Sazuna/UAT_keywords huggingface dataset:
High-resolution BOES Spectroscopy of Raman-scattered He IIλ6545 in Young Planetary Nebulae. Young planetary nebulae (PNe) are characterized by their hot central stars and the presence of abundant neutral and molecular components, which result from significant mass loss during the asymptotic giant branch phase of stellar evolution. Far-UV He IIλ1025 line photons produced near the central star can undergo Raman scattering by hydrogen atoms, creating a broad emission feature centered at ~6545 Å. We conducted high-resolution spectroscopy of 12 young PNe from 2019 April to 2020 March using the Bohyunsan Observatory Echelle Spectrograph. Building on the study by Choi and Lee, who identified Raman-scattered He II at 6545 Å in NGC 6881 and NGC 6886, we report new detections of this feature in NGC 6741 and NGC 6884. Profile fitting reveals that the velocity of the H I component relative to the He II emission region ranges from 26 to 33 km s‑1 in these PNe. Using photoionization modeling, we estimate the line flux of He IIλ1025 and derive Raman conversion efficiencies of 0.39, 0.21, 0.24, and 0.07 for NGC 6881, NGC 6741, NGC 6886, and NGC 6884, respectively. These results, combined with radiative transfer modeling, suggest the presence of H I components with masses around 10‑2M⊙, moving outward from the central He II emission region at speeds characteristic of the slow stellar wind from a mass-losing giant star.

Keywords: High resolution spectroscopy, Planetary nebulae, Radiative transfer, Stellar mass loss
Exploring Variation of Double-peak Broad-line Profile in Strongly Variable AGNs. The geometry and kinematics of the broad-line region (BLR) in active galactic nuclei (AGNs) are still unclear, which is crucial for studying the physics and evolution of supermassive black holes and AGNs. The broad-line profile provides valuable information on BLR geometry and kinematics. In this work, we explore the evolution of line profiles in variable AGNs based on the BLR model of Czerny and Hryniewicz, where the BLR is driven by the radiation pressure acting on dust at the surface layers of the accretion disk. The line profiles in the low-Eddington-ratio regime show a double-peak profile, which will become a single peak at high Eddington ratios. The high metallicity of Z ≳ 5 Z⊙ is required to reproduce the observational anticorrelation between the peak separation of broad lines and the Eddington ratio for a sample of AGNs. For the broad lines in variable AGNs, it will take several years to several decades to change their line profile if the disk luminosity suffers strong variation in a much shorter timescale. More monitoring of the broad line and continuum in strongly variable AGNs can shed special light on BLR physics.

Keywords: Accretion, Supermassive black holes, Active galactic nuclei, Quasars
Radial-dependent Responsivity of Broad-line Regions in Active Galactic Nuclei: Observational Consequences for Reverberation Mapping and Black Hole Mass Measurements. The reverberation mapping (RM) technique has seen wide applications in probing geometry and kinematics of broad-line regions (BLRs) and measuring masses of supermassive black holes (SMBHs) in active galactic nuclei. However, key quantities in RM analysis such as emissivity, responsivity, transfer functions, and mean and rms spectra are fragmentally defined in the literature and largely lack a unified formulation. Here we establish a rigorous framework for BLR RM and include a locally dependent responsivity according to photoionization calculations. The mean and rms spectra are analytically expressed with emissivity- and responsivity-weighted transfer functions, respectively. We demonstrate that the rms spectrum is proportional to the responsivity-weighted transfer function only when the continuum variation timescale is much longer than the typical extension in time delay of the BLR; otherwise, biases arise in the obtained rms line widths. The long-standing phenomenon pertaining to the different shapes between the mean and rms spectra can be explained by a radial-increasing responsivity of BLRs. The debate on the choice of emission-line widths for SMBH mass measurements is explored, and the virial factors are suggested to also depend on the luminosity states, in addition to the geometry and kinematics of BLRs.

Keywords: Supermassive black holes, Reverberation mapping, Active galactic nuclei
Physical Pathways for JWST-observed Supermassive Black Holes in the Early Universe. Observations with the James Webb Space Telescope (JWST) have revealed active galactic nuclei (AGN) powered by supermassive black holes (SMBHs) with estimated masses of 107–108 M⊙ at redshifts z ∼ 7–9. Some reside in overmassive systems with higher AGN to stellar mass ratios than locally. Understanding how massive black holes could form so early in cosmic history and affect their environment to establish the observed relations today are some of the major open questions in astrophysics and cosmology. One model to create these massive objects is through direct collapse black holes (DCBHs) that provide massive seeds (∼105–106 M⊙), able to reach high masses in the limited time available. We use the cosmological simulation code GIZMO to study the formation and growth of DCBH seeds in the early Universe. To grow the DCBHs, we implement a gas swallowing model set to match the Eddington accretion rate as long as the nearby gaseous environment, affected by stellar and accretion disk feedback, provides sufficient fuel. We find that to create massive AGN in overmassive systems at high redshifts, massive seeds accreting more efficiently than the fiducial Bondi–Hoyle model are needed. We assess whether the conditions for such enhanced accretion rates are realistic by considering limits on plausible transport mechanisms. We also examine various DCBH growth histories and find that mass growth is more sustained in overdense cosmological environments, where high gas densities are achieved locally. We discuss the exciting prospect to directly probe the assembly history of the first SMBHs with upcoming, ultradeep JWST surveys.

Keywords: Early universe, Galaxy formation, Supermassive black holes, Theoretical models, Active galactic nuclei
Simulations of Eccentricity Growth in Compact Binary Accretion Disks with Magnetohydrodynamic Turbulence. We present the results of four magnetohydrodynamic simulations and one alpha-disk simulation of accretion disks in a compact binary system, neglecting vertical stratification and assuming a locally isothermal equation of state. We demonstrate that in the presence of a net vertical field, disks that extend out to the 3:1 mean-motion resonance grow eccentricity in full MHD in much the same way as in hydrodynamical disks. Hence, turbulence due to the magnetorotational instability (MRI) does not impede the tidally driven growth of eccentricity in any meaningful way. However, we find two important differences with alpha-disk theory. First, in MHD, eccentricity builds up in the inner disk with a series of episodes of radial disk-breaking into two misaligned eccentric disks, separated by a region of circular orbits. Standing eccentric waves are often present in the inner eccentric disk. Second, the successful spreading of an accretion disk with MRI turbulence out to the resonant radius is nontrivial—and much harder than spreading an alpha disk. This is due to the tendency to develop overdense rings in which tidal torques overwhelm MRI transport and truncate the disk too early. We believe that the inability to spread the disk sufficiently was the reason why our previous attempt to excite eccentricity via the 3:1 mean-motion resonance with MHD failed. Exactly how MHD disks successfully spread outward in compact binary systems is an important problem that has not yet been understood.

Keywords: Stellar accretion disks, Magnetohydrodynamics, Cataclysmic variable stars
Figuring Out Gas and Galaxies In Enzo (FOGGIE). VIII. Complex and Stochastic Metallicity Gradients at z &gt; 2. Gas-phase metallicity gradients are a crucial element in understanding the chemical evolution of galaxies. We use the FOGGIE simulations to study the metallicity gradients (∇Z) of six Milky Way–like galaxies throughout their evolution. FOGGIE galaxies generally exhibit steep negative gradients for most of their history, with only a few short-lived instances reaching positive slopes that appear to arise mainly from interactions with other galaxies. FOGGIE concurs with other simulation results but disagrees with the robust observational finding that flat and positive gradients are common at z &gt; 1. By tracking the metallicity gradient at a rapid cadence of simulation outputs (∼5–10 Myr), we find that theoretical gradients are highly stochastic: the FOGGIE galaxies spend ∼30%–50% of their time far away from a smoothed trajectory inferred from analytic models or other, less high-cadence simulations. This rapid variation makes instantaneous gradients from observations more difficult to interpret in terms of physical processes. Because of these geometric and stochastic complications, we explore nonparametric methods of quantifying the evolving metallicity distribution at z &gt; 1. We investigate how efficiently nonparametric measures of the 2D metallicity distribution respond to metal production and mixing. Our results suggest that new methods of quantifying and interpreting gas-phase metallicity will be needed to relate trends in upcoming high-z James Webb Space Telescope observations with the underlying physics of gas accretion, expulsion, and recycling in early galaxies.

Keywords: Chemical abundances, Metallicity, Galaxy evolution, Galaxy chemical evolution
Chandra Follow-up Observations of Swift-BAT-selected AGNs III. The cosmic X-ray background (CXB) is dominated by the obscured and unobscured coronal light of active galactic nuclei (AGN). At energies below 10 keV, the CXB can be well explained by models taking into account the known AGN and the observed distribution of their obscuring, line-of-sight column densities, NH,l.o.s. However, at energies around the Compton reflection hump (~30 keV), the models fall short of the data. This suggests the existence of a population of as yet undetected Compton-thick (CT) AGN (NH,l.o.s &gt; 1.5 × 1024 cm‑2) whose X-ray spectra are dominated by the light that has been reprocessed by the obscuring material. In this work, we continue the effort to find and catalog all local (z &lt; 0.05) CT AGN. To this end, we obtained soft X-ray data with Chandra for six local BAT detected sources lacking ROSAT (0.1–2.4 keV) counterparts, indicating potential obscuration. We fit their spectra with Bayesian and least squares methods using two different models, borus02 and UXCLUMPY. We compare the results of the different models and methods and find that the NH,l.o.s is consistently measured in each case. Three of the sources were also observed with XMM-Newton, allowing the opportunity to search for variability in soft X-ray flux or NH,l.o.s. From this sample, we find one strong CT candidate (NGC 5759) and one weaker CT candidate (CGCG 1822.3+2053). Furthermore, we find tentative evidence of NH,l.o.s variability in 2MASX J17253053–4510279, which has NH,l.o.s &lt; 1022 cm‑2.

Keywords: Seyfert galaxies, X-ray active galactic nuclei, Active galactic nuclei, X-ray astronomy
Reverberation Mapping of Two Variable Active Galactic Nuclei: Probing the Distinct Characteristics of the Inner and Outer Broad-line Regions. Current reverberation mapping (RM) studies primarily focus on single emission lines, particularly the Hβ line, which may not fully reveal the geometry and kinematic properties of the broad-line region (BLR). To overcome this limitation, we have conducted multiline RM observations on two highly variable active galactic nuclei (AGNs), KUG 1141+371 and UGC 3374, using the Lijiang 2.4 m telescope. Our goal was to investigate the detailed structures of different regions within the BLR. We measured the time lags of multiple broad emission lines (Hα, Hβ, Hγ, He I, and He II) and found clear evidence of radial ionization stratification in the BLRs of both AGNs. Velocity-resolved RM analysis revealed distinct geometry and kinematics between the inner and outer regions of the BLRs. Assuming that the velocity-resolved lags reflect the kinematics of the BLR, our observations indicate that: (1) in KUG 1141+371, the inner BLR exhibits outflow signatures, while the outer region is consistent with virialized motion; and (2) in UGC 3374, the inner region displays virial motion, while the outer region shows inflow. Furthermore, we detected "breathing" behavior in the outer BLR regions of both AGNs, while the inner BLR regions show "anti-breathing," which may be linked to intrinsic BLR properties. We discuss these findings in the context of various BLR formation models, highlighting the importance of long-term, multiline RM campaigns in understanding of BLR structure and evolution. Additionally, our results suggest that the observed stratification in BLR geometry and kinematics may contribute to the scatter in black hole mass estimates and the rapid changes in velocity-resolved RM signatures reported in recent studies.

Keywords: Supermassive black holes, Reverberation mapping, Seyfert galaxies, Active galactic nuclei, Time domain astronomy
Finding Lensed Radio Sources with the Very Large Array Sky Survey. Radio observations of strongly lensed objects are valuable as cosmological probes. Lensed radio sources have proven difficult to identify, in large part due to the limited depth and angular resolution of the previous generation of radio sky surveys, and, as such, only a few dozen lensed radio sources are known. In this work, we present the results of a pilot study, using the Very Large Array Sky Survey (VLASS) in combination with optical data to more efficiently identify lensed radio sources. We obtain high-resolution (0 2) VLA follow-up observations for 11 targets that we identify using three different techniques: (i) a search for compact radio sources offset from galaxies with high lensing potential, (ii) VLASS detections of known lensed galaxies, and (iii) VLASS detections of known lensed quasars. Five of our targets show radio emission from the lensed images, including 100% of the lensed optical quasar systems. This work demonstrates the efficacy of combining deep- and high-resolution wide-area radio and optical survey data to efficiently find lensed radio sources, and we discuss the potential impact of such an approach using next-generation surveys with the Vera C. Rubin Observatory, Euclid, and Nancy Grace Roman Space Telescope.

Keywords: Radio active galactic nuclei, Galaxy dark matter halos, Strong gravitational lensing, Surveys
Tides on Lava Worlds: Application to Close-in Exoplanets and the Early Earth–Moon System. Understanding the physics of planetary magma oceans has been the subject of growing efforts, in light of the increasing abundance of solar system samples and extrasolar surveys. A rocky planet harboring such an ocean is likely to interact tidally with its host star, planetary companions, or satellites. To date, however, models of the tidal response and heat generation of magma oceans have been restricted to the framework of weakly viscous solids, ignoring the dynamical fluid behavior of the ocean beyond a critical melt fraction. Here we provide a handy analytical model that accommodates this phase transition, allowing for a physical estimation of the tidal response of lava worlds. We apply the model in two settings: the tidal history of the early Earth–Moon system in the aftermath of the giant impact, and the tidal interplay between short-period exoplanets and their host stars. For the former, we show that the fluid behavior of the Earth's molten surface drives efficient early lunar recession to ~25 Earth radii within 104–105 yr, in contrast with earlier predictions. For close-in exoplanets, we report on how their molten surfaces significantly change their spin–orbit dynamics, allowing them to evade spin–orbit resonances and accelerating their track toward tidal synchronization from a gigayear to megayear timescale. Moreover, we reevaluate the energy budgets of detected close-in exoplanets, highlighting how the surface thermodynamics of these planets are likely controlled by enhanced, fluid-driven tidal heating, rather than vigorous insolation, and how this regime change substantially alters predictions for their surface temperatures.

Keywords: Extrasolar rocky planets, The Moon, Earth (planet), Exoplanet evolution, Exoplanet tides, Exoplanet structure, Star-planet interactions
Can Active Galactic Nuclei Activity Be Enhanced by Ram Pressure Stripping?—X-Ray Perspective. Ram pressure stripping (RPS) is an important process that plays a significant role in shaping the evolution of cluster galaxies and their surrounding environment. Despite its recognized significance, the potential connection between RPS and active galactic nuclei (AGN) activity in cluster galaxies remains poorly understood. Recent claims, based on optical emission-line diagnostics, have suggested such a connection. Here, we investigate this relationship from an X-ray perspective, using a sample of galaxies undergoing RPS in four nearby galaxy clusters: A1656, A1367, A426, and A3627. This study is the first to test such a connection from an X-ray standpoint. Our analysis reveals no signs of enhanced X-ray AGN activity in our sample, with most RPS galaxies (~90%) showing X-ray luminosities below 1041 erg s‑1 in their central point sources. Moreover, there is no noticeable difference in X-ray AGN activity among RPS galaxies compared to a control sample of non-RPS galaxies, as demonstrated by the similar X-ray luminosities observed in their central point sources. While the most luminous X-ray AGN in our sample is found in ESO 137-002, a galaxy undergoing RPS in A3627, there is no evidence for a widespread enhancement of X-ray AGN activity due to RPS. Given the limited sample size of our study, this could also indicate that either the X-ray AGN enhancement from RPS is at most weak or the timescale for the X-ray AGN enhancement is short. This emphasizes the need for further investigations with larger X-ray samples to better understand the impact of RPS on AGN activity in cluster galaxies.

Keywords: Galaxy clusters, AGN host galaxies, Galaxy environments, Ram pressure stripped tails, X-ray active galactic nuclei, Galaxy evolution, Intracluster medium, Galaxies
Testing the Breakdown of the Asteroseismic Scaling Relations in Luminous Red Giants. Nearly all cool, evolved stars are solar-like oscillators, and fundamental stellar properties can be inferred from these oscillations with asteroseismology. Scaling relations are commonly used to relate global asteroseismic properties—the frequency of maximum power   and the large-frequency separation Δν—to stellar properties. Mass, radius, and age can then be inferred with the addition of stellar spectroscopy. There is excellent agreement between seismic radii and fundamental data on the lower red giant branch and red clump. However, the scaling relations appear to breakdown in luminous red-giant stars. We attempt to constrain the contributions of the asteroseismic parameters to the observed breakdown. We test the   and Δν scaling relations separately, by using stars of known mass and radius in star clusters and the Milky Way's high-α sequence. We find evidence that the Δν scaling relation contributes to the observed breakdown in luminous giants more than the   relation. We test different methods of mapping the observed Δν to the mean density via a correction factor, FΔν, and find a ≈ 1%–3% difference in the radii in the luminous giant regime, depending on the technique used to measure FΔν. The differences between the radii inferred by these two techniques are too small on the luminous giant branch to account for the inflated seismic radii observed in evolved giant stars. Finally, we find that the FΔν correction is insensitive to the adopted mixing length, chosen by calibrating the models to observations of Teff .

Keywords: Stellar pulsations, Stellar populations, Red giant stars, Asteroseismology, Stellar evolution
What Does the LMC Look Like? It Depends on [M/H] and Age. We offer a new way to look at the LMC through stellar mono-abundance and mono-age mono-abundance maps. These maps are based on ≳500,000 member stars with estimates of [M/H] (σ[M/H] ~ 0.17) and age  ), derived from Gaia Data Release 3 XP spectra and photometry, which are tied to and validated against APOGEE. This results in the first area-complete, metallicity- and age-differentiated stellar maps of any disk galaxy. Azimuthally averaged, these maps reveal a surprisingly simple picture of the Milky Way's largest satellite galaxy. For any [M/H] below ‑0.1 dex, the LMC's radial profile is well described by a simple exponential, but with a scale length that steadily shrinks toward higher metallicities, from nearly 2.3 kpc at [M/H] = ‑1.8 to only 0.75 kpc at [M/H] = ‑0.25, as fit by forward modeling the spatial distribution of mono-[M/H] populations. The prominence of the bar decreases dramatically with [M/H], making it barely discernible at [M/H] ≲ ‑1.5. Yet, even for metal-rich populations, the bar has little impact on the azimuthally averaged profile of the mono-abundance components. Including ages, we find that the scale length is a greater function of age than of metallicity, with younger populations far more centrally concentrated. Only at old ages does the scale length change, specifically decrease, with increasing metallicity. These findings provide quantitative support for a scenario in which the LMC built its stellar structure effectively outside-in.

Keywords: Dwarf irregular galaxies, Galaxy structure, Metallicity, Large Magellanic Cloud
Potential Technosignature from Anomalously Low Deuterium/Hydrogen in Planetary Water Depleted by Nuclear Fusion Technology. Deuterium–deuterium (DD) fusion is viewed as an ideal energy source for humanity in the far future, given a vast seawater supply of D. Here, we consider long-lived, extraterrestrial, technological societies that develop DD fusion. If such a society persisted over geologic timescales, oceanic deuterium would diminish. For an ocean mass and initial deuterium/hydrogen (D/H) ratio that were Earth-like, fusion power use of only ∼10 times that projected for humankind next century would deplete the D/H ratio in ∼(a few) ×108 yr to values below that of the local interstellar medium (ISM). Ocean masses of a few percent of Earth's would reach an anomalously low D/H in ∼106–107 yr. The timescale shortens with greater energy consumption, smaller oceans, or lower initial D/H. Here, we suggest that anomalous D/H in planetary water below local ISM values of ∼16 × 10‑6 (set by Big Bang nucleosynthesis plus deuterium loss onto dust or small admixtures of deuterium-poor stellar material) may be a technosignature. Unlike SETI using radio signals, anomalous D/H would persist for eons, even if civilizations perished or relocated. We discuss the wavelengths of strong absorption features for detecting D/H anomalies in atmospheric water vapor. These are vibrational O–D stretching at 3.7 μm in transmission spectroscopy of Earth-like worlds, ∼1.5 μm (in the wings of the 1.4 μm water band) in the shorter near-infrared for direct imaging by the Habitable Worlds Observatory, and ∼7.5-8 μm (in the wings of the broad 6.3 μm bending vibration of water) for concepts like the Large Interferometer for Exoplanets.

Keywords: Nuclear fusion, Technosignatures, Transmission spectroscopy, Isotope shifts, Astrobiology, Search for extraterrestrial intelligence