adsabs/SciX_UAT_keywords huggingface dataset:
The Discovery of the Faintest Known Milky Way Satellite Using UNIONS

We present the discovery of Ursa Major III/UNIONS 1, the least luminous known satellite of the Milky Way, which is estimated to have an absolute V-band magnitude of $+{2.2}_{-0.3}^{+0.4}$ mag, equivalent to a total stellar mass of ${16}_{-5}^{+6}$ M ⊙. Ursa Major III/UNIONS 1 was uncovered in the deep, wide-field Ultraviolet Near Infrared Optical Northern Survey (UNIONS) and is consistent with an old (τ > 11 Gyr), metal-poor ([Fe/H] ~ -2.2) stellar population at a heliocentric distance of ~10 kpc. Despite its being compact (r h = 3 ± 1 pc) and composed of few stars, we confirm the reality of Ursa Major III/UNIONS 1 with Keck II/DEIMOS follow-up spectroscopy and identify 11 radial velocity members, eight of which have full astrometric data from Gaia and are co-moving based on their proper motions. Based on these 11 radial velocity members, we derive an intrinsic velocity dispersion of ${3.7}_{-1.0}^{+1.4}$ km s-1 but some caveats preclude this value from being interpreted as a direct indicator of the underlying gravitational potential at this time. Primarily, the exclusion of the largest velocity outlier from the member list drops the velocity dispersion to ${1.9}_{-1.1}^{+1.4}$ km s-1, and the subsequent removal of an additional outlier star produces an unresolved velocity dispersion. While the presence of binary stars may be inflating the measurement, the possibility of a significant velocity dispersion makes Ursa Major III/UNIONS 1 a high-priority candidate for multi-epoch spectroscopic follow-ups to deduce the true nature of this incredibly faint satellite.

Keywords: local group; milky way stellar halo; broad band photometry; stellar dynamics
Absolute Calibration of Cepheid Period-Luminosity Relations in NGC 4258

Owing to its accurate distance measured from water-maser motions, NGC 4258 is one of the most important anchors for calibrating the Cepheid period-luminosity relations (PLRs). We expand on previous efforts and carry out a new Cepheid search in this system using the Hubble Space Telescope. We discover and measure a sample of 669 Cepheids in four new and two archival NGC 4258 fields, doubling the number of known Cepheids in this galaxy and obtaining an absolute calibration of their optical PLRs. We determine a Wesenheit (W VI HST) PLR of $-2.574(\pm 0.034)-3.294(\pm 0.042)\mathrm{log}P$ , consistent with an independent Large Magellanic Cloud (LMC) calibration at the level of 0.032 ± 0.044 mag in its zero-point, after accounting for a metallicity dependence of -0.20 ± 0.05 mag dex-1. Our determination of the PLR slope also agrees with the LMC-based value within their uncertainties. We attempt to characterize the metallicity effect of Cepheid PLRs using only the NGC 4258 sample, but a relatively narrow span of abundances limits our sensitivity and yields a W VI HST zero-point dependence of -0.07 ± 0.21 mag dex-1. The Cepheid measurements presented in this study have been used as part of the data to derive the Hubble constant in a companion paper by the SH0ES team.

Keywords: cepheid variable stars; cepheid distance
Early Results from GLASS-JWST. XXIV. The Mass-Metallicity Relation in Lensed Field Galaxies at Cosmic Noon with NIRISS

We present a measurement of the mass-metallicity relation (MZR) at Cosmic Noon, using the JWST near-infrared wide-field slitless spectroscopy obtained by the GLASS-JWST Early Release Science program. By combining the power of JWST and the lensing magnification by the foreground cluster A2744, we extend the measurements of the MZR to the dwarf mass regime at high redshifts. A sample of 50 galaxies with several emission lines is identified across two wide redshift ranges of z = 1.8-2.3 and 2.6-3.4 in the stellar mass range of $\mathrm{log}\,({M}_{* }/{M}_{\odot })\in [6.9,10.0]$ . The observed slope of MZR is 0.223 ± 0.017 and 0.294 ± 0.010 at these two redshift ranges, respectively, consistent with the slopes measured in field galaxies with higher masses. In addition, we assess the impact of the morphological broadening on emission line measurement by comparing two methods of using 2D forward modeling and line profile fitting to 1D extracted spectra. We show that ignoring the morphological broadening effect when deriving line fluxes from grism spectra results in a systematic reduction of flux by ~30% on average. This discrepancy appears to affect all the lines and thus does not lead to significant changes in flux ratio and metallicity measurements. This assessment of the morphological broadening effect using JWST data presents, for the first time, an important guideline for future work deriving galaxy line fluxes from wide-field slitless spectroscopy, such as Euclid, Roman, and the Chinese Space Station Telescope. *Based on observations acquired by JWST under the ERS program ID 1324 (PI: T. Treu).

Keywords: strong gravitational lensing; galaxy photometry; galaxy spectroscopy; dwarf galaxies; high-redshift galaxies; abell clusters; metallicity
The Radio/X-Ray Burst from SGR 1935+2154: Radiation Mechanisms and the Possible QPOs

Recently, a fast radio burst (FRB)-like event was found to be associated with a Galactic magnetar, SGR 1935+2154, accompanied by an X-ray burst. We find this radio burst challenges the typical emission mechanisms involving magnetars, which includes coherent curvature radiation from charged bunches, fast magnetosonic (FMS) waves, synchrotron maser from shocks, and the pulsar-like mechanism for low-twist magnetars. More specifically, we find that (1) the X-rays are most likely to be produced inside the magnetosphere. (2) For the coherent curvature radiation from the decay of the Alfvén wave, it will generally predict a duration (≲0.1 ms) smaller than observations, because of the strong twists of magnetic field lines and the internal damping of Alfvén waves. (3) The FMS wave model predicts a very low emission frequency νp ∼ 0.03 MHz ≪ GHz, unless it is produced inside the magnetosphere. But the absorption effect of the magnetospheric FMS wave model remains to be studied. (4) The synchrotron maser model is challenged because observations show that the peaks in both X-ray and radio light curves are with the same temporal separation ΔtFRB = Δtγ ≈ 0.03 s, while it would predict ΔtFRB ≪ Δtγ. (5) It seems to be difficult to directly apply the low-twist pulsar-like mechanism to flaring magnetars, as magnetar activity can significantly deform the magnetosphere. (6) We suggested four possibilities to study the general properties of FRBs for future observations, especially the possibility of identifying quasi-periodic oscillations with period ∼1-10 ms in double/multiple-peaked FRBs.

Keywords: magnetars; radio transient sources; soft gamma-ray repeaters; magnetospheric radio emissions
Observations of an Unexpected Meteor Shower Outburst at High Ecliptic Southern Latitude and Its Potential Origin

A strong and unexpected meteor shower outburst was observed by the Southern Argentina Agile MEteor Radar Orbital System (SAAMER-OS) at high southern ecliptic latitude within the South Toroidal region. The outburst, which was active throughout solar longitudes 351° and 352°, peaked at 09:30 UT on 2020 March 12, has a mean Sun-centered ecliptic radiant of λ - λ0 ∼ 307°5 and β ∼ -77°2 and a geocentric velocity of 30.7 km s-1. Using the $D^{\prime} $ parameter criterion, we find the corresponding orbital elements of the outburst to match well with both the β Tucanid and δ Mensid meteor showers, suggesting these are in fact the same shower. We also find a promising parent candidate in asteroid (248590) 2006 CS, a large (D ∼ 2 km) highly inclined 52° near-Earth object.

Keywords: meteor showers; meteors; radar astronomy
Faint Stars in a Faint Galaxy. II. The Low-mass Stellar Initial Mass Function of the Boötes I Ultrafaint Dwarf Spheroidal Galaxy

This paper presents improved constraints on the low-mass stellar initial mass function (IMF) of the Boötes I (Boo I) ultrafaint dwarf galaxy, based on our analysis of recent deep imaging from the Hubble Space Telescope. The identification of candidate stellar members of Boo I in the photometric catalog produced from these data was achieved using a Bayesian approach, informed by complementary archival imaging data for the Hubble Ultra Deep Field. Additionally, the existence of earlier-epoch data for the fields in Boo I allowed us to derive proper motions for a subset of the sources and thus identify and remove likely Milky Way stars. We were also able to determine the absolute proper motion of Boo I, and our result is in agreement with, but completely independent of, the measurement(s) by Gaia. The best-fitting parameter values of three different forms of the low-mass IMF were then obtained through forward modeling of the color-magnitude data for likely Boo I member stars within an approximate Bayesian computation Markov Chain Monte Carlo algorithm. The best-fitting single power-law IMF slope is $\alpha =-{1.95}_{-0.28}^{+0.32}$ , while the best-fitting broken power-law slopes are ${\alpha }_{1}=-{1.67}_{-0.57}^{+0.48}$ and ${\alpha }_{2}=-{2.57}_{-1.04}^{+0.93}$ . The best-fitting lognormal characteristic mass and width parameters are ${M}_{c}={0.17}_{-0.11}^{+0.05}{{ \mathcal M }}_{\odot }$ and $\sigma ={0.49}_{-0.20}^{+0.13}$ . These broken power-law and lognormal IMF parameters for Boo I are consistent with published results for the stars within the Milky Way, and thus it is plausible that Boötes I and the Milky Way are populated by the same stellar IMF.

Keywords: initial mass function; space astrometry; low mass stars; proper motions; dwarf spheroidal galaxies
Hiding Planets Near and Far: The Parameter Space of Hidden Companions for Known Planetary Systems

Recent ground- and space-based observations show that stars with multiple planets are common in the Galaxy. Most of these observational methods are biased toward detecting large planets near to their host stars. Because of these observational biases, these systems can hide small, close-in planets or far-orbiting (big or small) companions. These planets can still exert dynamical influence on known planets and have such influence exerted on them in turn. In certain configurations, this influence can destabilize the system; in others, the star's gravitational influence can instead further stabilize the system. For example, in systems with planets close to the host star, effects arising from general relativity can help to stabilize the configuration. We derive criteria for hidden planets orbiting both beyond and within known planets that quantify how strongly general relativistic effects can stabilize systems that would otherwise be unstable. As a proof of concept, we investigate the several planets in a system based on Kepler-56 and show that the outermost planet will not disrupt the system even at high eccentricities, and we show that an Earth-radius planet could be stable within this system if it orbits below 0.08 au. Furthermore, we provide specific predictions to known observed systems by constraining the parameter space of possible hidden planets.

Keywords: dynamical evolution; exoplanet dynamics; general relativity; planetary dynamics; star-planet interactions
Optimizing Numerical Simulations of Colliding Galaxies. II. Comparing Simulations to Astronomical Observations

Our research focuses on determining the dynamical orbital parameters associated with galaxy collisions. We are accomplishing this by optimizing numerical models of galactic interactions with astronomical observations of colliding galaxies and measuring the uncertainty in the parameter space of these models. This paper will focus on how we compare our numerical models to observed colliding galaxies. We create gravitational n-body models that capture the tidal distortions from galaxy collisions. The final particle positions are then processed to create model images that have realistic intensity profiles and resolutions. We compare the model's output with the astronomical images to obtain an objective machine score that should reflect the fitness of the model. To test our scoring methods, we then compare our machine scores to the human-scores obtained from the citizen science project Galaxy Zoo: Mergers.

Keywords: cosmology; astronomical simulations; galaxy collisions; galaxy interactions; galaxy mergers
Intrinsic Morphology of Ultra-diffuse Galaxies

With the published data of apparent axis ratios for 1109 ultra-diffuse galaxies (UDGs) located in 17 low-redshift (z ∼ 0.020-0.063) galaxy clusters and 84 UDGs in two intermediate-redshift (z ∼ 0.308-0.348) clusters, we take advantage of a Markov Chain Monte Carlo approach and assume a triaxial model to investigate the intrinsic morphologies of UDGs. In contrast to the conclusion of Burkert, i.e., the underlying shapes of UDGs are purely prolate (C = B < A), we find that the data favor the oblate-triaxial models (i.e., thick disks with $C\lt B\lesssim A$ ) over the nearly prolate ones. We also find that the intrinsic morphologies of UDGs are related to their stellar masses/luminosities, environments, and redshifts. First, the more luminous UDGs have puffier morphologies compared with the less luminous counterparts; the UDG morphologic dependence on luminosity is distinct from that of the typical quiescent dwarf ellipticals (dEs) and dwarf spheroidals (dSphs); in this sense, UDGs may not be simply treated as an extension of the dE/dSph class with similar evolutionary histories; they may differ not only in size. Second, the UDGs with smaller clustercentric distances are more puffed up, compared with the counterparts with larger clustercentric distances; in combination with the UDG thickness dependence on luminosity, the puffier morphologies of UDGs with high luminosities or located in the denser environments are very likely to be attributed to tidal interactions with massive galaxies. Third, we find that the intermediate-redshift UDGs are more flattened, compared with the low-redshift counterparts, which plausibly suggests a "disky" origin for the high-redshift, newly born UDGs.

Keywords: dwarf galaxies; galaxy evolution; galaxy photometry
Catalog of Long-term Transient Sources in the First 10 yr of Fermi-LAT Data

We present the first Fermi Large Area Telescope (LAT) catalog of long-term γ-ray transient sources (1FLT). This comprises sources that were detected on monthly time intervals during the first decade of Fermi-LAT operations. The monthly timescale allows us to identify transient and variable sources that were not yet reported in other Fermi-LAT catalogs. The monthly data sets were analyzed using a wavelet-based source detection algorithm that provided the candidate new transient sources. The search was limited to the extragalactic regions of the sky to avoid the dominance of the Galactic diffuse emission at low Galactic latitudes. The transient candidates were then analyzed using the standard Fermi-LAT maximum likelihood analysis method. All sources detected with a statistical significance above 4σ in at least one monthly bin were listed in the final catalog. The 1FLT catalog contains 142 transient γ-ray sources that are not included in the 4FGL-DR2 catalog. Many of these sources (102) have been confidently associated with active galactic nuclei (AGNs): 24 are associated with flat-spectrum radio quasars, 1 with a BL Lac object, 70 with blazars of uncertain type, 3 with radio galaxies, 1 with a compact steep-spectrum radio source, 1 with a steep-spectrum radio quasar, and 2 with AGNs of other types. The remaining 40 sources have no candidate counterparts at other wavelengths. The median γ-ray spectral index of the 1FLT-AGN sources is softer than that reported in the latest Fermi-LAT AGN general catalog. This result is consistent with the hypothesis that detection of the softest γ-ray emitters is less efficient when the data are integrated over year-long intervals.

Keywords: high energy astrophysics; active galactic nuclei; gamma-ray bursts; solar flares; solar gamma-ray emission; gamma-rays; gamma-ray sources; catalogs; gamma-ray telescopes; gamma-ray transient sources; blazars; quasars
JWST Observations Reject Unrecognized Crowding of Cepheid Photometry as an Explanation for the Hubble Tension at 8σ Confidence

We present high-definition observations with the James Webb Space Telescope (JWST) of >1000 Cepheids in a geometric anchor of the distance ladder, NGC 4258, and in five hosts of eight Type Ia supernovae, a far greater sample than previous studies with JWST. These galaxies individually contain the largest samples of Cepheids, an average of >150 each, producing the strongest statistical comparison to those previously measured with the Hubble Space Telescope (HST) in the near-infrared (NIR). They also span the distance range of those used to determine the Hubble constant with HST, allowing us to search for a distance-dependent bias in HST measurements. The superior resolution of JWST negates crowding noise, the largest source of variance in the NIR Cepheid period–luminosity relations (Leavitt laws) measured with HST. Together with the use of two epochs to constrain Cepheid phases and three filters to remove reddening, we reduce the dispersion in the Cepheid P–L relations by a factor of 2.5. We find no significant difference in the mean distance measurements determined from HST and JWST, with a formal difference of ‑0.01 ± 0.03 mag. This result is independent of zero-points and analysis variants including metallicity dependence, local crowding, choice of filters, and slope of the relations. We can reject the hypothesis of unrecognized crowding of Cepheid photometry from HST that grows with distance as the cause of the "Hubble tension" at 8.2σ, i.e., greater confidence than that of the Hubble tension itself. We conclude that errors in photometric measurements of Cepheids across the distance ladder do not significantly contribute to the tension.

Keywords: hubble constant
Global Circulation of the Open Magnetic Flux of the Sun

The global circulation of the open magnetic flux of the Sun, the component of the solar magnetic field that opens into the heliosphere, and the consequences of the global circulation were proposed by Fisk and coworkers in the early 2000s. The Parker Solar Probe, on its initial encounters with the Sun, has provided direct confirmation of both the global circulation and the physical mechanism by which the circulation occurs, transport by interchange reconnection between open magnetic flux and large coronal loops. The implications of this confirmation of the global circulation of open magnetic flux and the importance of interchange reconnection is discussed.

Keywords: solar magnetic fields; solar wind; solar coronal loops
Identifying High-energy Neutrino Transients by Neutrino Multiplet-triggered Follow-ups

Transient sources such as supernovae (SNe) and tidal disruption events are candidates of high-energy neutrino sources. However, SNe commonly occur in the universe and a chance coincidence of their detection with a neutrino signal cannot be avoided, which may lead to a challenge of claiming their association with neutrino emission. In order to overcome this difficulty, we propose a search for ~10-100 TeV multiple neutrino events within a timescale of ~30 days coming from the same direction, called neutrino multiplets. We show that demanding multiplet detection by a ~1 km3 neutrino telescope limits the distances of detectable neutrino sources, which enables us to identify source counterparts by multiwavelength observations owing to the substantially reduced rate of the chance coincidence detection of transients. We apply our results by constructing a feasible strategy for optical follow-up observations and demonstrate that wide-field optical telescopes with a ≳4 m dish should be capable of identifying a transient associated with a neutrino multiplet. We also present the resultant sensitivity of multiplet neutrino detection as a function of the released energy of neutrinos and burst rate density. A model of neutrino transient sources with an emission energy greater than a few × 1051 erg and a burst rate rarer than a few ×10-8 Mpc-3 yr-1 is constrained by the null detection of multiplets by a ~1 km3 scale neutrino telescope. This already disfavors the canonical high-luminosity gamma-ray bursts and jetted tidal disruption events as major sources in the TeV-energy neutrino sky.

Keywords: neutrino astronomy; particle astrophysics; high energy astrophysics; cosmic ray sources; supernovae
How Does the Polar Dust Affect the Correlation between Dust Covering Factor and Eddington Ratio in Type 1 Quasars Selected from the Sloan Digital Sky Survey Data Release 16?

We revisit the dependence of the covering factor (CF) of dust torus on physical properties of active galactic nuclei (AGNs) by taking into account an AGN polar dust emission. The CF is converted from a ratio of infrared (IR) luminosity contributed from AGN dust torus ( ${L}_{\mathrm{IR}}^{\mathrm{torus}}$ ) and AGN bolometric luminosity (Lbol), by assuming a nonlinear relation between luminosity ratio and intrinsic CF. We select 37,181 type 1 quasars at z < 0.7 from the Sloan Digital Sky Survey Data Release 16 quasar catalog. Their Lbol, black hole mass (MBH), and Eddington ratio (λEdd) are derived by spectral fitting with QSFit. We conduct spectral energy distribution decomposition by using X-CIGALE with a clumpy torus and polar dust model to estimate ${L}_{\mathrm{IR}}^{\mathrm{torus}}$ without being affected by the contribution of stellar and AGN polar dust to IR emission. For 5752 quasars whose physical quantities are securely determined, we perform a correlation analysis on CF and (i) Lbol, (ii) MBH, and (iii) λEdd. As a result, anticorrelations for CF-Lbol, CF-MBH, and CF-λEdd are confirmed. We find that incorporating the AGN polar dust emission makes those anticorrelations stronger compared to those without considering it. This indicates that polar dust wind probably driven by AGN radiative pressure is one of the key components to regulate obscuring material of AGNs.

Keywords: quasars; supermassive black holes; catalogs
Novel Correlations between Diffuse Interstellar Bands and Optical Reddening

The relatively new and expansive Apache Point Observatory Catalog of Optical Diffuse Interstellar Bands was analyzed to identify novel correlations between diffuse interstellar bands (DIBs) and optical reddening E(B - V), with a principal aim being to facilitate future identifications of the host molecular carriers. The following lines exhibit the highest Pearson r correlations in descending order (0.930 ≥ r ≥ 0.885), and are tied to DIBs featuring n ≥ 10 sightlines and possessing equivalent width uncertainties: λ (Å) ≃ 5236.27, 5793.24, 5797.18, 6449.27, 6795.26, 5948.87, 6113.22, 6860.02, 6059.34, 6520.74. Independent observations to confirm the preliminary trends are desirable, and extinction estimates could be subsequently inferred for targets by relying on longer-wavelength (NIR) photometric calibrations linked to a weighted subset of numerous DIBs. Lastly, several DIBs appear unassociated with E(B - V), thereby reaffirming that diverse carriers exist.

Keywords: interstellar reddening; diffuse interstellar bands; interstellar medium; astrochemistry