Sazuna/UAT_keywords huggingface dataset:
Vertical Shear Instability in Thermally Stratified Protoplanetary Disks. II. Hydrodynamic Simulations and Observability. We conduct 3D hydrodynamic simulations to investigate the nonlinear outcomes and observability of vertical shear instability (VSI) in protoplanetary disks. Our models include both vertically isothermal and thermally stratified disks, with the latter representing realistic conditions featuring a hotter atmosphere above the midplane. We find that the VSI grows more rapidly and becomes stronger in thermally stratified disks due to enhanced shear, resulting in higher levels of turbulence. At saturation, the turbulence stress reaches αRϕ ≳ 10‑3, more than 1 order of magnitude stronger than the isothermal case. The saturated turbulence is more pronounced near the disk surfaces than at the midplane. On synthetic velocity residual maps, obtained by subtracting the Keplerian rotational velocity, perturbations driven by the VSI manifest as axisymmetric rings in isothermal disks and as ring segments in thermally stratified disks. The latter are visible at disk inclinations as high as 45° in thermally stratified disks. The amplitudes of these residual velocities range from ∼50 to ∼100 m s‑1 at a 20° inclination, with larger values corresponding to greater thermal stratification. The magnitude of the observed velocity residual increases with the optical depth of the tracer used, as optically thick lines probe the regions near the disk surfaces.

Keywords: Accretion, Hydrodynamical simulations, Hydrodynamics, Radiative transfer, Protoplanetary disks
Coordinated Velocity Shift of Multiple C IV and Si IV Broad Absorption Lines in Quasar SDSS J113048.45+225206.6. We present an analysis of the coordinated velocity shifts observed in multiple C IV and Si IV broad absorption lines (BALs) in the quasar SDSS J113048.45+225206.6. The quasar exhibits an extensive BAL system spanning a velocity range of approximately 13,000 km s‑1, which can be further delineated into five absorption systems (A1 to A5). Our analysis revealed coordinated velocity shifts in the C IV BALs of systems A1 and A2 and in the Si IV BALs of systems A2 and A3. These shifts were accompanied by coordinated variations in equivalent widths, which can be attributed to changes in the ionization state of the clouds in response to fluctuations in the ionizing continuum. By comparing the absorption line systems, we deduced that the velocity-shifted systems (A1 to A3) are located closer to the central engine, possess higher velocities, and are in a higher ionization state compared to the nonshifted systems (A4 to A5). These characteristics suggest that the outflow producing the velocity-shifted systems is situated in a more extreme environment and is more severely impacted by background radiation energy than the nonshifted systems. Furthermore, the synchronization of these velocity shifts across multiple components suggests a common underlying mechanism. Consequently, we infer that the coordinated velocity-shift signatures may indicate actual deceleration of the outflow clouds, driven by radiation pressure from the background light source.

Keywords: Quasars, Quasar absorption line spectroscopy, Broad-absorption line quasar
Contribution of Unresolved Sources to Diffuse Gamma-Ray Emission from the Galactic Plane. The diffuse gamma-ray emission from the Milky Way serves as a crucial probe for understanding the propagation and interactions of cosmic rays within our Galaxy. The Galactic diffuse gamma-ray emission between 10 TeV and 1 PeV has been recently measured by the square kilometer array (KM2A) of the Large High Altitude Air Shower Observatory (LHAASO). The flux is higher than predicted for cosmic rays interacting with the interstellar medium. In this work, we utilize a nonparametric method to derive the source count distribution using the published first LHAASO source catalog. Based on this distribution, we calculate the contribution of unresolved sources to the diffuse emission measured by KM2A. When comparing our results to the measured diffuse gamma-ray emission, we demonstrate that for the outer Galactic region, the contributions from unresolved sources and those predicted by models are roughly consistent with the observations within the uncertainties. However, for the inner Galactic region, additional components are required to account for the observed data.

Keywords: Diffuse radiation, Gamma-ray astronomy, Cosmic background radiation
The Eruptive Duality of a Filament on 2023 April 21. Here we study a filament eruption on 2023 April 21. The filament was composed of two segments, named S1 and S2. Initially, the brightening and bidirectionally plasmoid flows appeared inside S1, and then the west part of S1 (WS1) experienced rapid rising and eruption, accompanied by coronal dimming, flare ribbons, and a secondary flare ribbon. However, the east part of S1 (ES1) rose slowly and was confined. The material within ES1 drained back to its eastern footpoint, resulting in the footpoint brightening. In the later phase, the south footpoint of the stable extreme-ultraviolet (EUV) loops overlying ES1 was brightened also, which may result from the disturbance of drainage. During S1 eruption and activation, S2 remained stable. Nonlinear force-free field extrapolation shows that the footpoints of the magnetic field lines overlying WS1 are rooted on the flare ribbons, while the field lines overlying ES1, which share a negative field with other lines, correspond to the stable EUV loops. Based on potential field extrapolation, we calculate the decay index of the background fields overlying the filament. It indicates that the critical height of the torus instability of the fields overlying WS1 is lower than that overlying ES1. To interpret this filament eruption, we first put forward the eruptive duality, characterized by the eruption of the partial filament structure and the confinement of the other structure, and this duality is determined by the properties of the overlying fields.

Keywords: Solar activity, Solar flares, Solar filaments, Solar filament eruptions
Revisiting the Flaring Activity in Early 2015 of BL Lacertae Object S5 0716+714. In this work, we analyzed multiwavelength data of the BL Lac object S5 0716+714 to investigate its emission mechanisms during a flaring state observed in early 2015. We examined the temporal behavior and broadband spectral energy distributions (SEDs) during the flare. The size of the γ-ray emission region was estimated based on the variability timescale. To explore the multiwavelength properties of S5 0716+714, we employed three one-zone models: the synchrotron self-Compton (SSC) model, the SSC plus external Compton (EC) model, and the SSC plus pp interactions model, to reproduce the SEDs. Our findings indicate that, while the SSC model can describe the SEDs, it requires an extreme Doppler factor. In contrast, the SSC plus EC model successfully fits the SEDs under the assumption of weak external photon fields but requires a high Doppler factor. Additionally, the SSC plus pp interactions model also reproduces the SEDs, with γ-ray emission originating from π0 decay. However, this model leads to a jet power that exceeds the Eddington luminosity, which remains plausible due to the flaring state or the presence of a highly collimated jet.

Keywords: Blazars, Active galactic nuclei, BL Lacertae objects
Pushing the Atacama Large Millimeter/submillimeter Array to the Limit: 140 pc Resolution Observations of a z = 6.6 Quasar─Galaxy Merger Resolve Strikingly Different Morphologies of Dust Continuum and [C II] 158 μm Emission. We present   (140 pc) resolution Atacama Large Millimeter/submillimeter Array observations of [C II] 158 μm and dust continuum emission of the z = 6.6 quasar J0305─3150, resolved over ∼300─400 independent resolution elements. The dust continuum emission is compact with ∼80% recovered within   (1.6 kpc), whereas the [C II] emission profile is composed of a central Gaussian ( , i.e., &lt;2.2 kpc) and an extended component (detected up to ∼10 kpc at &gt;3σ). We infer a direct contribution of the quasar to the observed 260 GHz continuum Sν,QSO/Sν,QSO + Host ≲ 1%. We report the detection of far-infrared (FIR)-detected star-forming clumps with r &lt; 200 pc and properties similar to that of rest-frame UV─optical clumps reported in the literature. The 200 pc resolved [C II]/FIR ratio follows the global relation with the FIR surface brightness established in low- and high-redshift galaxies, even at the quasar location. We find that dust continuum is emitted in regions of   consistent with the size of photodissociation regions (PDRs), whereas 50% of the [C II] originates from larger physical scales (θ ≳ 2″). The large-scale [C II] emission presents a velocity gradient aligned with a nearby companion with perturbed kinematics, and misaligned with the kinematics of the small-scale emission. The absence of significant [C II] emission by structures with physical scale ≲ 1 kpc implies that [C II] emission is not produced in dense PDRs located at the boundary of giant molecular clouds. We argue instead that [C II] is produced in low-density PDRs in the interstellar medium and diffuse H I gas tidally stripped during the ongoing merger.

Keywords: Quasar-galaxy pairs, Millimeter astronomy, Quasars, Interstellar medium, High-redshift galaxies, Interferometry
Improving the Determination of Supernova Cosmological Redshifts by Using Galaxy Groups. At the low-redshift end (z &lt; 0.05) of the Hubble diagram with Type Ia Supernovae (SNe Ia), the contribution to Hubble residual scatter from peculiar velocities (PVs) is of similar size to that due to the limitations of the standardization of the SN Ia light curves. A way to improve the redshift measurement of the SN host galaxy is to utilize the average redshift of the galaxy group, effectively averaging over small-scale/intracluster PVs. One limiting factor is the fraction of SN host galaxies in galaxy groups, previously found to be 30% using (relatively incomplete) magnitude-limited galaxy catalogs. Here, we do the first analysis of N-body simulations to predict this fraction, finding ∼73% should have associated groups and group averaging should improve redshift precision by ∼135 km s‑1 (∼0.04 mag at z = 0.025). Furthermore, using spectroscopic data from the Anglo-Australian Telescope, we present results from the first pilot program to evaluate whether or not 23 previously unassociated SN Ia hosts belong in groups. We find that 91% of these candidates can be associated with groups, consistent with predictions from simulations given the sample size. Combining with previously assigned SN host galaxies in Pantheon+, we demonstrate improvement in Hubble residual scatter equivalent to 145 km s‑1, also consistent with simulations. For new and upcoming low-z samples from, for example, the Zwicky Transient Facility and the Legacy Survey of Space and Time, a separate follow-up program identifying galaxy groups of SN hosts is a highly cost-effective way to enhance their constraining power.

Keywords: Cosmology, Type Ia supernovae, Galaxy groups
Bulge Oscillation Driven by Outflows of Active Galactic Nuclei. I. Fast Outflow Case. There is growing evidence for star formation inside outflows of active galactic nuclei (AGNs). The formed stars are injected into bulges and give rise to perturbation of bulges. In this paper, we investigate the issues of nonrotating, spherically symmetric bulges under the perturbation of fast, massive outflows with stars formed inside. We show that the potential perturbation of outflows, together with injection and dynamical friction of these stars, could drive bulge oscillations. Still, we find that nonzero radial velocity of bulges will be driven by the episodic outflows of AGNs, and after the AGN has quenched, the radial velocity will tend to zero within a timescale ~τAGN, which is the AGN's lifetime. For some typical values of bulges and AGNs, we find that the expansion and contraction velocities are a few × 10 km s‑1 for 1010 M⊙ bulges and mass outflowing rate 500 M⊙ yr‑1, which would give observational signatures.

Keywords: Supermassive black holes, Active galactic nuclei, Galaxies
A UV to X-Ray View of Soft Excess in Type 1 Active Galactic Nuclei. I. Sample Selection and Spectral Profile. A core sample of 59 unobscured type 1 active galactic nuclei (AGNs) with simultaneous XMM-Newton X-ray and UV observations is compiled from the archives to probe the nature of soft X-ray excess (SE). In the first paper of this series, our focus centers on scrutinizing the spectral profile of the soft excess. Of the sources, ≍71% (42/59) exhibit power-law-like (po-like) soft excess, while ≍29% (17/59) exhibit blackbody-like (bb-like) soft excess. We show that a cutoff power law could uniformly characterize both types of soft excesses, with a median Ecut of 1.40 keV for po-like and 0.14 keV for bb-like. For the first time, we report a robust and quantitative correlation between the SE profile and SE strength (the ratio of SE luminosity to that of the primary power-law continuum in 0.5─2.0 keV), indicating that stronger soft excess is more likely to be po-like, or effectively has a higher Ecut. This correlation cannot be explained by ionized disk reflection alone, which produces mostly bb-like soft excess (Ecut ~ 0.1 keV) as revealed by relxilllp simulation. Remarkably, we show with simulations that a toy hybrid scenario, where both ionized disk reflection (relxilllp, with all reflection parameters fixed at default values except for ionization of the disk) and warm corona (compTT, with temperature fixed at 1 keV) contribute to the observed soft excess, can successfully reproduce the observed correlation. This highlights the ubiquitous hybrid nature of the SE in AGNs, and underscores the importance of considering both components while fitting the spectra of soft excess.

Keywords: X-ray active galactic nuclei, Active galactic nuclei
Dark Galactic Subhalos and the Gaia Snail. Gaia has revealed a clear signal of disequilibrium in the solar neighborhood in the form of a spiral (or snail) feature in the vertical phase-space distribution. We investigate the possibility that this structure emerges from ongoing perturbations by dark   Galactic subhalos. We develop a probabilistic model for generating subhalo orbits based on a semianalytic model of structure formation, and combine this framework with an approximate prescription for calculating the response of the disk to external perturbations. We also develop a phenomenological treatment for the diffusion of phase-space spirals caused by gravitational scattering between stars and giant molecular clouds, a process that erases the kinematic signatures of old (t ≳ 0.6 Gyr) events. Perturbations caused by dark subhalos are, on average, orders of magnitude weaker than those caused by luminous satellite galaxies, but the ubiquity of dark halos predicted by cold dark matter makes them a more probable source of strong perturbation to the dynamics of the solar neighborhood. Dark subhalos alone do not cause enough disturbance to explain the Gaia snail, but they excite fluctuations of ∼0.1–0.5 km s‑1 in the mean vertical velocity of stars near the Galactic midplane that should persist to the present day. Subhalos also produce correlations between vertical frequency and orbital angle that could be mistaken as originating from a single past disturbance. Our results motivate investigation of the Milky Way's dark satellites by characterizing their kinematic signatures in phase-space spirals across the Galaxy.

Keywords: Galaxy stellar disks, Stellar dynamics, Dark matter, Gaia
FEASTS: Radial Distribution of H I Surface Densities Down to 0.01 M<SUB>⊙</SUB> pc<SUP>‑2</SUP> of 35 Nearby Galaxies. We present the H I surface density (ΣH I) radial distributions based on total-power H I images obtained by FAST in the FEASTS program, for 35 galaxies with inclinations lower than 72°. We derive the H I radius R001, which is the radius for the 0.01 M⊙ pc‑2 (~1018.1 cm‑2) isodensity level, 100 times deeper than the 1 M⊙ pc‑2 level previously commonly used to measure R1. The profile shapes show a large diversity at a given radius in units of kpc, group virial radius, and R1, but they align more tightly with the radius normalized by R001. The universal H I profile has a scatter of ~0.2 dex and a scale length of ~0.11R001 in the outer region. We derive a new R001–MH I relation, which has a scatter of 0.03 dex and a similar slope of ~0.5 to the previously known R1–MH I relation. Excluding strongly tidal-interacting galaxies, the ratio R001/R1 (anti)correlates strongly and significantly with the H I-to-stellar mass ratio and specific star formation rate, but not with the stellar mass, MH I, dark matter mass, or star formation rate. The strongly tidal-interacting galaxies tend to show deviations from these trends and have the most flattened profiles. These results imply that, in the absence of major tidal interactions, physical processes must cooperate so that ΣH I distributes in a self-similar way in the outer region down to the 0.01 M⊙ pc‑2 level. Moreover, they may drive gas flows in such a way that H I-richer galaxies have H I disks that not only extend further but also transport H I inward more efficiently from R001 to R1.

Keywords: Disk galaxies, Galaxy evolution, Interstellar medium, Circumgalactic medium
Retracing the Cold Plasma Dispersion Law in Pulsar B0329+54: New Insights into Frequency-dependent Dispersion Measures. Multiple studies have investigated potential frequency-dependent dispersion measures (DMs) in PSR B0329+54, with sensitivities at levels of 10‑3 pc cm‑3 or higher, using frequencies below 1 GHz. Utilizing the extensive bandwidth of the upgraded Giant Metrewave Radio Telescope, we conducted simultaneous observations of this pulsar across a frequency range of 300–1460 MHz. Our observations reveal a distinct point in the pulse profile of PSR B0329+54 that appears to align remarkably well with the cold-plasma dispersion law, resulting in a unique measured DM across the entire frequency range. In contrast, using times of arrival from widely adopted pulsar timing techniques (e.g., FFTFIT) leads to frequency-dependent DMs. We investigated the potential causes of these frequency-dependent DMs in this pulsar and their relationship with the underlying magnetic field geometry corresponding to the radio emission. Our study reveals that all frequencies in the range 300–1460 MHz originate from a region no larger than 204 km, and the dipolar magnetic-field geometry model indicates that the emission region is centered at ~800 km from the star. This is the tightest constraint on the size of the emission region reported so far for PSR B0329+54 at the given frequencies, and it is at least 5 times more stringent than the existing emission height constraints based on the dipolar geometry model.

Keywords: Neutron stars, Pulsar timing method, Interstellar medium, Pulsars
Stellar X-Ray Variability and Planetary Evolution in the DS Tucanae System. We present an analysis of four Chandra observations of the 45 Myr old DS Tuc binary system. We observed X-ray variability of both stars on timescales from hours to months, including two strong X-ray flares from star A. The implied flaring rates are in agreement with past observations made with XMM-Newton, though these rates remain imprecise due to the relatively short total observation time. We find a clear, monotonic decline in the quiescent level of the star by a factor of 1.8 across 8 months, suggesting stellar variability that might be due to an activity cycle. If proven through future observations, DS Tuc A would be the youngest star for which a coronal activity cycle has been confirmed. The variation in our flux measurements across the four visits is also consistent with the scatter in empirical stellar X-ray relationships with Rossby number. In simulations of the possible evolution of the currently super-Neptune-sized planet DS Tuc A b, we find a range of scenarios for the planet once it reaches a typical field age of 5 Gyr, from Neptune size down to a completely stripped super-Earth. Improved constraints on the planet's mass in the future would significantly narrow these possibilities. We advocate for further Chandra observations to better constrain the variability of this important system.

Keywords: X-ray astronomy, Exoplanets, Exoplanet astronomy, Stellar astronomy, Exoplanet evolution, Time domain astronomy, Variable stars, Planet hosting stars
Tracking Outflow Using Line Locking (TOLL). II. Large Line-locking Web Identified in Quasar J151352+085555. Quasar outflows often consist of two clouds with velocity separations matching the doublet spacings of common UV resonance transitions, a phenomenon known as line locking, which is commonly observed in quasar spectra. Multiple clouds can be locked together through multi-ion doublets, forming a "line-locking web." In the second paper of the TOLL project, we present the discovery of one of the largest "line-locking webs" known to date from the Very Large Telescope UVES spectra of QSO J151352+085555. We identify 12 associated narrow absorption line systems through the C IV, N V, Si IV, O VI, and multiple Lyman lines (Lyα to Lyϵ) and find 10 out of the 12 absorbers are line-locked together by comparing velocity separations between different absorption systems. By conducting photoionization modeling with CLOUDY, we measure the total hydrogen column densities, metallicities, and ionization parameters of these absorbers, which suggests that the absorbers likely have subsolar metallicities. A preliminary statistical analysis demonstrates that the shadowed clouds tend to have similar ionization states compared to the shadowing ones. Identification of one of the largest line-locking webs implies that radiative acceleration plays an important role in sorting out cloud velocities in quasar outflows and highlights the need for more sophisticated theoretical models to explain its formation and evolution.

Keywords: Quasar absorption line spectroscopy
Hybrid Simulations of Interstellar Pickup Ions at the Solar Wind Termination Shock Revisited. We revisit previous hybrid simulations of the heating and acceleration of interstellar pickup ions (PUIs) at the solar wind termination shock. In previous simulations, a relatively cold initial distribution of PUIs was assumed; and while the resulting shock-heated distribution was consistent with Voyager 2 LECP measurements at about 30 keV, the intensity of the distribution downstream of the shock in the ~1–10 keV energy range was lower than predictions based on analysis of energetic neutral atoms (ENAs) from the Interstellar Boundary Explorer-Hi and Cassini's Ion and Neutral Camera. Here we perform new simulations with more realistic initial PUI distributions. We assume the distribution is a partially filled spherical shell in velocity space with a radius that varies from 320 to 640 km s‑1. We then use the distributions downstream of the shock from these new simulations to estimate the ENA flux spectrum and compare with observations. We find that the predicted ENA spectrum from the new simulations much better matches the observations over a broad range of energies. We conclude that the hybrid simulations provide reasonable predictions for the distribution of charged particles in the energy range from ~0.5 to 50 keV.

Keywords: Pickup ions, Termination shock, Cosmic rays