Sazuna/UAT_keywords huggingface dataset:
The Importance of Tidal Forces in Molecular Cloud Dynamics. We investigate the role of tidal forces in molecular cloud formation by examining how apparent boundedness, as diagnosed by the classical virial parameter, relates to the actual gravitational state of clouds subject to tidal forces from their environment. Clouds are identified by a dendrogram algorithm in zoom-in regions taken from a simulation of a Milky Way–mass galaxy with the Voronoi mesh code AREPO that resolves star-forming regions at subparsec resolution. To look at a range of environments, we use data from three different regions that evolve differently in the center, near the equivalent of the solar circle, and the outskirts of the modeled galaxy, at three different times, each spaced 2 Myr apart. We compute the importance of tidal forces on all identified clouds. We then compare the boundedness of clouds, including only their internal potentials, to boundedness also including the external gravitational potential. This comparison shows that tidal forces can unbind apparently bound clouds and bind apparently unbound clouds. We characterize the cloud population by comparing their virial parameters to their surface densities, finding the ratio of the maximum to the minimum eigenvalues of the tidal tensor, and determining the strength of gravitational instability in each examined region. We find that it is necessary to take the total gravitational potential into account rather than just the internal self-gravity of the clouds to have an accurate understanding of cloud dynamics.

Keywords: Hydrodynamical simulations, Disk galaxies, Giant molecular clouds, Interstellar medium, Tides
Elastic Planetoids. Modeling the internal structure of self-gravitating solid and liquid bodies presents a challenge, as existing approaches are often limited to either overly simplistic constant-density approximations or more complex numerical equations of state (EOSs). We present a detailed analysis of a tractable and physically motivated model for perfectly elastic, spherically symmetric self-gravitating bodies in hydrostatic equilibrium. The model employs a logarithmic equation of state (often referred to as a logotropic EOS) with a nonzero initial density and constant bulk modulus. Importantly, the scaling properties of the model allow all solutions to be derived from a single, universal solution of an ordinary differential equation, resembling the Lane–Emden and Chandrasekhar models. The model provides new insights into stability issues and reveals oscillatory asymptotic behavior in the mass–radius relation, including the existence of both a maximum mass and a maximum radius. We derive useful, simple analytical approximations for key properties, such as central overdensity, moment of inertia, binding energy, and gravitational potential, applicable to small, metallic bodies like asteroids and moons. These new approximations could aid future research, including space mining and the scientific characterization of small solar system bodies.

Keywords: Gravitational equilibrium, Gravitational instability, Asteroids, Small Solar System bodies, Solid matter physics
Two-component γ-Ray Emission Spectrum and X-Ray Polarization of the Radio Galaxy Pictor A. Pictor A is a γ-ray emitting radio galaxy and has a bright hotspot called the western hotspot (WHS), located ∼4' away from the nucleus. In this work, we present an analysis of its 16 yr Fermi Large Area Telescope (LAT) data and report the Imaging X-ray Polarimetry Explorer (IXPE) observations for this source. Our analysis of the Fermi-LAT observations reveals evidence of two components in the average γ-ray spectrum of Pictor A, exhibiting a statistically significant hardening from Γγ,1 = 3.25 ± 0.15 to Γγ,2 = 1.81 ± 0.07 at a break energy of 2.46 ± 0.09 GeV. Notably, variability of γ-rays is evident in Pictor A, predominantly driven by the component below the break energy, while the component above the break energy remains stable. Furthermore, our analysis reveals that a power-law function provides an adequate fit for the high-flux-state spectrum, while a broken-power-law function remains necessary to accurately model the low-flux-state spectrum. We suggest that the low-energy component originates from the nucleus, while the high-energy component primarily stems from WHS. The broadband spectral energy distributions of both nucleus and WHS can be well represented by a simple leptonic model, with both γ-ray components attributed to the synchrotron self-Compton (SSC) process. Analysis of IXPE data provides upper limits on the polarization degree of ΠX &lt; 6.6% for the nucleus and ΠX &lt; 56.4% for the WHS within the 2–8 keV band. For the nucleus, this result aligns with X-ray emission originating from the SSC process. However, the upper limit of ΠX &lt; 56.4% for WHS is insufficient to conclusively determine the X-ray emission mechanism in this region.

Keywords: Spectropolarimetry, Relativistic jets, Radio galaxies, Non-thermal radiation sources, X-ray active galactic nuclei
Cosmic-Ray Diffusion in the Turbulent Interstellar Medium: Effects of Mirror Diffusion and Pitch-angle Scattering. Cosmic rays (CRs) interact with turbulent magnetic fields in the interstellar medium (ISM), generating nonthermal emission. After many decades of studies, the theoretical understanding of their diffusion in the ISM continues to pose a challenge. This study numerically explores a recent prediction termed "mirror diffusion" and its synergy with the traditional diffusion mechanism based on gyroresonant scattering. Our study combines 3D MHD simulations of star-forming regions with test particle simulations to analyze CR diffusion. We demonstrate the significance of mirror diffusion in CR diffusion parallel to the magnetic field when the mirroring condition is satisfied. Our results support the theoretical expectation that the resulting particle propagation arising from mirror diffusion in combination with much faster diffusion induced by gyroresonant scattering resembles a Levy-flight-like propagation. Our study highlights the necessity to reevaluate the diffusion coefficients traditionally adopted in the ISM based on gyroresonant scattering alone. For instance, our simulations imply a diffusion coefficient ∼1027 cm2 s─1 for particles with a few hundred TeV within regions spanning a few parsecs around the source. This estimate is in agreement with gamma-ray observations, which show the relevance of our results for the understanding of gamma-ray emission in star-forming regions.

Keywords: Magnetohydrodynamics, Interstellar medium, Magnetic fields, Particle astrophysics, Cosmic rays
On the Nature of the Bright Front of Solar Coronal Mass Ejections. A new explanation has been proposed on the nature of the three-part (bright core, dark cavity, and bright front) structure of coronal mass ejections (CMEs). It suggests that the bright front originates from the plasma pileup along the overlying coronal loops rather than the boundary of the magnetic flux rope at the early eruption stage. This has been confirmed with an active-region event through the direct comparison between the EUV loops and the CME front. However, large-scale EUV loops are hardly observed outside of strong active regions; thus, the front nature remains unclear for CMEs from quiet-Sun regions or weak active regions. In this paper, we address this issue through an intermediate filament eruption from a plage region without sunspots on 2024 March 30. Combining the overlapping observations of the Atmospheric Imaging Assembly and K-Coronagraph, we find that the overlying coronal loops appear gradually in EUV images during the filament eruption. The compressed loops and the plasma pileup along the loops (171 Å) correspond to the CME front in white-light images, which is essentially similar to the situation of events from strong active regions. Therefore, we believe that the explanation on the CME front holds true regardless of whether the EUV loops are visible or not prior to the eruption, and it works for events from different regions, including active regions and quiet-Sun regions. The reasons why the density evolution with height does not support or deny the pileup are discussed.

Keywords: Solar activity, Solar flares, Solar coronal mass ejections
Luminosity Function of Galaxies in Voids: A Modification Inspired by Excursion Set Theory. In the standard picture of cosmology, the galaxies reside in dark matter (DM) halos. DM halos are distributed in the cosmic web in different environments. The luminosity of the galaxies in different environments can be used as a probe to assess a cosmological model. This study focuses on the properties of galaxies in void regions, where halos typically do not experience extreme conditions. By examining the galaxy luminosity function, we aim to understand the dependence of galaxy properties on their environment and redshift so that later, we can use this as a tool to evaluate cosmological models. We employ the excursion set theory to incorporate parameters related to the number density of DM halos into the luminosity function. Using the Galaxy and Mass Assembly survey and 2dFGRS data sets, we fit our theoretical models to observational data, examining the environmental and redshift dependence of the galaxy luminosity function. Our results indicate that we model the galaxy luminosity function in voids effectively by considering the linear density contrast of the environment and the growth function D(z) for redshift dependence. This study provides a model for the environmental dependence of galaxy luminosity function that offers an improvement in the χ2 parameter compared to the previously proposed model in T. McNaught-Roberts et al. Both Bayesian information criterion (BIC) and Akaike information criterion (AIC) tests support the superiority of this model for the void region.

Keywords: Luminosity function, Galaxy dark matter halos, Voids, Large-scale structure of the universe
The Proper Motion of Strongly Lensed Binary Neutron Star Mergers in LIGO/Virgo/Kagra Can Be Constrained by Measuring Doppler-induced Gravitational-wave Dephasing. Strongly lensed binary neutron star (NS–NS) mergers are expected to be observed once LIGO/Virgo/Kagra reaches the planned A+ or proposed A# sensitivity. We demonstrate that the relative transverse velocity of the source-lens system can be constrained by comparing the phase of the two associated gravitational wave (GW) images, using both semianalytical and numerical Bayesian methods. For A+ sensitivity, a 1σ NS–NS merger signal in magnification (μ = 200) and redshift (zS = 1) will carry a marginally detectable dephasing signature for a source transverse velocity of ∼1800 km s‑1. This is comparable to the velocity dispersion of large galaxy clusters. Assuming the same population distribution, the most likely source parameters of μ = 100 and zS = 1.4 are always expected to showcase detectable dephasing imprints for A# sensitivity, provided they are moving with transverse velocities larger than ∼ 2000 km s‑1. We conclude that a first measurement of the relative transverse velocity of a source via GW dephasing methods is likely only a few years away.

Keywords: Neutron stars, Strong gravitational lensing, Gravitational wave astronomy, Gravitational lensing, Gravitational waves
The Virial Factor f of the Hβ Broad Line for NGC 5548 and NGC 4151. The variability of virial factor f is investigated for two active galactic nuclei, NGC 5548 and NGC 4151, which had been previously reverberation mapped (RM) over 20 times in the past 30 yr. Using four velocity tracers from the broad Hβ width at half-maximum (FWHMHβ) or the line dispersion from the mean or rms spectra, f for each RM epoch is calculated. Significant correlations are found between f and observational parameters, such as the broad-line widths, the Eddington ratios, and the line profile shapes. For NGC 5548,  f∝FWHMmean‑0.70±0.13  and for NGC 4151,  f∝FWHMmean‑3.31±0.59 . This suggests that a variable f should be included to weight the virial supermassive black hole mass. Using a simple model of thick-disk broad-line regions (BLRs), we show that changes in mean inclination can explain f variation. The inclination range is 14 .° 1‑40 .° 6 for NGC 5548 and 14 .° 0‑55 .° 1 for NGC 4151. Modeling the light curves of f with a damped random walk process yields mean timescales of 638 and 668 days, consistent with BLR dynamical timescales within uncertainties. This indicates that f variations are linked to BLR dynamics, likely due to changes in geometry or inclination.

Keywords: Supermassive black holes, Reverberation mapping, Active galactic nuclei
On Fast-radio-burst-associated X-Ray Bursts: Inverse Compton Scattering of Radio Photons by an Extreme Pair Flow During Magnetosphere Activities. The Galactic fast radio burst (FRB) FRB 200428 was associated with a short X-ray burst (XRB) from the magnetar SGR J1935+2154 during one of its active phases. This FRB-associated XRB exhibits distinct properties compared to other typical XRBs, including a significantly higher cutoff energy and a steeper power-law index. Its recovered X-ray light curve shows a multiple-peak structure, with the time of arrival offset from that of the FRB. These unique features imply a special physical link between the FRB and X-ray emissions. In 2022 October, a similar FRB–XRB association was detected from the same source. In this paper, we propose a model in which the observed spectral and temporal features of the associated XRBs can be attributed to the inverse Compton scattering (ICS) of FRB photons by an extreme pair flow around the light cylinder, with a bulk Lorentz factor of Γ ∼ 10 and a power-law distribution in the comoving frame, characterized by a typical Lorentz factor  γm'∼5×104 . This extreme pair flow could originate from the compression of a transient pulse of ∼1040‑1041 erg s‑1 and the acceleration through magnetic reconnection in the current sheet during magnetar activity. The Doppler-boosted ICS spectra and the arrival time shifts in such a scenario can well explain the observed features of the FRB 200428–associated XRB and can also account for another associated event in 2022.

Keywords: Magnetars, Non-thermal radiation sources, X-ray bursts, Radio transient sources
Magellanic Accretion-powered Pulsars Studied via an Unscented Kalman Filter. Magnetized high-mass X-ray binary pulsars accreting from a surrounding disk have been recently studied by a time-dependent Kalman filter (KF) model of accretion capable of studying correlations between dynamical variables and producing time series of their behaviors. We return to the intrinsic KF equations that describe the accretion process, and we rewrite them in simpler forms that allow for straightforward interpretations and a deeper understanding of the KF output data. We describe the influence of the KF defined frequencies β1, β2, and γΩ, and we investigate the surface dipolar magnetic fields of 24 Magellanic pulsars produced by the KF analysis in comparison to the values obtained from standard accretion theory using the long-term trending changes of the pulsar spin periods (known as the long-term P-dot values). Good agreement is obtained over a wide range of pulsar spin periods when the KF magnetic field values are scaled down to the propeller regime by a factor of  1‑ωs , where ωs = β2/β1 is the fastness parameter that also distinguishes the regime of "stable polar" accretion (ωs &gt; 0.6) from Rayleigh–Taylor-driven "two-tongue equatorial" (ωs &lt; 0.45) matter inflow.

Keywords: Pulsars, High mass x-ray binary stars, Magnetic fields, Astronomical instrumentation
Persistent Radio Sources Associated with Fast Radio Bursts: Implications from Magnetar Progenitors. The rare association of three persistent radio sources (confirmed PRS1 and PRS2, candidate PRS3) with repeating fast radio bursts (FRB 20121102A, 20190520B, 20201124A) offers a unique probe into their magneto-ionic environments. PRSs are attributed to synchrotron emission from relativistic charged particles of a magnetar wind nebula (MWN), powered by spin-down magnetohydrodynamic wind or internal magnetic field decay. Using a multizone hydrodynamic model, we track MWN evolution to constrain magnetar progenitor properties. For PRS1 and PRS2, we find an equipartition radius Req ∼ 0.1 pc that is consistent with the radio scintillation estimates (&gt;0.03 pc) and radio imaging limits (&lt;0.7 pc). This compact size favors low expansion speeds and large initial spin periods, Pi ≳ 10 ms, ruling out millisecond magnetar progenitors. Given Pi ≳ 10 ms, a current size of ∼0.1 pc, a supernova kinetic energy  ESN∼1050–1051  erg, and an ejecta mass M ∼ 3–10 M⊙, the PRS age is t ∼ 10–102 yr. PRSs with t &gt; 20 yr require an internal field (Bint ∼ 1016–1016.5 G) with a decay timescale td ∼ 10–102.5 yr. The slowest field decay ( td,max∼500  yr) favors subenergetic supernovae ( ESN∼1050  erg) with massive ejecta (M ≳ 10 M⊙) and a low-ionization fraction (∼3%). For the subenergetic scenario, for the confirmed PRSs, we predict a cooling break at 100–150 GHz at 20–40 μJy and self-absorption near 200 MHz at 180 μJy. For PRS3, a rotation-powered MWN is viable only if t ∼ 10 yr; an inverted spectrum beyond 150 GHz would rule out this scenario.

Keywords: Radio continuum emission, Neutron stars, Radio bursts, Radio transient sources
H I Absorption Line and Anomalous Dispersion in the Radio Pulses of PSR B1937+21. We use the Five-hundred-meter Aperture Spherical radio Telescope to observe the bright millisecond pulsar PSR B1937+21 (J1939+2134) and record the data in the band from 1.0 to 1.5 GHz. We measure the neutral hydrogen (H I) emission and absorption lines near 1420 MHz (λ ≃ 21 cm). We derive the kinematic distance of the pulsar with the H I observation. By comparing this with the archival absorption spectra observed decades ago, we notice possible variations in the absorption spectra toward this pulsar, which correspond to a possible tiny-scale atomic structure of a few astronomical units in size. We also verify the apparent faster-than-light anomalous dispersion at the H I absorption line of this pulsar previously reported.

Keywords: Radio spectroscopy, Pulsar timing method, Neutral hydrogen clouds, H I line emission, Radio pulsars
On the Origins of "Hostless" Supernovae: Testing the Faint-end Galaxy Luminosity Function and Supernova Progenitors with Events in Dwarf Galaxies. We present arguments on the likely origins of supernovae without associated host galaxies from open field, nonclustered environments. We show why it is unlikely these "hostless" supernovae stem from escaped hypervelocity stars in any appreciable numbers, or the extreme outer halos of large galaxies, especially for core-collapse supernovae. It is highly likely that hostless events arise from dwarf host galaxies too faint to be detected in their parent surveys. Several detections and numerous upper limits suggest a large number of field dwarfs, to MV &gt; ‑14, which themselves may be important to constraining the slope of the low-mass end of the UV luminosity function, understanding galaxy evolution, and putting Lambda cold dark matter (ΛCDM) into context. Moreover, the detailed study of these mass- and metallicity-constrained host environments, and the variety of supernovae that occur within them, could provide more stringent constraints on the nature of progenitor systems.

Keywords: Hypervelocity stars, Dwarf galaxies, Supernovae
Magnification Bias Reveals Severe Contamination in Hubble Frontier Field Photo-z Catalogs. Gravitational lensing by massive galaxy clusters enables faint distant galaxies to be more abundantly detected than in blank fields, thereby allowing one to construct galaxy luminosity functions (LFs) to an unprecedented depth at high redshifts. Intriguingly, photometric redshift catalogs constructed from the Hubble Frontier Fields survey display an excess of z ≳ 4 galaxies in the cluster lensing fields that is not seen in accompanying blank parallel fields. The observed excess, while possibly a gift of gravitational lensing, could also be from misidentified low-z contaminants having similar spectral energy distributions as high-z galaxies. In the latter case, the contaminants may result in nonphysical upturns in UV LFs and/or washed-out faint-end turnovers predicted by contender cosmological models to Lambda cold dark matter (ΛCDM). Here, we employ the concept of magnification bias to perform the first statistical estimation of contamination levels in Hubble Frontier Fields lensing field photometric redshift catalogs. While we were able to reproduce a lower-z lensed sample, it was found ∼56% of the 3.5 &lt; zphot &lt; 5.5 samples are likely low-z contaminants. Widely adopted Lyman-break-galaxy-like selection rules in the literature may give a "cleaner" sample magnification-bias-wise but we warn readers the resulting sample would also be less complete. Individual mitigation of contaminants is arguably the best way to investigate the faint high-z Universe, and this may be made possible with JWST observations.

Keywords: Catalogs
A New Measure of Assembly Bias Using the Environment Dependence of the Luminosity Function. Assembly bias is the variation in the clustering of dark matter halos and galaxies that arises from correlations between the halo assembly history and the large-scale environment at fixed halo mass. In this work, we use the cosmological magnetohydrodynamical simulation TNG300 to investigate how assembly bias affects the environment-dependent galaxy luminosity function (LF). We measure the LFs in bins of large-scale environment for the original simulated galaxy sample and for a shuffled sample, where the galaxies are randomly reassigned among halos of similar mass to remove assembly bias. By comparing them, we find distinct signatures, showing variations in the number of galaxies at the ∼10% level across all luminosities. Assembly bias increases the tendency of galaxies to reside in denser environments and further dilutes underdense regions, beyond the trends governed by halo mass. When separating by color, we see that assembly bias has a much bigger effect on red galaxies fainter than  Mr‑5logh=‑18.5 , which accounts for a ∼20% increase in the number of galaxies in the densest environment and a remarkable 50% decrease in the least dense regions. The ratio of these measurements for the densest and least dense regions provides a significant assembly bias signal for the faint red galaxies, larger than a factor of 2. Overall, our results provide a novel sensitive measure of assembly bias, offering valuable insight for modeling the effect and a potential new route to detect it in observations.

Keywords: Luminosity function, Galaxy dark matter halos, Galaxy formation, Hydrodynamical simulations, Large-scale structure of the universe, Observational cosmology, Galaxy evolution, Galaxy luminosities, Dark matter, Galaxies, Magnetohydrodynamical simulations