Sazuna/UAT_keywords huggingface dataset:
No Top-heavy Stellar Initial Mass Function Needed: The Ionizing Radiation of GS9422 Can Be Powered by a Mixture of an Active Galactic Nucleus and Stars. JWST is producing high-quality rest-frame optical and UV spectra of faint galaxies at z &gt; 4 for the first time, challenging models of galaxy and stellar populations. One galaxy recently observed at z = 5.943, GS9422, has nebular line and UV continuum emission that appears to require a high ionizing photon production efficiency. This has been explained with an exotic stellar initial mass function (IMF; Cameron et al. 2023a), 10–30x more top-heavy than a Salpeter IMF. Here we suggest an alternate explanation to this exotic IMF. We use a new flexible neural net emulator for CLOUDY, Cue, to infer the shape of the ionizing spectrum directly from the observed emission line fluxes. By describing the ionizing spectrum with a piecewise power law, Cue is agnostic to the source of the ionizing photons. Cue finds that the ionizing radiation from GS9422 can be approximated by a double power law characterized by , which can be interpreted as a combination of young, metal-poor stars and a low-luminosity active galactic nucleus with F  ν  ∝ λ 2 in a 65%/35% ratio. This suggests a significantly lower nebular continuum contribution to the observed UV flux (24%) than a top-heavy IMF (≳80%), and hence, necessitates a damped Lyα absorber to explain the continuum turnover bluewards of ∼1400 Å. While current data cannot rule out either scenario, given the immense impact the proposed top-heavy IMF would have on models of galaxy formation, it is important to propose viable alternative explanations and to further investigate the nature of peculiar high-z nebular emitters.

Keywords: AGN host galaxies, Photoionization, High-redshift galaxies, Interstellar medium
M17 MIR: A Massive Star Is Forming via Episodic Mass Accretion. We analyzed the Atacama Large Millimeter/submillimeter Array (ALMA) band 6 data for the outbursting massive protostar M17 MIR. The ALMA CO J = 2–1 data reveal a collimated and bipolar north–south outflow from M17 MIR. The blueshifted outflow exhibits four CO knots (N1 to N4) along the outflow axis, while the redshifted outflow appears as a single knot (S1). The extremely high velocity (EHV) emissions of N1 and S1 are jetlike and contain subknots along the outflow axis. Assuming the nearest EHV subknots trace the ejecta from the accretion outbursts in the past decades, a tangential ejection velocity of ∼421 km s‑1 is derived for M17 MIR. Assuming the same velocity, the dynamical times of the multiple ejecta, traced by the four blueshifted CO knots, range from 20 to 364 yr. The four blueshifted CO knots imply four clustered accretion outbursts with a duration of tens of years in the past few hundred years. The intervals between the four clustered accretion outbursts are also about tens of years. These properties of the four clustered accretion outbursts are in line with the disk gravitational instability and fragmentation model. The episodic accretion history of M17 MIR traced by episodic outflow suggests that a massive star can form from a lower-mass protostar via frequent episodic accretion events triggered by disk gravitational instability and fragmentation. The first detection of the knotty outflow from an outbursting massive protostar suggests that mass ejections accompanied with accretion events could serve as an effective diagnostic tool for the episodic accretion histories of massive protostars.

Keywords: Stellar jets, Star formation, Stellar accretion
FAST Discovery of Eight Isolated Millisecond Pulsars in NGC 6517. We present the discovery of eight isolated millisecond pulsars in globular cluster (GC) NGC 6517 using the Five-hundred-meter Aperture Spherical radio Telescope (FAST). The spin periods of those pulsars (namely PSR J1801–0857K to R, or NGC 6517K to R) are all shorter than 10 ms. With these discoveries, NGC 6517 is currently the GC with the most known pulsars in the FAST sky. The largest difference in dispersion measure of the pulsars in NGC 6517 is 11.2 cm‑3 pc, the second among all GCs. The fraction of isolated pulsars in this GC (16 of 17, 94%) is consistent with previous studies indicating an overabundance of isolated pulsars in the densest GCs, especially in those undergoing cluster core collapse. Considering the FAST GC pulsar discoveries, we modeled the GC pulsar population using the empirical Bayesian method described by Turk and Lorimer with the recent counts. Using this approach, we find that the expected number of potential pulsars in GCs seems to be correlated with the central escape velocity; hence, the GCs Liller 1, NGC 6441, M54 (NGC 6715), and ω-Cen (NGC 5139) are expected to host the largest numbers of pulsars.

Keywords: Globular star clusters, Millisecond pulsars
A JWST Project on 47 Tucanae: NIRSpec Spectroscopy of Multiple Populations among M Dwarfs. We present the first spectroscopic estimates of the chemical abundance of M dwarf stars in a globular cluster (GC), namely 47 Tucanae. By exploiting NIRSpec on board the James Webb Space Telescope, we gathered low-resolution spectra for 28 stars with masses in the range ∼0.4–0.5 M ⊙. The spectra are strongly affected by the H2O water vapor bands, which can be used as indicators of oxygen abundance. The spectral analysis reveals that the target stars feature a different O abundance, with a difference of ∼0.40 dex between the first and the most polluted second population. The observed range is similar to that observed among red giant stars. This result reinforces previous findings based on the analysis of photometric diagrams, including the "chromosome maps," providing a first, and more direct, evidence of light element variations in the M dwarfs' mass regime. The observation that the multiple populations, with their variations in light elements, exhibit the same patterns from the lower main sequence all the way to the red giant branch further strengthens the notion that multiple stellar populations in GCs formed in a series of bursts of star formation. * The JWST data presented in this article were obtained from the Mikulski Archive for Space Telescopes (MAST) at the Space Telescope Science Institute. The specific observations analyzed can be accessed via doi:10.17909/6t82-4360.

Keywords: Globular star clusters
Shockingly Bright Warm Carbon Monoxide Molecular Features in the Supernova Remnant Cassiopeia A Revealed by JWST. We present JWST NIRCam (F356W and F444W filters) and MIRI (F770W) images and NIRSpec Integral Field Unit (IFU) spectroscopy of the young Galactic supernova remnant Cassiopeia A (Cas A) to probe the physical conditions for molecular CO formation and destruction in supernova ejecta. We obtained the data as part of a JWST survey of Cas A. The NIRCam and MIRI images map the spatial distributions of synchrotron radiation, Ar-rich ejecta, and CO on both large and small scales, revealing remarkably complex structures. The CO emission is stronger at the outer layers than the Ar ejecta, which indicates the re-formation of CO molecules behind the reverse shock. NIRSpec-IFU spectra (3–5.5 μm) were obtained toward two representative knots in the NE and S fields that show very different nucleosynthesis characteristics. Both regions are dominated by the bright fundamental rovibrational band of CO in the two R and P branches, with strong [Ar VI] and relatively weaker, variable strength ejecta lines of [Si IX], [Ca IV], [Ca V], and [Mg IV]. The NIRSpec-IFU data resolve individual ejecta knots and filaments spatially and in velocity space. The fundamental CO band in the JWST spectra reveals unique shapes of CO, showing a few tens of sinusoidal patterns of rovibrational lines with pseudocontinuum underneath, which is attributed to the high-velocity widths of CO lines. Our results with LTE modeling of CO emission indicate a temperature of ∼1080 K and provide unique insight into the correlations between dust, molecules, and highly ionized ejecta in supernovae and have strong ramifications for modeling dust formation that is led by CO cooling in the early Universe.

Keywords: Ejecta, Metal-containing molecules, Astrochemistry, Supernova remnants, Dust formation, James Webb Space Telescope, CO line emission, Supernovae
A NIRCam-dark Galaxy Detected with the MIRI/F1000W Filter in the MIDIS/JADES Hubble Ultra Deep Field. We report the discovery of Cerberus, an extremely red object detected with the MIRI Deep Imaging Survey (MIDIS) observations in the F1000W filter of the Hubble Ultra Deep Field. The object is detected at signal-to-noise ratio (S/N) ∼ 6, with F1000W ∼ 27 mag, and undetected in the NIRCam data gathered by the JWST Advanced Deep Extragalactic Survey (JADES), fainter than the 30.0─30.5 mag 5σ detection limits in individual bands, as well as in the MIDIS F560W ultradeep data (∼29 mag, 5σ). Analyzing the spectral energy distribution built with low-S/N (&lt;5) measurements in individual optical-to-mid-infrared filters and higher-S/N (≳5) measurements in stacked NIRCam data, we discuss the possible nature of this red NIRCam-dark source using a battery of codes. We discard the possibility of Cerberus being a solar system body based on the &lt;0.″016 proper motion in the 1 yr apart JADES and MIDIS observations. A substellar Galactic nature is deemed unlikely, given that the Cerberus's relatively flat NIRCam-to-NIRCam and very red NIRCam-to-MIRI flux ratios are not consistent with any brown dwarf model. The extragalactic nature of Cerberus offers three possibilities: (1) a z ∼ 0.4 galaxy with strong emission from polycyclic aromatic hydrocarbons—the very low inferred stellar mass, M ⋆ = 105─106 M ⊙, makes this possibility highly improbable; (2) a dusty galaxy at z ∼ 4 with an inferred stellar mass M ⋆ ∼ 108 M ⊙; and (3) a galaxy with observational properties similar to those of the reddest little red dots discovered around z ∼ 7, but Cerberus lying at z ∼ 15, with the rest-frame optical dominated by emission from a dusty torus or a dusty starburst.

Keywords: Galaxy formation, Stellar populations, Galaxy ages, James Webb Space Telescope, Active galactic nuclei, Galaxy evolution, Broad band photometry, High-redshift galaxies
SN 2023zaw: An Ultrastripped, Nickel-poor Supernova from a Low-mass Progenitor. We present SN 2023zaw—a subluminous (M  r  = ‑16.7 mag) and rapidly evolving supernova (t 1/2,r  = 4.9 days), with the lowest nickel mass (≈0.002 M ⊙) measured among all stripped-envelope supernovae discovered to date. The photospheric spectra are dominated by broad He I and Ca near-infrared emission lines with velocities of ∼10,000‑12,000 km s‑1. The late-time spectra show prominent narrow He I emission lines at ∼1000 km s‑1, indicative of interaction with He-rich circumstellar material. SN 2023zaw is located in the spiral arm of a star-forming galaxy. We perform radiation-hydrodynamical and analytical modeling of the lightcurve by fitting with a combination of shock-cooling emission and nickel decay. The progenitor has a best-fit envelope mass of ≈0.2 M ☉ and an envelope radius of ≈50 R ⊙. The extremely low nickel mass and low ejecta mass (≈0.5 M ⊙) suggest an ultrastripped SN, which originates from a mass-losing low-mass He-star (zero-age main-sequence mass &lt; 10 M ⊙) in a close binary system. This is a channel to form double neutron star systems, whose merger is detectable with LIGO. SN 2023zaw underscores the existence of a previously undiscovered population of extremely low nickel mass (&lt;0.005 M ☉) stripped-envelope supernovae, which can be explored with deep and high-cadence transient surveys.

Keywords: Core-collapse supernovae, Type Ib supernovae, Compact binary stars, Stellar mass loss, Roche lobe overflow
High-velocity Blue-shifted Fe XXV Heα Line during a Superflare of the RS Canum Venaticorum–type Star IM Peg. The Monitor of All-sky X-ray Image (MAXI) detected a superflare, releasing 5 × 1037 erg in 2‑10 keV, of the RS CVn-type star IM Peg at 10:41 UT on 2023 July 23 with its Gas Slit Camera (2‑30 keV). We conducted X-ray follow-up observations of the superflare with the Neutron Star Interior Composition Explorer (NICER; 0.2‑12 keV) starting at 16:52 UT on July 23 until 06:00 UT on August 2. NICER X-ray spectra clearly showed emission lines of the Fe XXV Heα and Fe XXVI Lyα for ∼1.5 days since the MAXI detection. The Fe XXV Heα line was blueshifted with its maximum Doppler velocity reaching ‑2200 ± 600 km s‑1, suggesting an upward-moving plasma during the flare, such as a coronal mass ejection (CME) and/or chromospheric evaporation. This is the first case that the Fe XXV Heα line is blueshifted during a stellar flare, and its velocity overwhelmingly exceeds the escape velocity of the star (‑230 km s‑1). One hour before the most pronounced blueshift detection, a signature of the reheating of the flare plasma was observed. We discuss the origin of the blueshift, a CME, or high-velocity chromospheric evaporation.

Keywords: X-ray astronomy, Stellar mass loss, Stellar activity, Stellar flares, Stellar coronae
RUBIES: Evolved Stellar Populations with Extended Formation Histories at z ∼ 7–8 in Candidate Massive Galaxies Identified with JWST/NIRSpec. The identification of red, apparently massive galaxies at z &gt; 7 in early James Webb Space Telescope (JWST) photometry suggests a strongly accelerated time line compared to standard models of galaxy growth. A major uncertainty in the interpretation is whether the red colors are caused by evolved stellar populations, dust, or other effects such as emission lines or active galactic nuclei (AGNs). Here we show that three of the massive galaxy candidates at z = 6.7–8.4 have prominent Balmer breaks in JWST/NIRSpec spectroscopy from the RUBIES program. The Balmer breaks demonstrate unambiguously that stellar emission dominates at λ rest = 0.4 μm and require formation histories extending hundreds of millions of years into the past in galaxies only 600–800 Myr after the big bang. Two of the three galaxies also show broad Balmer lines, with Hβ FWHM &gt; 2500 km s‑1, suggesting that dust-reddened AGNs contribute to, or even dominate, the spectral energy distributions of these galaxies at λ rest ≳ 0.6 μm. All three galaxies have relatively narrow [O III] lines, seemingly ruling out a high-mass interpretation if the lines arise in dynamically relaxed, inclined disks. Yet the inferred masses also remain highly uncertain. We model the high-quality spectra using Prospector to decompose the continuum into stellar and AGN components and explore limiting cases in stellar/AGN contribution. This produces a wide range of possible stellar masses, spanning M ⋆ ∼ 109‑1011 M ⊙. Nevertheless, all fits suggest a very early and rapid formation, most of which follow with a truncation in star formation. Potential origins and evolutionary tracks for these objects are discussed, from the cores of massive galaxies to low-mass galaxies with overmassive black holes. Intriguingly, we find all of these explanations to be incomplete; deeper and redder data are needed to understand the physics of these systems.

Keywords: AGN host galaxies, Galaxy formation, Active galactic nuclei, Galaxy evolution, Spectral energy distribution, High-redshift galaxies
Discovery of the Optical and Radio Counterpart to the Fast X-Ray Transient EP 240315a. Fast X-ray Transients (FXTs) are extragalactic bursts of soft X-rays first identified ≳10 yr ago. Since then, nearly 40 events have been discovered, although almost all of these have been recovered from archival Chandra and XMM-Newton data. To date, optical sky surveys and follow-up searches have not revealed any multiwavelength counterparts. The Einstein Probe, launched in 2024 January, has started surveying the sky in the soft X-ray regime (0.5─4 keV) and will rapidly increase the sample of FXTs discovered in real time. Here we report the first discovery of both an optical and radio counterpart to a distant FXT, the fourth source publicly released by the Einstein Probe. We discovered a fast-fading optical transient within the 3' localization radius of EP 240315a with the all-sky optical survey ATLAS, and our follow-up Gemini spectrum provides a redshift, z = 4.859 ± 0.002. Furthermore, we uncovered a radio counterpart in the S band (3.0 GHz) with the MeerKAT radio interferometer. The optical (rest-frame UV) and radio luminosities indicate that the FXT most likely originates from either a long gamma-ray burst or a relativistic tidal disruption event. This may be a fortuitous early mission detection by the Einstein Probe or may signpost a mode of discovery for high-redshift, high-energy transients through soft X-ray surveys, combined with locating multiwavelength counterparts.

Keywords: High energy astrophysics, Optical identification, Relativistic jets, Transient sources, X-ray transient sources, Radio interferometry
The Red Supergiant Progenitor of Type II Supernova 2024ggi. We present a detailed analysis of the progenitor and its local environment for the recently discovered Type II supernova (SN) 2024ggi at a distance of about 6.7 Mpc, by utilizing the pre-explosion images from the Hubble Space Telescope and Spitzer Space Telescope. The progenitor is identified as a red bright variable star, with absolute F814W-band magnitudes being ‑6.2 mag in 1995 to ‑7.2 mag in 2003, respectively, consistent with that of a normal red supergiant star. Combining with the historical mid-infrared light curves, a pulsational period of about 379 days can be inferred for the progenitor star. Fitting its spectral energy distribution with stellar spectral models yields the stellar parameters of temperature, radius, and bolometric luminosity as K, R ⊙, and log(L/L ⊙) , respectively. The above parameters indicate that the progenitor of SN 2024ggi is consistent with the stellar evolutionary track of a solar-metallicity massive star with an initial mass of M ⊙. Moreover, our analysis indicates a relatively low mass-loss rate (i.e., &lt;3 × 10‑6 M ⊙ yr‑1) for the progenitor compared to that inferred from flash spectroscopy and X-ray detection (i.e., 10‑2–10‑5 M ⊙ yr‑1), implying a significant enhancement in mass loss within a few years prior to the explosion.

Keywords: Type II supernovae, Stellar mass loss, Red supergiant stars, Stellar evolution
Carrington Maps in H I Lyα and Their Relationships with Extreme-ultraviolet and Magnetic-field Maps. H I Lyα emission in the chromosphere and transition region is a key ingredient of the incident radiation to coronal neutral hydrogen for modeling corona Lyα emission. The Lyα emission distribution across the solar disk can be obtained from a Lyα Carrington map. Before the launch of the Advanced Space-based Solar Observatory (ASO-S), such a Lyα Carrington map was derived from the Carrington map at He II 30.4 nm and sometimes is even assumed to be uniform. We construct the first Lyα Carrington map based on full-disk Lyα images acquired by the Solar Disk Imager (SDI) on board ASO-S and present two versions: the standard one is for a CR, and the other is daily updated. For modeling Lyα intensities during eruptions, the Carrington map with incorporated flare region is produced. Furthermore, we evaluate the difference between the Lyα Carrington map derived with SDI observations and that synthesized from the 30.4 nm data based on an empirical relationship between Lyα and He II 30.4 nm intensities, particularly extended to flare intensities that have not been investigated before. The average difference of 38% proves the importance of the Lyα Carrington map built from observations directly. However, the synthetic Lyα Carrington map can be used as an approximation before SDI data are available. The comparison between the SDI Lyα Carrington map and the corresponding magnetic field synoptic map indicates that active regions in general are brighter in Lyα, while the sunspot umbras with strong magnetic field strength are usually weaker in Lyα.

Keywords: Solar physics, Solar ultraviolet emission, Astronomy image processing
Extended Emission-line Regions in Poststarburst Galaxies Hosting Tidal Disruption Events. We report the discovery of an extended emission-line region (EELR) in MUSE observations of Markarian 950, a nearby (z = 0.01628) poststarburst (PSB) galaxy that hosted the tidal disruption event (TDE) iPTF 16fnl. The EELR requires a nonstellar ionizing continuum with a luminosity  Lion,min≳1043  erg s−1, inconsistent with the current weak state (L IR,AGN &lt; 2.5 × 1042 erg s−1) of the galactic nucleus. The ionized gas has low velocity (∼─50 km s−1) and low turbulence (σ gas ≲ 50 km s−1) and is kinematically decoupled from the stellar motions, indicating that the gas kinematics is not active galactic nucleus (AGN) driven. Markarian 950 is the third PSB galaxy to host a weak nuclear ionizing source as well as an EELR and a TDE. The overall properties of these three galaxies, including the kinematics and accretion history, are unusual but strikingly similar. We estimate that the incidence of EELRs in PSB-TDE hosts is a factor of ∼10 × higher than in other PSB galaxies. This suggests that a gas-rich postmerger environment is a key ingredient in driving elevated TDE rates. Based on the current observations, we cannot rule out that the EELRs may be powered through an elevated TDE rate in these galaxies. If the EELRs are not TDE powered, the presence of intermittent AGN activity, and in particular the fading of the AGN, may be associated with an increased TDE rate and/or an increased rate of detecting TDEs.

Keywords: Accretion, Tidal disruption, Galaxy mergers
X-Ray View of Little Red Dots: Do They Host Supermassive Black Holes?. The discovery of Little Red Dots (LRDs)—a population of compact, high-redshift, dust-reddened galaxies—is one of the most surprising results from JWST. However, the nature of LRDs is still debated: does the near-infrared emission originate from accreting supermassive black holes (SMBHs), or intense star formation? In this work, we utilize ultra-deep Chandra observations and study LRDs residing behind the lensing galaxy cluster, A2744. We probe the X-ray emission from individual galaxies but find that they remain undetected and provide SMBH mass upper limits of ≲(1.5–16) × 106 M ⊙ assuming Eddington limited accretion. To increase the signal-to-noise ratios, we conduct a stacking analysis of the full sample with a total lensed exposure time of ≈87 Ms. We also bin the galaxies based on their stellar mass, lensing magnification, and detected broad-line Hα emission. For the LRDs exhibiting broad-line Hα emission, there is a hint of a stacked signal (∼2.6σ), corresponding to an SMBH mass of ∼3.2 × 106 M ⊙. Assuming unobscured, Eddington-limited accretion, this black hole (BH) mass is at least 1.5 orders of magnitude lower than that inferred from virial mass estimates using JWST spectra. Given galaxy-dominated stellar mass estimates, our results imply that LRDs do not host overmassive SMBHs and/or accrete at a few percent of their Eddington limit. However, alternative stellar mass estimates may still support that LRDs host overmassive BHs. The significant discrepancy between the JWST and Chandra data hints that the scaling relations used to infer the SMBH mass from the Hα line and virial relations may not be applicable for high-redshift LRDs.

Keywords: Supermassive black holes, James Webb Space Telescope, X-ray active galactic nuclei, Active galactic nuclei