Sazuna/UAT_keywords huggingface dataset:
Possibilities and Limitations of Kinematically Identifying Stars from Accreted Ultra-faint Dwarf Galaxies. The Milky Way has accreted many ultra-faint dwarf galaxies (UFDs), and stars from these galaxies can be found throughout our Galaxy today. Studying these stars provides insight into galaxy formation and early chemical enrichment, but identifying them is difficult. Clustering stellar dynamics in 4D phase space (E, L  z , J  r , J  z ) is one method of identifying accreted structure that is currently being utilized in the search for accreted UFDs. We produce 32 simulated stellar halos using particle tagging with the Caterpillar simulation suite and thoroughly test the abilities of different clustering algorithms to recover tidally disrupted UFD remnants. We perform over 10,000 clustering runs, testing seven clustering algorithms, roughly twenty hyperparameter choices per algorithm, and six different types of data sets each with up to 32 simulated samples. Of the seven algorithms, HDBSCAN most consistently balances UFD recovery rates and cluster realness rates. We find that, even in highly idealized cases, the vast majority of clusters found by clustering algorithms do not correspond to real accreted UFD remnants and we can generally only recover 6% of UFDs remnants at best. These results focus exclusively on groups of stars from UFDs, which have weak dynamic signatures compared to the background of other stars. The recoverable UFD remnants are those that accreted recently, z accretion ≲ 0.5. Based on these results, we make recommendations to help guide the search for dynamically linked clusters of UFD stars in observational data. We find that real clusters generally have higher median energy and J  r , providing a way to help identify real versus fake clusters. We also recommend incorporating chemical tagging as a way to improve clustering results.

Keywords: Stellar kinematics, Dwarf galaxies, Stellar dynamics, Clustering, Galaxy accretion
Formation and Morphology of the First Galaxies in the Cosmic Morning. We investigate the formation and morphological evolution of the first galaxies in the cosmic morning (10 ≳ z ≳ 4) using the Horizon Run 5 (HR5) simulation. For galaxies above the stellar mass ${M}_{\star ,\min }=2\times {10}^{9}\,{M}_{\odot }$ , we classify them into disk, spheroid, and irregular types according to their asymmetry and stellar-mass morphology. We find that about two-thirds of the galaxies have a Sérsic index &lt;1.5, reflecting the dominance of disk-type morphology in the cosmic morning. The rest are evenly distributed as incidental and transient irregulars or spheroids. These fractions are roughly independent of redshift and stellar mass up to ~1010 M ⊙. Almost all the first galaxies with ${M}_{\star }\gt {M}_{\star ,\min }$ at z &gt; 4 form at initial peaks of the matter-density field. Large-scale structures in the universe emerge and grow like cosmic rhizomes as the underlying matter-density fluctuations grow and form associations of galaxies in rare overdense regions and the realm of the galactic world is stretched into relatively lower-density regions along evolving filaments. The cosmic web of galaxies forms at lower redshifts when most rhizomes globally percolate. The primordial angular momentum produced by the induced tidal torques on protogalactic regions is correlated with the internal kinematics of galaxies and tightly aligned with the angular momentum of the total galaxy mass. The large-scale tidal field imprinted in the initial conditions seems responsible for the dominance of disk morphology and for the tendency of galaxies to reacquire a disk postdistortion.

Keywords: Galaxy formation, Galaxy evolution
CLEAR: The Evolution of Spatially Resolved Star Formation in Galaxies between 0.5 ≲ z ≲ 1.7 Using Hα Emission Line Maps. Using spatially resolved Hα emission line maps of star-forming galaxies, we study the spatial distribution of star formation over a wide range in redshift (0.5 ≲ z ≲ 1.7). Our z ~ 0.5 measurements come from deep Hubble Space Telescope (HST) Wide Field Camera 3 G102 grism spectroscopy obtained as part of the CANDELS Lyα Emission at Reionization Experiment. For star-forming galaxies with log(M */M ⊙) ≥ 8.96, the mean Hα effective radius is 1.2 ± 0.1 times larger than that of the stellar continuum, implying inside-out growth via star formation. This measurement agrees within 1σ with those measured at z ~ 1 and z ~ 1.7 from the 3D-HST and KMOS3D surveys, respectively, implying no redshift evolution. However, we observe redshift evolution in the stellar mass surface density within 1 kpc (Σ1kpc). Star-forming galaxies at z ~ 0.5 with a stellar mass of log(M */M ⊙) = 9.5 have a ratio of Σ1kpc in Hα relative to their stellar continuum that is lower by (19 ± 2)% compared to z ~ 1 galaxies. Σ1kpc,Hα /Σ1kpc,Cont decreases toward higher stellar masses. The majority of the redshift evolution in Σ1kpc,Hα /Σ1kpc,Cont versus stellar mass stems from the fact that log(Σ1kpc,Hα ) declines twice as much as log(Σ1kpc,Cont) from z ~ 1 to 0.5 (at a fixed stellar mass of log(M */M ⊙) = 9.5). By comparing our results to the TNG50 cosmological magneto-hydrodynamical simulation, we rule out dust as the driver of this evolution. Our results are consistent with inside-out quenching following in the wake of inside-out growth, the former of which drives the significant drop in Σ1kpc,Hα  from z ~ 1 to z ~ 0.5.

Keywords: Star formation, Galaxy evolution, High-redshift galaxies, Galaxy stellar content
Cosmic Reionization on Computers: Physical Origin of Long Dark Gaps in Quasar Absorption Spectra. I explore the properties of "dark gaps"-regions in quasar absorption spectra without significant transmission-with several simulations from the Cosmic Reionization On Computers (CROC) project. The CROC simulations in the largest available boxes (120 cMpc) come close to matching both the distribution of mean opacities and the frequency of dark gaps, but alas not in the same model: the run that matches the mean opacities fails to contain enough dark gaps and vice versa. Nevertheless, the run that matches the dark gap distributions serves as a counterexample to claims in the literature that the dark gap statistics requires a late end to reionization-in that run reionization ends at z = 6.7 (likely too early). While multiple factors contribute to the frequency of large dark gaps in the simulations, the primary factor that controls the overall shape of the dark gap distribution is the ionization level in voids-the lowest-density regions produce the highest transmission spikes that terminate long gaps. As the result, the dark gap distribution correlates strongly with the fraction of the spectrum above the gap detection threshold and the observed distribution is matched by the simulation in which this fraction is 2%. Hence, the gap distribution by itself does not constrain the timing of reionization, although it may do so in combination with the distribution of mean opacities.

Keywords: Reionization
Locations and Morphologies of Jellyfish Galaxies in A2744 and A370. We present a study of the orbits, environments, and morphologies of 13 ram-pressure stripped galaxies in the massive, intermediate redshift (z ~ 0.3-0.4) galaxy clusters A2744 and A370, using MUSE integral-field spectroscopy and Hubble Space Telescope imaging from the Frontier Fields Program. We compare different measures of the locations and morphologies of the stripped sample with a sample of six post-starburst galaxies identified within the same clusters, as well as the general cluster population. We calculate the phase-space locations of all cluster galaxies and carry out a substructure analysis, finding that the ram-pressure stripped galaxies in A370 are not associated with any substructures, but are likely isolated infalling galaxies. In contrast, the ram-pressure stripped galaxies in A2744 are strictly located within a high-velocity substructure, moving through a region of dense X-ray emitting gas. We conclude that their ram-pressure interactions are likely to be the direct result of the merger between two components of the cluster. Finally, we study the morphologies of the stripped and post-starburst galaxies, using numerical measures to quantify the level of visual disturbances. We explore any morphological deviations of these galaxies from the cluster population, particularly the weaker cases that have been confirmed via the presence of ionized gas tails to be undergoing ram-pressure stripping, but are not strongly visually disturbed in the broadband data. We find that the stripped sample galaxies are generally divergent from the general cluster sample, with post-starburst galaxies being intermediary in morphology between stripped galaxies and red passive cluster members.

Keywords: Galaxy clusters, Galaxy environments, Galaxy interactions, Galaxy evolution, Intracluster medium, Post-starburst galaxies, Galaxy encounters
On the Robustness of the Velocity Anisotropy Parameter in Probing the Stellar Kinematics in Milky Way-Like Galaxies: Takeaway from TNG50 Simulation. We analyze the velocity anisotropy of stars in real and energy space for a sample of Milky Way-like galaxies in the TNG50 simulation. We employ different selection criteria, including spatial, kinematic, and metallicity cuts, and make three halo classes ( ${ \mathcal A }$ - ${ \mathcal C }$ ) that show mild-to-strong sensitivity to different selections. The above classes cover 48%, 16%, and 36% of the halos, respectively. We analyze the β radial profiles and divide them into either monotonically increasing radial profiles or ones with peaks and troughs. We demonstrate that halos with monotonically increasing β profiles are mostly from class ${ \mathcal A }$ , while those with peaks/troughs are part of classes ${ \mathcal B }$ and ${ \mathcal C }$ . This means that care must be taken, as the observationally reported peaks/troughs might be a consequence of different selection criteria. We infer the anisotropy parameter β energy space and compare that against the β radial profile. It is seen than 65% of halos with very mild sensitivity to different selections in real space are those for which the β radial and energy profiles are closely related. Consequently, we propose that comparing the β radial and energy profiles might be a novel way to examine the sensitivity to different selection criteria and thus examining the robustness of the anisotropy parameter in tracing stellar kinematics. We compare simulated β radial profiles against various observations and demonstrate that, in most cases, the model diversity is comparable with the error bars from different observations, meaning that the TNG50 models are in good overall agreement with observations.

Keywords: Galaxy stellar halos, Hydrodynamical simulations, Milky Way Galaxy
Nonlinear Outcome of Coagulation Instability in Protoplanetary Disks. I. First Numerical Study of Accelerated Dust Growth and Dust Concentration at Outer Radii. Our previous linear analysis presents a new instability driven by dust coagulation in protoplanetary disks. The coagulation instability has the potential to concentrate dust grains into rings and assist dust coagulation and planetesimal formation. In this series of papers, we perform numerical simulations and investigate the nonlinear outcome of coagulation instability. In this paper (Paper I), we first conduct local simulations to demonstrate the existence of coagulation instability. Linear growth observed in the simulations is in good agreement with the previous linear analysis. We next conduct radially global simulations to demonstrate that coagulation instability develops during the inside-out disk evolution owing to dust growth. To isolate the various effects on dust concentration and growth, we neglect the effects of back-reaction to a gas disk and dust fragmentation in Paper I. This simplified simulation shows that neither back-reaction nor fragmentation is a prerequisite for local dust concentration via the instability. In most runs with weak turbulence, dust concentration via coagulation instability overcomes dust depletion due to radial drift, leading to the formation of multiple dust rings. The nonlinear development of coagulation instability also accelerates dust growth, and the dimensionless stopping time τ s reaches unity even at outer radii (&gt;10 au). Therefore, coagulation instability is one promising process to retain dust grains and to accelerate dust growth beyond the drift barrier.

Keywords: Planetesimals, Protoplanetary disks, Circumstellar disks
CLEAR: The Ionization and Chemical-enrichment Properties of Galaxies at 1.1 &lt; z &lt; 2.3. We use deep spectroscopy from the Hubble Space Telescope Wide-Field-Camera 3 IR grisms combined with broadband photometry to study the stellar populations, gas ionization and chemical abundances in star-forming galaxies at z ~ 1.1-2.3. The data stem from the CANDELS Lyα Emission At Reionization (CLEAR) survey. At these redshifts, the grism spectroscopy measure the [O II] λ λ3727, 3729, [O III]λ λ4959, 5008, and Hβ strong emission features, which constrain the ionization parameter and oxygen abundance of the nebular gas. We compare the line-flux measurements to predictions from updated photoionization models (MAPPINGS V; Kewley et al.), which include an updated treatment of nebular gas pressure, $\mathrm{log}P/k={n}_{e}{T}_{e}$ . Compared to low-redshift samples (z ~ 0.2) at fixed stellar mass, $\mathrm{log}{M}_{* }/{M}_{\odot }\,=$ 9.4-9.8, the CLEAR galaxies at z = 1.35 (1.90) have lower gas-phase metallicity, ${\rm{\Delta }}(\mathrm{log}Z)$ = 0.25 (0.35) dex, and higher ionization parameters, ${\rm{\Delta }}(\mathrm{log}q)$ = 0.25 (0.35) dex, where U ≡ q/c. We provide updated analytic calibrations between the [O III], [O II], and Hβ emission-line ratios, metallicity, and ionization parameter. The CLEAR galaxies show that at fixed stellar mass, the gas ionization parameter is correlated with the galaxy specific star formation rates, where ${\rm{\Delta }}\mathrm{log}q\simeq 0.4\times {\rm{\Delta }}(\mathrm{log}\,\mathrm{sSFR})$ , derived from changes in the strength of galaxy Hβ equivalent width. We interpret this as a consequence of higher gas densities, lower gas covering fractions, combined with a higher escape fraction of H-ionizing photons. We discuss both tests to confirm these assertions and implications this has for future observations of galaxies at higher redshifts.

Keywords: Galaxy formation, Galaxy chemical evolution, Emission line galaxies, Galaxy evolution, Spectroscopy, Interstellar medium, High-redshift galaxies
Magnetohydrodynamic Waves in an Asymmetric Magnetic Slab with Different External Flows. Building on recent studies of the Kelvin-Helmholtz instability (KHI) in the solar atmosphere, we investigate a simple analytical model that can further our understanding of how the presence of bulk flows influences the propagation of magnetohydrodynamic (MHD) waves. Our model builds on a series of recent works on stationary MHD waveguides and looks at a magnetic slab with a density asymmetry, as well as asymmetric background steady flows present in its environment. We obtained approximate solutions to the dispersion relation for the important and applicable limiting cases of a thin or a wide slab, as well as low- and high-β plasmas. We also explored the relation between the angular frequency of trapped MHD waves, the limit for the onset of the KHI, and small parameters describing the flow and density asymmetries. Our analytical investigation is complemented by a numerical analysis for various bulk flow speeds and slab widths. Both these avenues of study reveal that the flow field asymmetry has an important effect on both the cutoff frequencies and the stability of trapped MHD waves in the slab configuration.

Keywords: Solar atmosphere, Magnetohydrodynamics, The Sun, Solar magnetic fields, Solar oscillations, Magnetic fields, Solar magnetic bright points
A Semi-empirical Approach to the Dynamic Coupling of CMEs and Solar Wind. Coronal mass ejections (CMEs) are one of the most relevant phenomena for space weather. Moreover, CMEs can negatively affect essential services and facilities. Therefore, to protect society, we require well-grounded knowledge of the physics that governs the propagation of CMEs from near the Sun to the orbit of Earth. In this work, we deduce expressions to approximate the main forces that affect the dynamic coupling between CMEs and the surrounding solar wind. Therefore, we explore the CME-solar wind dynamic coupling from a magnetohydrodynamic perspective, which, combined with a few reasonable assumptions, allows us to obtain expressions for the thermal and magnetic pressure forces, viscous and dynamic drag, and gravity. We simultaneously use our expressions to compute the trajectories of 34 Earth-directed CMEs. Our results, which are compared with in situ data, show significant quantitative consistency; our synthetic transits closely mimic their in situ observed counterparts. We conclude from our results that magnetic, thermal, and dynamic drag significantly surpass the other forces such as dynamic agents of CMEs in the interplanetary medium. In addition, we find that the initial relative speed of CMEs and solar wind is a determinant factor for the dynamic behavior of CMEs. In other words, subsonic CMEs are initially mostly affected by magnetic and thermal pressure forces, whereas super-magnetosonic CMEs are initially governed by inertial drag.

Keywords: Interplanetary medium, Magnetohydrodynamics, Space weather, Solar wind, Solar coronal mass ejections
Influence of Thomson Electron Scattering Redistribution on Spectral Line Polarization Formed in Spherically Symmetric Extended and Expanding Atmospheres. Scattering of line photons by ambient electrons in thermal motion in the stellar atmosphere modifies the wings of both intensity and linear polarization profiles of the spectral lines. The aim of the present paper is to investigate in detail the influence of Thomson electron scattering redistribution on resonance line polarization formed in spherically symmetric extended and expanding atmospheres. A comoving frame method based on the accelerated lambda iteration technique is used to solve the concerned spherically symmetric polarized transfer equation including both the atomic and Thomson electron scattering redistribution functions. Our numerical studies highlight the importance of accounting for Thomson electron scattering redistribution in spectral line polarization problems.

Keywords: Spectropolarimetry, Computational methods, Radiative transfer, Radiative transfer simulations, Stellar atmospheres
FastQSL: A Fast Computation Method for Quasi-separatrix Layers. Magnetic reconnection preferentially takes place at the intersection of two separatrices or two quasi-separatrix layers, which can be quantified by the squashing factor Q, whose calculation is computationally expensive due to the need to trace as many field lines as possible. We developed a method (FastQSL) optimized for obtaining Q and the twist number in a 3D data cube. FastQSL utilizes the hardware acceleration of the graphics processing unit and adopts a step-size adaptive scheme for the most computationally intensive part: tracing magnetic field lines. As a result, it achieves a computational efficiency of 4.53 million Q values per second. FastQSL is open source, and user-friendly for data import, export, and visualization.

Keywords: GPU computing, Solar magnetic fields
Galactic Cosmic-Ray Propagation in the Inner Heliosphere: Improved Force-field Model. A key goal of heliophysics is to understand how cosmic rays propagate in the solar system's complex, dynamic environment. One observable is solar modulation, i.e., how the flux and spectrum of cosmic rays change as they propagate inward. We construct an improved force-field model, taking advantage of new measurements of magnetic power spectral density by Parker Solar Probe to predict solar modulation within the Earth's orbit. We find that modulation of cosmic rays between the Earth and Sun is modest, at least at solar minimum and in the ecliptic plane. Our results agree much better with the limited data on cosmic-ray radial gradients within Earth's orbit than past treatments of the force-field model. Our predictions can be tested with forthcoming direct cosmic-ray measurements in the inner heliosphere by Parker Solar Probe and Solar Orbiter. They are also important for interpreting the gamma-ray emission from the Sun due to scattering of cosmic rays with solar matter and photons.

Keywords: Gamma-ray observatories, Magnetohydrodynamics, High energy astrophysics, Interplanetary turbulence, Plasma astrophysics, Galactic cosmic rays, Solar physics, Gamma-ray astronomy, Particle astrophysics, Cosmic rays
Evidence for the Three Wave Interactions in the Vicinity of an Interplanetary Shock. We present the high time resolution in situ observations of coherent one-dimensional magnetic-field-aligned Langmuir wave packets with well-defined low frequency modulations (beats) in the upstream region of a coronal mass ejection driven supercritical quasi-perpendicular interplanetary (IP) shock. We show that these beat-type waveforms provide what is believed to be the first observational evidence for one of the most important three wave interactions, called the electrostatic decay instability (ESD) $L\to {L}^{{\prime} }+S$ (L is the pump Langmuir wave excited by the shock accelerated electron beam, and L' and S are the daughter Langmuir and ion sound waves, respectively). We also show that (1) the spectra of these wave packets contain the signatures of L, L', and S, which satisfy the resonance conditions required for excitation of ESD, (2) the peak intensities of these wave packets well exceed the ESD threshold values, and (3) the speed of the electron beam estimated using the resonance conditions is very close to the typical observed speeds of the IP shock accelerated electron beams. The implication of these findings is that (1) the shock accelerated electron beams probably are stabilized by the three wave interaction $L\to {L}^{{\prime} }+S$ , and (2) the second harmonic radio emission ${T}_{2{f}_{\mathrm{pe}}}$ of solar type II radio bursts probably is excited by the three wave merging $L+{L}^{{\prime} }\to {T}_{2{f}_{\mathrm{pe}}}$ .

Keywords: Solar physics
Accretion Burst Echoes as Probes of Protostellar Environments and Episodic Mass Assembly. Protostars likely accrete material at a highly time-variable rate, but measurements of accretion variability from the youngest protostars are rare, as they are still deeply embedded within their envelopes. Submillimeter/millimeter observations can trace the thermal response of dust in the envelope to accretion luminosity changes, allowing variations in the accretion rate to be quantified. In this paper, we present contemporaneous submillimeter/millimeter light curves of variable protostars in Serpens Main, as observed by the ALMA Atacama Compact Array (ACA), the Submillimeter Array (SMA), and the James Clerk Maxwell Telescope (JCMT). The most recent outburst of EC 53 (V371 Ser), an ~18 month periodic variable, is well sampled in the SMA and JCMT observations. The SMA light curve of EC 53 is observed to peak weeks earlier and exhibit a stronger amplitude than at the JCMT. Stochastic variations in the ACA observations are detected for SMM 10 IR, with an amplitude a factor of ~2 greater than that seen by the JCMT. We develop a toy model of the envelope response to accretion outbursts to show that EC 53's light curves are plausibly explained by the delay associated with the light travel time across the envelope and the additional dilution of the JCMT response, due to the incorporation of cold envelope material in the beam. The larger JCMT beam can also wash out the response to rapid variations, which may be occurring for SMM 10 IR. Our work thus provides a valuable proof of concept for the use of submillimeter/millimeter observations as a means of probing both the underlying accretion luminosity variations and the protostellar environment.

Keywords: Accretion, Submillimeter astronomy, Eruptive variable stars, Star formation, Protostars