Sazuna/UAT_keywords huggingface dataset:
Higher-order Mean-motion Resonances Can Form in Type I Disk Migration. Type I disk migration can form a chain of planets engaged in first-order mean-motion resonances (MMRs) parked at the disk inner edge. However, while second- or even third-order resonances were deemed unlikely due to their weaker strength, they have been observed in some planetary systems, e.g., TOI-178 bc (5:3), TOI-1136 ef (7:5), and TRAPPIST-1 bcd (8:5─5:3). We performed &gt;6000 Type I simulations of multiplanet systems that mimic the observed Kepler sample in terms of stellar mass, planet size, multiplicity, and intra-system uniformity over a parameter space encompassing transitional and truncated disks. We found that Type I migration coupled with a disk inner edge can indeed produce second- and third-order resonances (in a state of libration) in ∼10% and 2% of resonant-chain systems, respectively. Moreover, the relative occurrence of first- and second-order MMRs in our simulations is consistent with observations (e.g., 3:2 is more common than 2:1; while second-order 5:3 is more common than 7:5). The formation of higher-order MMRs favors slower disk migration and a smaller outer planet mass. Higher-order resonances do not have to form with the help of a Laplace-like three-body resonance, as was proposed for TRAPPIST-1. Instead, the formation of higher-order resonances is assisted by breaking a preexisting first-order resonance, which generates small but nonzero initial eccentricities (e ≍ 10−3 to 10−2). We predict that (1) librating higher-order resonances have higher equilibrium e (∼0.1), (2) are more likely found as an isolated pair in an otherwise first-order chain, and (3) more likely emerge in the inner pairs of a chain.

Keywords: Exoplanet dynamics, Orbits, Celestial mechanics, Exoplanet formation, Modified Newtonian dynamics, N-body simulations
Radio and Optical Flares on the dMe Flare Star EV Lac. We present the results of a coordinated campaign to observe radio and optical stellar flares from the nearby M dwarf flare star EV Lac. From a total of 27 hr of radio and 29 hr of optical observations, we examine the correspondence of the action of accelerated electrons of different energies in two distinct regions of the stellar atmosphere. We find that out of nine optical flares with suitable radio coverage, only four have plausible evidence for a radio response. Optical photometric properties cannot predict which flares will have a radio response. From flares with time-resolved optical spectroscopy available, optical-only flares have similar implied electron distributions, while those with radio responses better correlate with higher low-energy cutoffs. The optical flares with a radio response all exhibit a delay between the optical and radio peaks of ≍1 and 7 minutes, with the optical flare peaking earlier in all cases. This likely indicates that multiple loops are involved in the event, and/or the different impacts on electrons trapped in a magnetic loop (producing radio emission), versus those directly precipitating from the loop (producing the optical flare). We also remark on the radio spectral index behavior at early times for the largest radio flare observed in this study, which we interpret as evidence for increased opacity from a chromospheric evaporation front.

Keywords: Stellar flares, Optical flares
Long-term Multiwavelength Observations of RX J0440.9+4431: Unraveling the Mysteries of the Missing X-Ray Outburst and the Unique Giant Outburst. RX J0440.9+4431 is a Be/X-ray binary. Since its discovery, the Hα equivalent width (EW) of this source has exhibited three peaks, which correspond to different X-ray activities: three type I X-ray outbursts, no outburst, and a combined type I + type II outburst. In this work, we present photometric and spectroscopic observations spanning 2008─2023 and 2011─2023, respectively, covering the three peaks of Hα EW. Combined with related multiwavelength public data, we investigate the long-term evolution of RX J0440.9+4431. We propose that the longer disk growth time prior to 2010 led to a higher-density disk and triggered three type I outbursts. In contrast, the more rapid disk growth preceding 2018 resulted in lower disk density, and material accreted during the neutron star's periastron passage was insufficient to trigger outburst. Later, the disk began to dissipate but ended with a substantial size and residual material. This prior density accumulation, combined with renewed growth, yielded a much higher-density disk at maximum extent during the subsequent phase, ultimately triggering the unique type II outburst.

Keywords: Neutron stars, Be stars, High mass x-ray binary stars, Circumstellar disks
Tracing Gas Kinematics and Interactions between H II Regions and Molecular Clouds Using VLA Observations of Recombination Lines and Hydroxyl. Observational studies of H II region─molecular cloud interactions constrain models of feedback and quantify its impact on the surrounding environment. A recent hypothesis proposes that a characteristic spectral signature in ground state hyperfine lines of hydroxyl (OH)—the OH flip—may trace gas that is dynamically interacting with an expanding H II region, offering a new means of probing such interactions. We explore this hypothesis using dedicated Jansky Very Large Array observations of three Galactic H II regions, G049.205−0.343, G034.256+0.145, and G024.471+0.492, in 1─2 GHz continuum emission, all four 18 cm ground-state OH lines, and multiple hydrogen radio recombination lines. A Gaussian decomposition of the molecular gas data reveals complex OH emission and absorption across our targets. We detect the OH flip toward two of our sources, G049.205−0.343 and G034.256+0.145, finding agreement between key predictions of the flip hypothesis and the observed multiwavelength spectra, kinematics, and morphology. Specifically, we demonstrate a strong spatial and kinematic association between the OH flip and the ionized gas of the H II regions—the first time this has been demonstrated for resolved sources—and evidence from 13CO(1─0) data that the expected OH component originates from the nondisturbed gas of the parent cloud. While we detect no flip in G024.471+0.492, we do find evidence of interacting molecular gas traced by OH, providing further support for OH's ability to trace H II region─molecular cloud interactions.

Keywords: Radio spectroscopy, Interstellar molecules, Stellar feedback, H II regions, Interstellar medium, Radio astronomy, Hydroxyl sources
The AstroSat UV Deep Field South. V. Constraints on the Average Escape of Ionizing Photons in the Cosmic Dusk. We investigate the escape of ionizing (Lyman-continuum (LyC)) photons from 49 star-forming galaxies at redshifts of ∼1─1.5, using far-UV imaging from the Ultra-Violet Imaging Telescope on board AstroSat. The sample spans a wide range of stellar masses ( 8.3≲log10(M*/M⊙)≲10.1 ) and UV luminosities (−20.6 ≲ MUV ≲ −17.5). LyC emission is undetected in most galaxies (42/49), and stacking these galaxies only yields an upper limit on the observed LyC-to-nonionizing UV flux density ratio ( (Fλ,LyC/Fλ,UV)obs&lt;0.12 ). This corresponds to an absolute escape fraction upper limit of a few percent (&lt;fesc,abs&gt; &lt;0.03), under a range of stellar population assumptions. Including all galaxies (with seven LyC-leaker candidates) produces a marginal 2.4σ detection, suggesting that the average LyC signal is driven by a small number of sources. To identify the conditions favorable for LyC escape, we perform stacking analyses in bins of stellar mass, UV slope, compactness, inclination, and star formation rate surface density. A stacked LyC signal is detected at a significance of ∼3σ from a subset of galaxies that are characterized as being compact, have high star formation rate surface densities, and blue UV continuum slopes, despite each of these being individually undetected in LyC. This provides the first systematic evidence at z ∼ 1─1.5 linking these properties to LyC escape, consistent with trends observed in the lower redshift universe. Additionally, LyC leakage appears more efficient in low-mass galaxies ( log10(M*/M⊙)&lt;9.5 ), with their average absolute escape fraction ranging from &lt;fesc,abs&gt; ∼ 0.1─0.2 depending on stellar population assumptions. These results support the scenario that compact, low-mass starbursts were key contributors to the ionizing photon budget during cosmic reionization.

Keywords: Ultraviolet astronomy, Reionization
Dust Evolution in Simulated Multiphase Galactic Outflows. We present the first large-scale, high-resolution simulations of dusty, star formation feedback-driven galactic outflows. Using the Cholla hydrodynamics code, we investigate dust sputtering in these environments for grains ranging in size from 1 to 0.001 μm. We compare results for two feedback models: one representative of low-redshift nuclear starburst galaxies and one similar to high-redshift main-sequence galaxies. In general, our simulations show that multiphase outflows are capable of safely transporting a vast majority of their dust to large distances (∼10 kpc) from the disk. This work also shows that environmental shielding in cool gas clouds boosts dust survival rates significantly. The evolutionary path of dust depends strongly on grain size. Large grains (a ≥ 0.1 μm) can be transported efficiently in all phases. Smaller grains, however, experience significant destruction in the hotter phases. In particular, 0.001 μm grains are quickly sputtered in all but the coolest gas, resulting in these grains strongly tracing the cool phase in outflows. These results may also indicate the importance of in situ formation mechanisms, such as shattering, for the small dust grains and polycyclic aromatic hydrocarbons observed in emission throughout outflows in nearby galaxies. Surprisingly, we find that the hot phase dominates the transport of dust that survives to populate the circumgalactic medium.

Keywords: Galactic winds, Dust destruction, Circumgalactic medium
Dance to Demise—How Massive Stars May Form Dense Circumstellar Shells before Explosion. We investigate the evolution of red supergiant (RSG) progenitors of core-collapse supernovae (SNe) with initial masses between 12 and 20 M⊙, focusing on the effects of enhanced mass loss due to pulsation-driven instabilities in their envelopes and subsequent dynamical ejections during advanced stages of nuclear burning. Using time-dependent mass loss from detailed Modules for Experiments in Stellar Astrophysics (MESA) stellar evolution models, including a parameterized prescription for pulsation-driven superwinds and time-averaged mass-loss rates attributed to resulting shock-induced ejections, we construct the circumstellar medium (CSM) before the SN explosion. We calculate resulting CSM density profiles and column densities considering the acceleration of the stellar wind. Our models produce episodes of enhanced mass loss (∼10−4─10−2 M⊙ yr−1) in the last centuries—decades before explosion forming dense CSM (≳10−15 g cm−3 at distances ≲1015 cm)—consistent with those inferred from multiwavelength observations of Type II SNe such as SN 2023ixf, SN 2020ywx, SN 2017hcc, SN 2005ip, and SN 1998S. The formation of such dense circumstellar shells, within the explored range of our single star RSG models, provides a natural explanation for observed flash-ionization signatures, X-ray and radio emission, and has important implications for dust formation around Type II SNe.

Keywords: Late stellar evolution, Red supergiant stars, Type II supernovae, Circumstellar matter, Stellar winds
Resolving the Dusty Star-forming Galaxy GN20 at z = 4.055 with NOEMA and JWST: A Similar Distribution of Stars, Gas, and Dust Despite Distinct Apparent Profiles. We present high-resolution (0 .″ 13─0 .″ 23) NOEMA observations of the dust continuum emission at 1.1 mm (rest frame 220 μm) and JWST/NIRCam and MIRI imaging of the z = 4.055 starburst galaxy GN20. The sensitive NOEMA imaging at 1.6 kpc resolution reveals extended dust emission, ≍14 kpc in diameter (re ≍ 2.5 kpc, b/a = 0.5), which is centrally asymmetric and clumpy. The dust emission is as extended as the stellar emission and molecular gas traced by 12CO(2─1), with a common center, and is brightest in the strongly obscured nuclear part of the galaxy. Approximately one-third of the total dust emission emerges from the nucleus and the most prominent clump to the south, with (only) 60% from the central 3.5 × 1.5 kpc (0 .″ 5─0 .″ 2), implying that the starburst is very extended. The combined JWST and NOEMA morphology suggests GN20 experienced a recent interaction or merger, likely invigorating the starburst. The radial surface brightness profiles of the molecular gas and near-IR stellar emission are similar, while, in contrast, the dust emission appears significantly more concentrated. Through self-consistent radiative-transfer modeling of the integrated and resolved 12CO and dust emission, we derive  Mmol=2.9−0.3+0.4×1011 f M⊙, with  αCO=2.8−0.3+0.5 . We find the extended dust implies a lower global dust optical depth than previously reported but a high dust mass of  Mdust=5.7−0.6+0.8×109  M⊙ and gas-to-dust ratio of ≍50. Furthermore, we show that the distinct apparent radial profiles of the gas and dust can be explained purely by radiative-transfer effects (differences in the radial optical depths and temperatures), and that the observations are consistent with the gas and dust masses being similarly distributed throughout the starburst. The latter highlights the importance of accounting for radiative-transfer effects when comparing molecular gas and dust distributions from different tracers.

Keywords: Millimeter astronomy, Galaxy structure, James Webb Space Telescope, Dust continuum emission, High-redshift galaxies
The Route to Unveil the Cosmic Genealogy of Supermassive Black Hole Binaries Using Nanohertz Gravitational Waves and Galaxy Surveys. The nanohertz stochastic gravitational wave background (SGWB), generated by unresolved supermassive black hole binaries (SMBHBs), provides a unique probe of their population and its cosmic evolution. In this work, we explore the potential of uncovering the SMBHB population and its redshift dependence by combining the SGWB signal and its anisotropies with galaxy distribution through cross-correlation analyses. Using a Fisher analysis technique, we show that the SGWB power spectrum alone can not provide any information on the evolutionary history of SMBHBs, whereas the inclusion of the angular power spectrum of the SGWB and its cross-correlation with the galaxy distribution substantially improves constraints on the redshift evolution parameters. Assuming pulsar timing array configurations achievable in the Square Kilometre Array era, we find that the combined use of isotropic and anisotropic SGWB signals, together with galaxy surveys, can provide valuable measurements of the redshift evolution of the SMBH─galaxy connection and the frequency distribution of SMBHBs. These results highlight the potential of joint gravitational wave─galaxy studies to address the long-standing open question of SMBH growth and evolution across cosmic time.

Keywords: Cosmology, Supermassive black holes, Gravitational waves
Rapid γ-Ray Variability in the Lensed Quasar PKS 1830−211 Observed by Fermi-LAT. We report a detailed analysis of the γ-ray light curve from the source PKS 1830─211, where five γ-ray flares with peak fluxes larger than 10−5 ph cm−2 s−1 were obtained. The observed shortest variability timescale of 0.83 ± 0.33 hr suggests a very compact emission region of R ≤ 1015 cm and a Doppler factor of ∼40, implying that the observed emission is most likely produced in the subparsec-scale jet. The majority of short-timescale flares show an asymmetric temporal profile, implying that the flares may be attributed to the fast injection of accelerated particles or escape from the emission region. Moreover, the γ-ray spectra show an obvious spectral break with cutoff energies between 3.83 and 5.57 GeV, which may be caused by an intrinsic break in the energy distribution of radiating particles. The obtained γ-ray power spectral densities imply that the seed photons could originate from the dusty torus with a total photon luminosity Lph ∼ 1.2 × 1050 erg s−1 for the magnetic island in comoving frame. According to the intermittency of turbulent cascade, we get the scale of the reconnection layers of ∼0.2 × 1017 cm and the survival time of a sheet of τcs ∼ 2.4 × 104 s, which is less than the shock acceleration timescale of tacc ≍ 6.0 × 104 s. These results hint that the ultrafast γ-ray variability from PKS 1830−211 may be due to the magnetic reconnection mechanism.

Keywords: Blazars, Relativistic jets, Active galactic nuclei, Gamma-rays
The Radio Afterglow of the Ultralong GRB 220627A. We present the discovery of the radio afterglow of the most distant ultralong gamma-ray burst (GRB) detected to date, GRB 220627A at redshift z = 3.084. Its prompt gamma-ray light curve shows a double-pulse profile, with the pulses separated by a period of quiescence lasting ∼15 minutes, leading to early speculation it could be a strongly gravitationally lensed GRB. However, our analysis of the Fermi Gamma-ray Burst Monitor spectra taken during the time intervals of both pulses show clear differences in their spectral energy distributions, disfavouring the lensing scenario. We observed the radio afterglow from 7 to 456 days postburst: an initial, steep decay (Fν ∝ t−2) is followed by a shallower decline (Fν ∝ t−1/2) after ∼20 days. There are three scenarios that could explain these radio properties: (i) energy injection from an additional, slower ejecta component catching up to the external shock; (ii) a stratified density profile going as n ∝ r−8/3; or alternatively, (iii) the presence of a slow, wide ejecta component in addition to a fast, narrow ejecta component. We also conducted an independent test of the lensing hypothesis via very long baseline interferometry (VLBI) observations at ∼12 days postburst by searching, for the first time, for multiple images of the candidate lensed GRB afterglow. Our experiment highlighted the growing need for developments in real-time correlation capabilities for time-critical VLBI experiments, particularly as we advance towards the SKA and ngVLA era of radio astronomy.

Keywords: Strong gravitational lensing, Gamma-ray bursts, Time domain astronomy, Very long baseline interferometry
Radio Follow-up Observations of a Weak-line Quasar Exhibiting Remarkable X-Ray Variability. SDSS J1539+3954 (z ≍ 1.935), a radio-quiet weak-line quasar (WLQ), exhibited exceptional X-ray variability in 2019─2020, with its X-ray flux increasing by over 20 times from 2013 to 2019 and subsequently dropping by at least a factor of 9 in 2020. Motivated by the empirical correlations between X-ray and radio emission in the cores of active galactic nuclei (AGNs), we carried out a follow-up radio study in the 0.3─10 GHz range using the Giant Metrewave Radio Telescope (GMRT; 2020, 2022, 2024) and Very Large Array (VLA; 2022), and analyzed archival Very Large Array Sky Survey (VLASS) 3 GHz data (2017─2023) to investigate the source's radio properties and potential connection with the X-ray behavior. Our observations reveal a compact radio source with a spectral index of −0.65 ± 0.15 in the frequency range 0.3─1.4 GHz and −1.09 ± 0.16 in 3─10 GHz. While the source was undetected in VLA-FIRST (1994) and VLASS epochs, the GMRT and VLA observations show no statistically significant variability over the monitored period. The absence of detectable changes in the radio flux, despite strong X-ray variability, suggests no direct connection between the X-ray variability and the radio emission, consistent with the thick-disk-plus-outflow (TDO) model for WLQs. However, the sensitivity limit of the surveys prevents us from drawing definitive conclusions regarding variability on longer timescales between the VLA-FIRST and GMRT epochs. We further explore possible mechanisms driving the radio emission from this source. Our analysis rules out small-scale jets and coronal emission as the primary drivers of the radio emission, suggesting that extended emission from AGN winds and star formation is the more plausible mechanism.

Keywords: Quasars, Active galaxies, Radio quiet quasars, Active galactic nuclei, Radio sources
Illuminating the Diffuse Radio Emission in Low-mass Cluster A13. Recent advances in high-sensitivity radio observations have uncovered a population of faint, ultrasteep-spectrum sources in galaxy clusters, commonly known as radio phoenixes. However, their observational classification remains poorly constrained due to the limited number of confirmed detections. This study presents a detailed multifrequency, high-sensitivity, and high-resolution analysis of diffuse radio emission in the merging galaxy cluster Abell 13 (A13). Using Giant Metrewave Radio Telescope (GMRT; 147.5 MHz), upgraded GMRT (400 MHz), ASKAP-low (887.5 MHz), and MGCLS (1284 MHz) images, we detect complex, filamentary diffuse emission with a largest linear extent of 521 kpc. This emission originates from the cluster center and extends westward, confined within the X-ray-emitting intracluster medium. Chandra X-ray data confirm that A13 is undergoing a merger, and the radio morphology reflects signatures of this ongoing dynamical activity. We observed filamentary structures extending toward east─northeast and southwest directions. The spectral index across the emission appears irregular and lacks a coherent spatial gradient. The integrated spectrum reveals a steep spectral index of −1.85 ± 0.05 and a spectral curvature of −0.93 ± 0.21. These spectral properties, along with the observed morphology and brightness distribution, are consistent with a reenergization of a fossil radio plasma driven by adiabatic compression, supporting the classification of the emission as a radio phoenix.

Keywords: Radio continuum emission, Abell clusters, Intracluster medium, Non-thermal radiation sources
Weak-lensing Approximation of Wave-optics Effects from General Symmetric Lens Profiles. Gravitational lensing of electromagnetic (EM) waves has yielded many profound discoveries across fundamental physics, astronomy, astrophysics, and cosmology. Similar to EM waves, gravitational waves (GWs) can also be lensed. When their wavelength is comparable to the characteristic scale of the lens, wave-optics (WO) effects manifest as frequency-dependent modulations in the GW waveform. These WO features encode valuable information about the lensing system but are challenging to model, especially in the weak-lensing regime, which has a larger optical depth than the strong-lensing regime. We present a novel and efficient framework to accurately approximate WO effects induced by general symmetric lens profiles. Our method is validated against numerical calculations and recovers the expected asymptotic behavior in both high- and low-frequency limits. Accurate and efficient modeling of WO effects in the weak-lensing regime will enable improved lens reconstruction and delensing of standard sirens and provide a unique probe to the properties of low-mass halos with minimal baryonic content, offering new insights into the nature of dark matter.

Keywords: Gravitational wave astronomy, Gravitational lensing, Weak gravitational lensing