Sazuna/UAT_keywords huggingface dataset:
Systematics in the Cepheid and TRGB Distance Scales: Metallicity Sensitivity of the Wesenheit Leavitt Law. Using an updated and significantly augmented sample of Cepheid and tip of the red giant branch (TRGB) distances to 28 nearby spiral and irregular galaxies, covering a wide range of metallicities, we have searched for evidence of a correlation of the zero-point of the Cepheid period–luminosity relation with H II region (gas-phase) metallicities. Our analysis, for the 21 galaxies closer than 12.5 Mpc, results in the following conclusions: (1) The zero-points of the Cepheid and TRGB distance scales are in remarkably good agreement, with the mean offset in the zero-points of the most nearby distance-selected sample being close to zero, Δμ  o (Cepheid—TRGB) = ‑0.026 ± 0.015 mag (for an I-band TRGB zero-point of M  I  = ‑4.05 mag); however, for the more distant sample, there is a larger offset between the two distance scales, amounting to ‑0.073 ± 0.057 mag &lt;Δμ  o &gt; (Cepheids—TRGB) = ‑0.026 ± 0.015 mag, for an I-band TRGB zero-point of M  I  = ‑4.05 mag. (2) The individual differences, about that mean, have a measured scatter of ±0.068 mag. (3) We find no statistically significant evidence for a metallicity dependence in the Cepheid distance scale using the reddening-free W(V, VI) period–luminosity relation: Δμ  o (Cepheid ‑ TRGB) = ‑ 0.022( ± 0.015) × ([O/H] ‑ 8.50) ‑ 0.003(±0.007).

Keywords: Cepheid variable stars, Metallicity, Red giant branch
Small-scale Magnetic Fields Are Critical to Shaping Solar Gamma-Ray Emission. The Sun is a bright gamma-ray source due to hadronic cosmic-ray interactions with solar gas. While it is known that incoming cosmic rays must generally first be reflected by solar magnetic fields to produce outgoing gamma rays, theoretical models have yet to reproduce the observed spectra. We introduce a simplified model of the solar magnetic fields that captures the main elements relevant to gamma-ray production. These are a flux tube, representing the network elements, and a flux sheet, representing the intergranular sheets. Both the tube and sheet have a horizontal size of order 100 km and serve as sites where cosmic rays are reflected and gamma rays are produced. While our simplified double-structure model does not capture all the complexities of the solar-surface magnetic fields, such as Alfvén turbulence from wave interactions or magnetic fluctuations from convection motions, it improves on previous models by reasonably producing both the hard spectrum seen by Fermi Large Area Telescope at 1–200 GeV and the considerably softer spectrum seen by the High Altitude Water Cherenkov Observatory (HAWC) at near 103 GeV. We show that lower-energy (≲10 GeV) gamma rays are primarily produced in the network elements and higher-energy (≳few × 10 GeV) gamma rays in the intergranular sheets. Notably, the spectrum softening observed by HAWC results from the limited effectiveness of capturing and reflecting ∼104 GeV cosmic rays by the finite-sized intergranular sheets. Our study is important for understanding cosmic-ray transport in the solar atmosphere and will lead to insights into small-scale magnetic fields at the photosphere.

Keywords: Magnetohydrodynamics, Solar photosphere, Galactic cosmic rays, Solar granulation, Solar magnetic fields, Gamma-rays
Monitoring the X-Ray Variability of Bright X-Ray Sources in M33. We present a new five-epoch Chandra X-ray Observatory monitoring survey of the nearby spiral galaxy M33 which probes X-ray variability with time sampling between two weeks and four months. We characterize the X-ray variability of 55 bright point sources outside of the nucleus, many of which are expected to be high-mass X-ray binaries (HMXBs). We detect eight new candidate transients not detected in previous X-ray catalogs of M33 and discuss their possible nature. The final catalog includes 26 known HMXB candidates identified in the literature. We extend the baseline of the X-ray light curves up to 21 yr by including archival X-ray observations of these sources. We compare the detection and nondetection epochs of the sources to suites of simulated source duty cycles and infer that most of our detected sources have duty cycles &gt;30%. We find only four sources whose detection patterns are consistent with having duty cycles below 30%. This large fraction of sources with high duty cycles is unexpected for a population of HMXBs; thus more frequent X-ray monitoring will likely reveal many more low duty cycle HMXBs in M33.

Keywords: X-ray transient sources, Triangulum Galaxy, X-ray point sources, X-ray binary stars
An Extensive Hubble Space Telescope Study of the Offset and Host Light Distributions of Type I Superluminous Supernovae. We present an extensive Hubble Space Telescope rest-frame UV imaging study of the locations of Type I superluminous supernovae (SLSNe) within their host galaxies. The sample includes 65 SLSNe with detected host galaxies in the redshift range z ≈ 0.05─2. Using precise astrometric matching with SN images, we determine the distributions of the physical and host-normalized offsets relative to the host centers, as well as the fractional flux distribution relative to the underlying UV light distributions. We find that the host-normalized offsets of SLSNe roughly track an exponential disk profile, but exhibit an overabundance of sources with large offsets of 1.5─4 times their hosts' half-light radii. The SLSNe normalized offsets are systematically larger than those of long gamma-ray bursts (LGRBs), and even Type Ib/c and Type II SNe. Furthermore, we find from a Monte Carlo procedure that about ${37}_{-8}^{+6} \% $ of SLSNe occur in the dimmest regions of their host galaxies, with a median fractional flux value of 0.16, in stark contrast to LGRBs and Type Ib/c and Type II SNe. We do not detect any significant trends in the locations of SLSNe as a function of redshift, or as a function of explosion and magnetar engine parameters inferred from modeling of their optical light curves. The significant difference in SLSN locations compared to LGRBs (and normal core-collapse SNe) suggests that at least some of their progenitors follow a different evolutionary path. We speculate that SLSNe arise from massive runaway stars from disrupted binary systems, with velocities of ∼102 km s−1.

Keywords: Stellar populations, Supernovae
Could a Kilonova Kill: A Threat Assessment. Binary neutron star mergers produce high-energy emissions from several physically different sources, including a gamma-ray burst (GRB) and its afterglow, a kilonova (KN), and, at late times, a remnant many parsecs in size. Ionizing radiation from these sources can be dangerous for life on Earth-like planets when located too close. Work to date has explored the substantial danger posed by the GRB to on-axis observers; here we focus instead on the potential threats posed to nearby off-axis observers. Our analysis is based largely on observations of the GW170817/GRB 170817A multi-messenger event, as well as theoretical predictions. For baseline KN parameters, we find that the X-ray emission from the afterglow may be lethal out to ∼1 pc and the off-axis gamma-ray emission may threaten a range out to ∼4 pc, whereas the greatest threat comes years after the explosion, from the cosmic rays accelerated by the KN blast, which can be lethal out to distances up to ∼11 pc. The distances quoted here are typical, but the values have significant uncertainties and depend on the viewing angle, ejected mass, and explosion energy in ways we quantify. Assessing the overall threat to Earth-like planets, KNe have a similar kill distance to supernovae, but are far less common. However, our results rely on the scant available KN data, and multi-messenger observations will clarify the danger posed by such events.

Keywords: Nucleosynthesis, X-ray transient sources, Astrobiology, Gamma-ray transient sources, Supernovae, Cosmic rays
The JWST Discovery of the Triply Imaged Type Ia "Supernova H0pe" and Observations of the Galaxy Cluster PLCK G165.7+67.0. A Type Ia supernova (SN) at z = 1.78 was discovered in James Webb Space Telescope Near Infrared Camera imaging of the galaxy cluster PLCK G165.7+67.0 (G165; z = 0.35). The SN is situated 1.5–2 kpc from the host-galaxy nucleus and appears in three different locations as a result of gravitational lensing by G165. These data can yield a value for Hubble's constant using time delays from this multiply imaged SN Ia that we call "SN H0pe." Over the cluster, we identified 21 image multiplicities, confirmed five of them using the Near-Infrared Spectrograph, and constructed a new lens model that gives a total mass within 600 kpc of (2.6 ± 0.3) × 1014 M ⊙. The photometry uncovered a galaxy overdensity coincident with the SN host galaxy. NIRSpec confirmed six member galaxies, four of which surround the SN host galaxy with relative velocity ≲900 km s‑1 and projected physical extent ≲33 kpc. This compact galaxy group is dominated by the SN host galaxy, which has a stellar mass of (5.0 ± 0.1) × 1011 M ⊙. The group members have specific star formation rates of 2–260 Gyr‑1 derived from the Hα-line fluxes corrected for stellar absorption, dust extinction, and slit losses. Another group centered on a strongly lensed dusty star-forming galaxy is at z = 2.24. The total (unobscured and obscured) SFR of this second galaxy group is estimated to be (≳ 100 M ⊙ yr‑1), which translates to a supernova rate of ∼1 SNe yr‑1, suggesting that regular monitoring of this cluster may yield additional SNe.

Keywords: High-redshift galaxy clusters, Galaxy cluster counts, Strong gravitational lensing, Rich galaxy clusters, Galaxy spectroscopy
Panic at the ISCO: Time-varying Double-peaked Broad Lines from Evolving Accretion Disks Are Common among Optically Variable AGNs. About 3%–10% of Type I active galactic nuclei (AGNs) have double-peaked broad Balmer lines in their optical spectra originating from the motion of gas in their accretion disk. Double-peaked profiles arise not only in AGNs, but occasionally appear during optical flares from tidal disruption events and changing-state AGNs. In this paper, we identify 250 double-peaked emitters (DPEs) among a parent sample of optically variable broad-line AGNs in the Zwicky Transient Facility (ZTF) survey, corresponding to a DPE fraction of 19%. We model spectra of the broad Hα emission-line regions and provide a catalog of the fitted accretion disk properties for the 250 DPEs. Analysis of power spectra derived from the 5 yr ZTF light curves finds that DPE light curves have similar amplitudes and power-law indices to other broad-line AGNs. Follow-up spectroscopy of 12 DPEs reveals that ∼50% display significant changes in the relative strengths of their red and blue peaks over long 10–20 yr timescales, indicating that broad-line profile changes arising from spiral arm or hotspot rotation are common among optically variable DPEs. Analysis of the accretion disk parameters derived from spectroscopic modeling provides evidence that DPEs are not in a special accretion state, but are simply normal broad-line AGNs viewed under the right conditions for the accretion disk to be easily visible. We include inspiraling supermassive black hole binary candidate SDSSJ1430+2303 in our analysis, and discuss how its photometric and spectroscopic variability is consistent with the disk-emitting AGN population in the ZTF survey.

Keywords: Radio active galactic nuclei, Tidal disruption, Galaxy accretion disks, Active galactic nuclei
A Large Sample of Extremely Metal-poor Galaxies at z &lt; 1 Identified from the DESI Early Data. Extremely metal-poor galaxies (XMPGs) at relatively low redshift are excellent laboratories for studying galaxy formation and evolution in the early universe. Much effort has been spent on identifying them from large-scale spectroscopic surveys or spectroscopic follow-up observations. Previous work has identified a few hundred XMPGs. In this work, we obtain a large sample of 223 XMPGs at z &lt; 1 from the early data of the Dark Energy Spectroscopic Instrument (DESI). The oxygen abundance is determined using the direct T e method based on the detection of the [O III]λ4363 line. The sample includes 95 confirmed XMPGs based on the oxygen abundance uncertainty; the remaining 128 galaxies are regarded as XMPG candidates. These XMPGs are only 0.01% of the total DESI observed galaxies. Their coordinates and other properties are provided in the paper. The most XMPGs have an oxygen abundance of ∼1/34 Z ⊙, a stellar mass of about 1.5 × 107 M ⊙, and a star formation rate of 0.22 M ⊙ yr‑1. The two most XMPGs present distinct morphologies suggesting different formation mechanisms. The local environmental investigation shows that XMPGs preferentially reside in relatively low-density regions. Many of them fall below the stellar mass–metallicity relations (MZRs) of normal star-forming galaxies. From a comparison of the MZR with theoretical simulations, it appears that XMPGs are good analogs to high-redshift star-forming galaxies. The nature of these XMPG populations will be further investigated in detail with larger and more complete samples from the ongoing DESI survey.

Keywords: Dwarf galaxies, Metallicity, Redshift surveys, Scaling relations
X-Ray Observations of the Enigmatic Wolf─Rayet System θ Mus: Two's Company but Three's a Crowd. θ Mus is a remarkable spectroscopic binary (SB) consisting of a carbon-type Wolf─Rayet star and OV companion (WC6+O6─7V) in a ≈19 days orbit. In addition an O-supergiant is visually detected at a small offset of 46 mas and if gravitationally bound to the SB system would have an orbital period of many decades. θ Mus is X-ray bright and a nonthermal radio source as commonly observed in massive colliding wind (CW) binaries. We present new Chandra X-ray observations of θ Mus, which complement previous XMM-Newton observations. The X-ray emission consists of a cool, nearly steady, weakly absorbed plasma component with broad redshifted emission lines located in an extended region far from the SB system. Hotter plasma is also present traced by Fe XXV emission. The observed flux in the ≈2─5 keV range dropped significantly on a timescale of ≤5 yr. The flux decrease can be attributed to an increase in absorption toward the hotter plasma which is likely located in the confined wind interaction region of the short-period SB system. The X-ray emission of θ Mus is remarkably similar to the WC+O binary γ 2 Vel including carbon recombination spectral lines but both systems show unusual line centroid properties that challenge CW models.

Keywords: Wolf-Rayet stars, Spectroscopic binary stars, X-ray astronomy
Discovery of a Young, Highly Scattered Pulsar PSR J1032-5804 with the Australian Square Kilometre Array Pathfinder. We report the discovery of a young, highly scattered pulsar in a search for highly circularly polarized radio sources as part of the Australian Square Kilometre Array Pathfinder Variables and Slow Transients survey. In follow-up observations with the Parkes radio telescope, Murriyang, we identified PSR J1032−5804 and measured a period of 78.7 ms, a dispersion measure of 819 ± 4 pc cm−3, a rotation measure of −2000 ± 1 rad m−2, and a characteristic age of 34.6 kyr. We found a pulse scattering timescale at 3 GHz of ∼22 ms, implying a timescale at 1 GHz of ∼3845 ms, which is the third most scattered pulsar known and explains its nondetection in previous pulsar surveys. We discuss the identification of a possible pulsar wind nebula and supernova remnant in the pulsar's local environment by analyzing the pulsar spectral energy distribution and the surrounding extended emission from multiwavelength images. Our result highlights the possibility of identifying extremely scattered pulsars from radio continuum images. Ongoing and future large-scale radio continuum surveys will offer us an unprecedented opportunity to find more extreme pulsars (e.g., highly scattered, highly intermittent, and highly accelerated), which will enhance our understanding of the characteristics of pulsars and the interstellar medium.

Keywords: Neutron stars, Interstellar scattering, Galactic radio sources, Radio pulsars
Star Formation in the H II Region Sh2-87: Evidence of Global Hierarchical Collapse. We present a detailed study of the Sh2-87 H II region using a multiwavelength data set in optical to radio bands. A Herschel column density map revealed that the host cloud is filamentary in nature, and together they formed a central dense hub. The extinction map generated using near-infrared photometric data also signifies the nonuniform distribution of the cloud and reveals its filamentary nature. We estimated a sizable variable extinction over the region up to A  V  = 34.4 mag, with an average value of A  V  = 3.4 mag. Using the various infrared color─color criteria, we identified 13 Class I and 202 Class II young stellar objects (YSOs) and 22 Hα-emitting sources toward this region. Further analysis showed that the cluster is mainly composed of low-mass YSOs with a typical age of ∼3 Myr having masses in the range of 0.1─6.0 M ☉. The identified evolved YSOs (i.e., Class II YSOs) are primarily distributed along the filaments and in the outer parts of the cloud, while the recent star formation, inferred by the presence of Class I YSOs, ionized gas, and star-forming clumps, is observed in the hub region. The overall star formation scenario in the Sh2-87 region resembles the global hierarchical collapse model of star formation, where younger massive star formation activity is expected at the central hub along with the distribution of evolved low-mass YSOs in the filaments and the outer parts of the cloud.

Keywords: Star forming regions, Young stellar objects, Pre-main sequence stars, Star formation, Interstellar medium, H II regions
Statistical Association between the Candidate Repeating FRB 20200320A and a Galaxy Group. We present results from angular cross correlations between select samples of CHIME/FRB repeaters and galaxies in three photometric galaxy surveys, which have shown correlations with the first CHIME/FRB catalog containing repeating and nonrepeating sources: Wide-field Infrared Survey Explorer (WISE) × SCOS, DESI-BGS, and DESI-LRG. We find a statistically significant correlation (p-value &lt;0.001, after accounting for look-elsewhere factors) between a sample of repeaters with an extragalactic dispersion measure (DM) &gt; 395 pc cm‑3 and WISE × SCOS galaxies with redshift z &gt; 0.275. We demonstrate that the correlation arises surprisingly because of a statistical association between FRB 20200320A (extragalactic DM ≈ 550 pc cm‑3) and a galaxy group in the same dark matter halo at redshift z ≈ 0.32. We estimate that the host halo, along with an intervening halo at redshift z ≈ 0.12, accounts for at least ∼30% of the extragalactic DM. Our results strongly motivate incorporating galaxy group and cluster catalogs into direct host association pipelines for FRBs with $\lesssim 1^{\prime} $ localization precision, effectively utilizing the two-point information to constrain FRB properties such as their redshift and DM distributions. In addition, we find marginal evidence for a negative correlation at 99.4% confidence limit between a sample of repeating FRBs with baseband data (median extragalactic DM = 354 pc cm‑3) and DESI-LRG galaxies with redshift 0.3 ≤ z &lt; 0.45, suggesting that the repeaters might be more prone than apparent nonrepeaters to propagation effects in FRB–galaxy correlations due to intervening free electrons over angular scales ∼0.°5.

Keywords: Cosmology, Radio transient sources, High energy astrophysics, Large-scale structure of the universe
Exploring X-Ray Properties of Low-metallicity Dwarf Galaxies. One of the primary outstanding questions in extragalactic astronomy is the formation and early evolution of the supermassive black holes that are seen in nearly every massive galaxy. Low-metallicity dwarf galaxies may offer the most representative local analogs to pristine early galaxies, making them a vital tool in probing black hole seed models through the study of the intermediate-mass black holes (IMBHs) possibly hosted therein; though these dwarf galaxies, and the IMBHs they may host, are typically not as well-studied in this context as their higher-metallicity and higher-mass counterparts. In this paper, we explore the X-ray properties of a sample of 37 low-metallicity dwarf galaxies using archival XMM observations, and we compare the properties of this population against a representative sample of higher-metallicity counterparts. We report the detection of 10 sources with 0.3─10 keV luminosity in excess of 1040 erg s−1 within the low-metallicity sample, which we highlight for followup as potential IMBH candidates. Finally, we discuss the differing multiwavelength scaling relations (e.g., L X─L W2, L X─star formation rate) between the two galaxy populations, as well as the sample's L X as a function of metallicity.

Keywords: X-ray astronomy, Dwarf galaxies
Disentangling the Black Hole Mass Spectrum with Photometric Microlensing Surveys. From the formation mechanisms of stars and compact objects to nuclear physics, modern astronomy frequently leverages surveys to understand populations of objects to answer fundamental questions. The population of dark and isolated compact objects in the Galaxy contains critical information related to many of these topics, but is only practically accessible via gravitational microlensing. However, photometric microlensing observables are degenerate for different types of lenses, and one can seldom classify an event as involving either a compact object or stellar lens on its own. To address this difficulty, we apply a Bayesian framework that treats lens type probabilistically and jointly with a lens population model. This method allows lens population characteristics to be inferred despite intrinsic uncertainty in the lens class of any single event. We investigate this method's effectiveness on a simulated ground-based photometric survey in the context of characterizing a hypothetical population of primordial black holes (PBHs) with an average mass of 30M ⊙. On simulated data, our method outperforms current black hole (BH) lens identification pipelines and characterizes different subpopulations of lenses while jointly constraining the PBH contribution to dark matter to ≈25%. Key to robust inference, our method can marginalize over population model uncertainty. We find the lower mass cutoff for stellar origin BHs, a key observable in understanding the BH mass gap, particularly difficult to infer in our simulations. This work lays the foundation for cutting-edge PBH abundance constraints to be extracted from current photometric microlensing surveys.

Keywords: Microlensing parallax, Astrostatistics tools, Bayesian statistics, Black holes, Astrophysical black holes, Astrostatistics techniques, Gravitational microlensing, Dark matter, Primordial black holes
Research on a 44 Day Quasi-periodic Oscillation of Optical Bands for BL Lac S5 0716+714. By means of astronomical observation data from the 60 cm Telescope at Yunnan Observatory, optical data in the g, r, and i bands were collected for BL Lac S5 0716+714, spanning from 2017 November 10 to 2018 May 15. The original data set contains 21,396 quasi-simultaneous multiband points, with 7132 data points for each band. The Lomb–Scargle periodogram method and the weighted wavelet Z-transform method were used to search for a quasi-periodic oscillation (QPO) signal in the data. For the first time, we report a QPO signal at 44 ± 6 days with a final significance of 3.98σ. Further analysis of the spectrum index reveals that the 44 day QPO signal is most likely explained by a helical motion of a blob with velocity β in the jet, where the viewing angle of the emission region in the jet undergoes periodic variations. In addition, we employed the hypothesis testing method (the null hypothesis) to analyze the flux distribution and determined that a double log-normal distribution provides a better fit; thus, there may be two radiative mini-regions within a jet in this source, so this 44 day QPO signal may be superimposed on a longer-term outburst.

Keywords: Non-thermal radiation sources, Relativistic jets, BL Lacertae objects, Astronomy data analysis