Sazuna/UAT_keywords huggingface dataset:
Ionized Gas Components in Low Surface Brightness Galaxy AGC 111629. We present integral field spectroscopy of ionized gas components in AGC 111629, an edge-on low surface brightness galaxy with a stellar mass of 5.7 × 108 M⊙. AGC 111629 displays an irregular Hα morphology and an arch-like structure in the extraplanar region, which is absent in continuous stellar image. The irregular Hα morphology may be related to a past merger event with its satellite galaxy AGC 748815. A peanut-shaped structure at the center in the integrated [O III]λ5007 map, with a position angle that differs from that of the main stellar disk. This structure exhibits a higher [O III]λ5007/Hβ flux ratio, a larger equivalent width of [O III]λ5007, and a lower Hα/Hβ flux radio (&lt;2.86). Some spaxels associated with the peanut-shaped structure fall within the composite region of the Baldwin─Phillips─Terlevich diagram based on [N II]λ6583. These features may be associated with the central active galactic nucleus (AGN). Additionally, a subpeak in the southern disk is clearly visible in the [O III]λ5007 map. An extended region (∼2 kpc) with an extremely low value of Hα/Hβ flux ratio is observed near this subpeak. We interpret the subpeak as a superbubble likely driven by supernova explosions in the southern disk. We derive the gas-phase metallicity, 12+log(O/H), using the [N II]λ6583/Hα diagnostic and find that AGC 111629 exhibits low central metallicity. This may result from feedback associated with AGN activity and supernova explosions.

Keywords: AGN host galaxies, Supernova remnants, Galaxy mergers, Metallicity, Low surface brightness galaxies
Characterizing Temperatures of Flares on the M Dwarf Wolf 359 from Simultaneous Multiband Optical Observations. We present a flare temperature study of the highly active M dwarf Wolf 359 using simultaneous multiband (u, g, r, i, and z) photometric observations from the Lulin 1 m and 41 cm telescopes. Twelve flares were detected over five nights, with significant brightness increases in the u, g, and r bands; only three were seen in i, and none in z. From broadband spectral energy distribution fitting and g/r color ratio, we derive an average flare temperature of 5500 ± 1600 K, significantly cooler than the canonical 10,000 K. We obtained a power-law relation between FWHM flare temperature and energy in the solar-class flare regime and extrapolated it to higher energies, superflare regime. This power-law is consistent with the trends reported for M dwarf superflares in previous studies, suggesting a common temperature─energy scaling across several orders of magnitude. However, the scatter in the superflare regime increases, indicating that such energetic events may involve more complex physical mechanisms and limiting the applicability of simple blackbody models at the high-energy flares. Using our FWHM flare temperature─TRIPOL g energy relation and the reported flare energy frequency distribution of Wolf 359, we evaluated the potential flare contribution to photosynthetically active radiation (PAR) in the habitable zone. We find that typical solar-class giant flares (Efl,bol ∼ 9 × 1031 erg, Tfl,fwhm ∼ 6800 K) are not frequent enough to sustain Earth-like net primary productivity. Even under the extreme superflare condition (∼1036 erg, ∼16,500 K), flare activity remains far from meeting the PAR threshold.

Keywords: M dwarf stars, Red dwarf flare stars, Flare stars, Optical flares, Ground telescopes
A Comprehensive Reanalysis of K2-18 b's JWST NIRISS+NIRSpec Transmission Spectrum. Sub-Neptunes are the most common type of planet in our galaxy. Interior structure models suggest that the coldest sub-Neptunes could host liquid water oceans underneath their hydrogen envelopes—sometimes called "hycean" planets. JWST transmission spectra of the ∼250 K sub-Neptune K2-18 b were recently used to report detections of CH4 and CO2, alongside weaker evidence of (CH3)2S (dimethyl sulfide, or DMS). Atmospheric CO2 was interpreted as evidence for a liquid water ocean, while DMS was highlighted as a potential biomarker. However, these notable claims were derived using a single data reduction and retrieval modeling framework, which did not allow for standard robustness tests. Here, we present a comprehensive reanalysis of K2-18 b's JWST NIRISS SOSS and NIRSpec G395H transmission spectra, including the first analysis of the second-order NIRISS SOSS data. We incorporate multiple well-tested data reduction pipelines and retrieval codes, spanning 60 different data treatments and over 250 atmospheric retrievals. We confirm the detection of CH4 (≍4σ), with a volume mixing ratio range  −2.14≤log10CH4≤−0.53 , but we find no statistically significant or reliable evidence for CO2 or DMS. Finally, we assess the retrieved atmospheric composition using photochemical-climate and interior models, demonstrating that our revised composition of K2-18 b can be explained by an oxygen-poor mini-Neptune without requiring a liquid water surface or life.

Keywords: Exoplanet atmospheric composition , Ocean planets, Exoplanets, Exoplanet surfaces, Extrasolar gaseous planets, Exoplanet structure, Mini Neptunes, Habitable planets, Exoplanet atmospheres
Identifying Close-in Jupiters that Arrived via Disk Migration: Evidence of Primordial Alignment, Preference of Nearby Companions and Hint of Runaway Migration. Two leading hypotheses for hot Jupiter migration are disk migration and high-eccentricity migration (HEM). Stellar obliquity is commonly used to distinguish them, as high obliquity often accompanies HEM. However, low obliquity does not guarantee disk migration, due to possible spin─orbit realignment or coplanar HEM. Seeking a proxy for disk migration, we investigate the idea that when the circularization timescale of a planet on circular orbit is longer than its age (τcir &gt; τage), HEM would not have had sufficient time to complete, favoring disk migration. We empirically calibrate the reduced planetary tidal quality factor to be  Qp=4.9−2.5+3.5×105  using the eccentricity distribution of 500+ Jovian mass (0.2MJ &lt; Mp &lt; 13MJ) planets with measured masses and radii, a value consistent with solar system Jupiter. We then calculate τcir and identify dozens of disk migration candidates (τcir &gt; τage, e &lt; 0.1). These planets show three notable trends. We first find a clear cutoff of obliquity at τcir ∼ τage, suggesting the primordial alignment of protoplanetary disks. Second, we find that among hot Jupiters (a &lt; 0.1 au), nearby companions are preferentially found around disk migration candidates, suggesting that either HEM dominates hot Jupiter formation, or disk migration also disrupts nearby companions at short separations. Finally, we find a possible dearth of disk migration candidates around mass ratio  logq∼−3.2 , consistent with a similar dip suggested at longer orbits from microlensing. The lack of planets across different orbital distance, if true, could be interpreted as a hint of runaway migration.

Keywords: Exoplanet migration, Hot Jupiters, Orbital evolution, Exoplanet tides, Tidal interaction, Extrasolar gaseous giant planets, Eccentricity
MEGA Mass Assembly with JWST: The MIRI EGS Galaxy and Active Galactic Nucleus Survey. We present the Mid-Infrared Instrument (MIRI) Extended Groth Strip (EGS) Galaxy and Active Galactic Nucleus (MEGA) survey, a four-band MIRI survey with 25 pointings in the EGS extragalactic field. Three pointings utilized only the three reddest bands (F1000W, F1500W, and F2100W), while the remainder also included a blue filter (F770W). MEGA builds upon the existing observations in the EGS field by providing MIRI imaging for 68.9% of CEERS NIRCam imaging, filling a crucial gap in order to understand galaxy evolution by observing the obscured Universe. Here, we present the technical design, data reduction, photometric catalog creation for our first data release, and science drivers of the MEGA survey. Our data reduction starts with the standard James Webb Space Telescope calibration pipeline but adds additional warm pixel masking and custom background subtraction steps to improve the quality of the final science image. We estimate the image depth of the reduced mosaics and present new galaxy number counts in four MIRI bands.

Keywords: Infrared photometry, Infrared sources, Astronomy data reduction
Revised Mass and Orbit of ∊ Eridani b: A 1 M<SUB>Jup</SUB> Planet on a Near-circular Orbit. The mature Jovian planet ∊ Eridani b (∊ Eri b) orbits one of the closest Sun-like stars at a moderate separation of 3.5 au, presenting one of the best opportunities to image a true analog to a solar system planet. We perform a thorough joint reanalysis and cross-validation of all available archival radial velocity (RV) and astrometry data, combining data from eight RV instruments and four astrometric sources (Hipparcos, the Hubble Space Telescope's Fine Guidance Sensor, Gaia Data Release 2, and Gaia Data Release 3). We incorporate methodological advances that impact our findings, including a principled treatment of correlation between Gaia DR2 and DR3 velocity. We revise the planet's mass upward to 1.00 ± 0.10 MJup and find that its orbit is nearly circular and likely to be to coplanar with the outer debris disk. We further present one of the first models of an exoplanet orbit exclusively from absolute astrometry and independently confirm the planet's orbital period. We make specific predictions for the planet's location at key imaging epochs from past and future observing campaigns. We discuss and resolve tensions between previous works regarding the eccentricity, inclination, and mass. Our results further support that ∊ Eri b is one of the closest analogs to a solar system planet yet detected around a nearby star.

Keywords: Radial velocity, Extrasolar gaseous planets, Astrometry, Exoplanets
The Importance of Standardizing Spectra in the Era of Large Spectroscopic Surveys: A Case Study of M Dwarfs in SDSS-V. The Fifth Sloan Digital Sky Survey (SDSS-V) will obtain hundreds of thousands of medium-resolution, optical spectra of M dwarfs with the BOSS instrument. M dwarfs have complex atmospheres, and their spectra contain many wide and densely overlapping molecular features, so determining accurate stellar parameters by fitting models has been difficult. To circumvent this, other surveys have employed machine learning methods to transfer measurements of stellar parameters from high-resolution spectra to their medium-resolution counterparts. These methods provide large catalogs of stellar parameters but, if not addressed properly, are plagued by biases which are, in part, due to the normalization of the spectra. Typical spectral normalization removes the continuum but preserves the relative depths of the absorption features, but optical M dwarf spectra are almost entirely made up of molecular absorption, which makes this difficult. Here, we develop a standardization method that instead defines a pseudocontinuum. We use the spectrum's alpha shape to find the points which lie between the absorption features and apply local polynomial regression to find this pseudocontinuum. To tune the hyperparameters of this method, we create BOSS-like spectra from BT-NextGen models to replicate instrumental, signal-to-noise ratio, and reddening effects. We find that in both this generated set and a validation set of SDSS-V data, our method performs better than alternative standardizations by producing spectra that are both more uniform for M dwarfs with similar stellar parameters and more easily distinguished compared to M dwarfs of differing parameters. These results from our method will be crucial for better determining stellar parameters of M dwarfs using generative models.

Keywords: Surveys, M dwarf stars, Spectroscopy
An Independent Search for Small Long-period Planets in Kepler Data. I. Detection Pipeline. The unprecedented photometric precision of the Kepler mission allows searches for Earth-like planets. However, it remains difficult to distinguish these low signal-to-noise-ratio planets from the false alarms originating from correlated and non-Gaussian noise. It reduces the resulting planetary catalog reliability and makes it hard to measure the occurrence rate of small long-period planets. We aim to obtain a more reliable catalog of small long-period planet candidates from Kepler data and use it to improve their occurrence rate estimates. This work develops an independent search pipeline for small (Kepler multiple-event statistic (MES) ≲ 12) long-period (50─500 days) planets. We design and implement a detection statistic that takes into account noise non-Gaussianity and physical priors. For every threshold-crossing event, we run permutation and injection procedures to calculate the probability of it being caused by a real planet. The provided detection statistic has a tailless background distribution with a rate of ∼1 false alarm per search for MES ∼ 7.8. We demonstrate an increase in detection efficiency for MESs of 7.5─9 and &gt;4 transits due to the background distribution control. The pipeline was tested and found to be able to detect most of the faint confirmed Kepler planets. The pipeline was applied to the entirety of Kepler data and detected ∼50 candidate events with a high probability of originating from real planets, which will be presented in our future work.

Keywords: Exoplanets, Astronomy data analysis, Exoplanet detection methods, Transit photometry, Time series analysis
Asteroseismology of the Red Giant Companions to Gaia BH2 and BH3. The stellar companions in the binary black hole systems Gaia BH2 and BH3, both of which are α-enhanced red giant branch stars, are expected to show normal modes with the characteristic signature of convectively driven solar-like oscillations. We investigate this using photometry from the TESS mission and find such a signal for Gaia BH2. For Gaia BH2, we measure a power excess frequency of  νmax=60.15±0.57  μHz and a large separation of ∆ν = 5.99 ± 0.03 μHz, yielding a mass of  1.19−0.08+0.08  M⊙, which is in agreement with spectroscopically derived parameters. Seismic modeling favors an age for the red giant of  5.03−3.05+2.58  Gyr, strongly suggesting that it is a young, α-enriched giant star, which are thought to arise from a binary accretion or merger scenario. Ground-based photometry of Gaia BH2 spanning 8 yr indicates a photometric period of 398 ± 5 days, which we tentatively attribute to rotation. If this rotation is physical, it cannot be explained solely by evolutionary spin-down or magnetic braking, and implies that the red giant underwent some tidal forcing mechanism. Suggestively, this period is close to the pseudosynchronous spin period of Pspin = 428 ± 1 days derived from the binary orbit. For Gaia BH3, we are unable to identify an asteroseismic signal in the TESS data despite predicting that the amplitude of the signal should lie well above the measured noise level. We discuss a number of scenarios for why this signal may not be visible.

Keywords: Asteroseismology, Black holes, Red giant stars
A New Investigation of the Molecular Environment of Supernova Remnant G40.5─0.5. Since the physical association between supernova remnant (SNR) G40.5−0.5 and the nearby bright gamma-ray source MGRO J1908+06 is yet unclear, it remains valuable to further investigate the remnant's molecular environment and establish its reliable distance despite previous studies. We perform a new inspection of the CO emission in the region covering G40.5−0.5 to search for evidence of interaction between the remnant and environmental molecular clouds (MCs). The SNR, which appears to blow out toward the southeast in radio, is found to be largely embedded within a molecular gas cavity at a local-standard-of-rest velocity range of ∼+33─+41 km s−1 and bounded on the northern side by dense gas. In this velocity range, the MCs show a blueshifted line broadening in the northeast and southwest of the remnant. A high 12CO J = 3─2/J = 1─0 line ratio is also found on the northeastern edge of the remnant. Therefore, we argue that the SNR interacts with the MCs at VLSR ∼ +33 to +41 km s−1, rather than the previously suggested velocity ∼+55 km s−1. The H I self-absorption features also support this argument. The systemic velocity of the MCs places the remnant at a kinematic distance of ∼2.3 kpc. With this distance, we have derived the fundamental physical parameters of the associated molecular gas, including the column density and volume density. The mass of the progenitor star of the SNR is inferred to be ≳15 M⊙. The remnant is considered to be in the radiative phase, with an age no larger than ∼1.9 × 104 yr.

Keywords: Supernova remnants, Shocks, Molecular clouds, Interstellar medium
A Semianalytical Method of Frequency-average Smearing for Radio Interferometers based on Point Source. Next-generation radio interferometers, with their enhanced spatial, temporal, and high-frequency resolution, will pose considerable challenges to data processing and storage. Frequency averaging reduces the volume of data, but would cause smearing of the bandwidth. The examination of bandwidth smearing is essential in the processing of radio interferometer data to achieve scientific objectives. Existing analysis methods can quantify parameters such as peak intensity loss in restored images under ideal assumptions. However, determining the shape of the source smearing in dirty images requires using complex observational simulation methods, which limits comprehensive studies of bandwidth smearing from frequency averaging and its optimal application. In this paper, we introduce a semianalytical method (SAM) and validate its accuracy through the simulation method. The SAM efficiently and precisely evaluates the impact of the smearing effect from frequency averaging for various telescope pointing positions, offering a plausible "distorted beam" representation of the non-phase-centered beam shape of point sources in the dirty image. Based on this beam shape, the specific shape of smearing after frequency averaging can be accurately and comprehensively described. This not only enables the determination of the extent of smearing, prediction of accuracy loss, and formulation of effective observation and data processing strategies prior to data processing, but also facilitates the development of more advanced frequency averaging methods.

Keywords: Radio telescopes, Radio interferometers
Exploring the Mass─Metallicity Relationships with the DESI BGS and ELG Samples. The mass─metallicity relation (MZR) serves as a cornerstone for understanding the chemical evolution of galaxies by correlating the stellar mass of galaxies with their gas-phase metallicity. Using data from the Bright Galaxy Survey (BGS) and emission-line galaxy (ELG) samples from the early data release of the Dark Energy Spectroscopic Instrument, we examine the MZR at z ∼ 0.18 and z ∼ 0.86, respectively. The analysis includes 30,943 star-forming galaxies from BGS and 22,784 from ELG. Both samples exhibit typical MZR trends, but with a significantly steeper slope in the ELG sample. The BGS sample shows clear redshift evolution, with metallicity increasing over time at fixed stellar mass, whereas such evolution is not evident in the ELG sample, likely due to large stellar mass uncertainties. We further investigate the fundamental metallicity relation (FMR) for both populations. The inclusion of star formation rate (SFR) in the FMR framework reduces the scatter compared to the MZR in both samples, and the BGS FMR supports a nonevolving M⋆─SFR─metallicity relation. The comparison of the FMR slopes between BGS and ELG reveals that, even after accounting for the effect of SFR, the two populations still exhibit residual differences. This result indicates that the FMR only partially reconciles their metallicity scaling relations and that ELGs deviate from the nonevolving relation derived from the BGS.

Keywords: Galaxy formation, Galaxy properties
Performance Comparison of Source Finders in Imaging Quality Assessment for SKA1-LOW. The Square Kilometre Array (SKA) telescope is poised to yield massive observational data every year. The continuum imaging pipeline is a key and significant SKA data processing pipeline. An exact assessment of the continuum imaging outcomes not only serves to ascertain the overall operational integrity of the telescope but also furnishes invaluable references for subsequent data processing. In response to the urgent requirement for objective and accurate imaging quality assessment (QA) of the SKA continuum imaging pipeline, we empirically investigated the performance and availability of four source finders based on the full-scale SKA1-LOW simulation data generated by the OSKAR and the Radio Astronomy Simulation, Calibration, and Imaging Library (RASCIL2), carefully analyzing the performance of the source finder under different scenarios such as different thermal noise levels, imaging sizes, and field of view. We finally optimized the QA pipeline for SKA1-LOW according to empirical results, resulting in a discernible enhancement in both the performance and the accuracy of the pipeline.

Keywords: Aperture synthesis
LAMOST Medium-resolution Spectroscopic Survey of the Rosette Nebula. We report multifiber, medium-resolution spectroscopy of the Rosette Nebula with full spatial coverages, and present a table of the nebular parameters based on the spatially resolved measurements of emission lines. These new observations were conducted through the Medium-Resolution Spectroscopic Survey of Nebulae (MRS-N) on the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST). Comprehensive analyses were performed on a total of 3854 high-quality nebular spectra; so far, the most extensive spectral data set available for this nebula that encompasses an area of 4.52 square degrees. Various physical parameters, including relative line intensities, radial velocities (RVs), and full width at half-maximums (FWHMs), were derived through measurements of the Hα, [N II] λλ6548,6584 and [S II] λλ6716,6731 emission lines detected in the LAMOST MRS-N spectra. For the first time, we found a bow-shaped feature in the spatial distribution of RVs of the Rosette Nebula. Moreover, the spatial distributions of RVs and FWHMs, as well as additional parameters such as gas temperature and turbulent velocity in the vicinity of the nebula, indicate possible interaction between Rosette and the nearby supernova remnant, Monoceros Loop. Our new observations provide indispensable measurements of the Rosette Nebula. The parameter table in particular can be used as valuable constraint on the chemo-dynamical modeling of the nebula, which will enable deeper understanding of the characteristics of this H II region.

Keywords: Gaseous nebulae, Emission nebulae, Interstellar medium, Spectroscopy, H II regions