more spatially extended region, consistent with the current development of numerical simulations by others.

Keywords: stellar populations; population ii stars; hertzsprung russell diagram; globular star clusters; stellar evolution; red giant branch
The Detailed Light-curve Evolution of V1674 Her (Nova Her 2021)

We report high-cadence photometry of the ultra-fast (t2 ~ 1.2 days) nova V1674 Her during its rise to maximum light (V ~ 6.3) and the beginning of its subsequent decline. These observations from Evryscope and the Mount Laguna Observatory All-Sky Camera reveal a plateau in the pre-maximum light curve at g ~ 14 (~8 mag below peak) that lasted for at least three hours. Similar features (so-called pre-maximum halts) have been observed in some novae near maximum light, but to our knowledge the detection of a plateau in the light curve ~8 mag below peak is unprecedented.

Keywords: classical novae; light curves; time domain astronomy
Uniform Recalibration of Common Spectrophotometry Standard Stars onto the CALSPEC System Using the SuperNova Integral Field Spectrograph

We calibrate spectrophotometric optical spectra of 32 stars commonly used as standard stars, referenced to 14 stars already on the Hubble Space Telescope-based CALSPEC flux system. Observations of CALSPEC and non-CALSPEC stars were obtained with the SuperNova Integral Field Spectrograph over the wavelength range 3300-9400 Å as calibration for the Nearby Supernova Factory cosmology experiment. In total, this analysis used 4289 standard-star spectra taken on photometric nights. As a modern cosmology analysis, all presubmission methodological decisions were made with the flux scale and external comparison results blinded. The large number of spectra per star allows us to treat the wavelength-by-wavelength calibration for all nights simultaneously with a Bayesian hierarchical model, thereby enabling a consistent treatment of the Type Ia supernova cosmology analysis and the calibration on which it critically relies. We determine the typical per-observation repeatability (median 14 mmag for exposures ≳5 s), the Maunakea atmospheric transmission distribution (median dispersion of 7 mmag with uncertainty 1 mmag), and the scatter internal to our CALSPEC reference stars (median of 8 mmag). We also check our standards against literature filter photometry, finding generally good agreement over the full 12 mag range. Overall, the mean of our system is calibrated to the mean of CALSPEC at the level of ~3 mmag. With our large number of observations, careful cross-checks, and 14 reference stars, our results are the best calibration yet achieved with an integral-field spectrograph, and among the best calibrated surveys.

Keywords: flux calibration; spectrophotometry; spectrophotometric standards
Evidence for a Massive Andromeda Galaxy Using Satellite Galaxy Proper Motions

We present new mass estimates for Andromeda (M31) using the orbital angular momenta of four satellite galaxies (M33, NGC 185, NGC 147, and IC 10) derived from existing proper motions, distances, and line-of-sight velocities. We infer two masses for M31: ${M}_{\mathrm{vir}}={2.85}_{-0.77}^{+1.47}\times {10}^{12}\,{M}_{\odot }$ using satellite galaxy phase-space information derived with Hubble Space Telescope (HST)-based M31 proper motions and ${M}_{\mathrm{vir}}\,={3.02}_{-0.69}^{+1.30}\times {10}^{12}\,{M}_{\odot }$ using phase-space information derived with the weighted average of HST+Gaia-based M31 proper motions. The precision of our new M31 mass estimates (23%-50%) improves by a factor of two compared to previous mass estimates using a similar methodology with just one satellite galaxy, and places our results among the highest-precision M31 estimates in recent literature. Furthermore, our results are consistent with recently revised estimates for the total mass of the Local Group (LG), with the stellar mass-halo mass relation, and with observed kinematic data for both M31 and its entire population of satellites. An M31 mass >2.5 × 1012 M ⊙ could have major implications for our understanding of LG dynamics, M31's merger and accretion history, and our understanding of LG galaxies in a cosmological context.

Keywords: dwarf galaxies; andromeda galaxy; astrometry; astrostatistics
Reality or Mirage? Observational Test and Implications for the Claimed Extremely Magnified Quasar at z = 6.3

In the last two decades, approximately 200 quasars have been discovered at $z\gt 6$ , hosting active supermassive black holes with masses ${M}_{\bullet }\gtrsim {10}^{9}\,{M}_{\odot }$ . While these sources reflect only the tip of the iceberg of the black hole mass distribution, their detection challenges standard growth models. The most massive $z\gt 6$ black hole that was inferred thus far (J0100+2802, ${M}_{\bullet }\approx 1.2\times {10}^{10}\,{M}_{\odot }$ ) was recently claimed to be lensed, with a magnification factor $\mu =450$ . Here, we perform a consistency check of this claim, finding that the detection of such a source requires a bright-end slope $\beta \geqslant 3.7$ for the intrinsic quasar luminosity function (LF), ${\rm{\Phi }}(L)\propto {L}^{-\beta }$ . Commonly used values of $\beta \sim 2.8$ are rejected at $\gt 3\sigma $ . If the claim is confirmed, it is very unlikely that all the remaining 51 sources in the Sloan Digital Sky Survey sample are not magnified. Furthermore, it suffices that $\gtrsim 25 \% $ of the remaining sources are lensed for the intrinsic LF to differ significantly (I.e., $\gt 3\sigma $ ) from the observed one. The presence of additional extremely magnified sources in the sample would lower the requirement to $\sim 4 \% $ . Our results urge the community to perform more extended multiwavelength searches targeting $z\gt 6$ lensed quasars, also among known samples. This effort could vitally contribute to solving the open problem of the growth of the brightest $z\sim 7$ quasars.

Keywords: active galaxies; supermassive black holes; early universe; reionization; quasars; strong gravitational lensing; luminosity function
From Naked Spheroids to Disky Galaxies: How Do Massive Disk Galaxies Shape Their Morphology?

We investigate the assembly history of massive disk galaxies and describe how they shape their morphology through cosmic time. Using SHARDS and HST data, we modeled the surface brightness distribution of 91 massive galaxies at redshift 0.14 < z ≤ 1 in the wavelength range 0.5-1.6 μm, deriving the uncontaminated spectral energy distributions of their bulges and disks separately. This spectrophotometric decomposition allows us to compare the stellar population properties of each component in individual galaxies. We find that the majority of massive galaxies (~85%) build inside-out, growing their extended stellar disk around the central spheroid. Some bulges and disks could start forming at similar epochs, but these bulges grow more rapidly than their disks, assembling 80% of their mass in ~0.7 and ~3.5 Gyr, respectively. Moreover, we infer that both older bulges and older disks are more massive and compact than younger stellar structures. In particular, we find that bulges display a bimodal distribution of mass-weighted ages; i.e., they form in two waves. In contrast, our analysis of the disk components indicates that they form at z ~ 1 for both first- and second-wave bulges. This translates to first-wave bulges taking longer to acquire a stellar disk (5.2 Gyr) compared to second-wave, less compact spheroids (0.7 Gyr). We do not find distinct properties (e.g., mass, star formation timescale, and mass surface density) for the disks in both types of galaxies. We conclude that the bulge mass and compactness mainly regulate the timing of the stellar disk growth, driving the morphological evolution of massive disk galaxies.

Keywords: disk galaxies; galaxy classification systems; late-type galaxies; galaxy evolution; galaxy photometry; galaxy spectroscopy; spectral energy distribution; galaxy formation; spectrophotometry; galaxy bulges; galaxy ages; galaxy properties
Classification of Blazar Candidates of Unknown Type in Fermi 4LAC by Unanimous Voting from Multiple Machine-learning Algorithms

The Fermi fourth catalog of active galactic nuclei (AGNs) data release 3 (4LAC-DR3) contains 3407 AGNs, out of which 755 are flat spectrum radio quasars (FSRQs), 1379 are BL Lacertae objects (BL Lac objects), 1208 are blazars of unknown (BCUs) type, while 65 are non-AGNs. Accurate categorization of many unassociated blazars still remains a challenge due to the lack of sufficient optical spectral information. The aim of this work is to use high-precision, optimized machine-learning (ML) algorithms to classify BCUs into BL Lac objects and FSRQs. To address this, we selected the 4LAC-DR3 Clean sample (i.e., sources with no analysis flags) containing 1115 BCUs. We employ five different supervised ML algorithms, namely, random forest, logistic regression, XGBoost, CatBoost, and neural network with seven features: photon index, synchrotron-peak frequency, pivot energy, photon index at pivot energy, fractional variability, ν F ν, at synchrotron-peak frequency, and variability index. Combining results from all models leads to better accuracy and more robust predictions. These five methods together classified 610 BCUs as BL Lac objects and 333 BCUs as FSRQs with a classification metric area under the curve >0.96. Our results are significantly compatible with recent studies as well. The output from this study provides a larger blazar sample with many new targets that could be used for forthcoming multiwavelength surveys. This work can be further extended by adding features in X-rays, UV, visible, and radio wavelengths.

Keywords: active galaxies; blazars; bl lacertae objects; random forests; classification; neural networks