Sazuna/UAT_keywords huggingface dataset:
Probing Coronal Mass Ejection Inclination Effects with EUHFORIA. Coronal mass ejections (CMEs) are complex magnetized plasma structures in which the magnetic field spirals around a central axis, forming what is known as a flux rope (FR). The central FR axis can be oriented at any angle with respect to the ecliptic. Throughout its journey, a CME will encounter interplanetary magnetic fields and solar winds that are neither homogeneous nor isotropic. Consequently, CMEs with different orientations will encounter different ambient medium conditions and, thus, the interaction of a CME with its surrounding environment will vary depending on the orientation of its FR axis, among other factors. This study aims to understand the effect of inclination on CME propagation. We performed simulations with the EUHFORIA 3D magnetohydrodynamic model. This study focuses on two CMEs modeled as spheromaks with nearly identical properties, differing only by their inclination. We show the effects of CME orientation on sheath evolution, MHD drag, and nonradial flows by analyzing the model data from a swarm of 81 virtual spacecraft scattered across the inner heliospheric. We have found that the sheath duration increases with radial distance from the Sun and that the rate of increase is greater on the flanks of the CME. Nonradial flows within the studied sheath region appear larger outside the ecliptic plane, indicating a "sliding" of the interplanetary magnetic field in the out-of-ecliptic plane. We found that the calculated drag parameter does not remain constant with radial distance and that the inclination dependence of the drag parameter cannot be resolved with our numerical setup.

Keywords: Solar physics, Solar coronal mass ejections, Heliosphere, Magnetohydrodynamical simulations
Core Formation by Binary Scouring and Gravitational Wave Recoil in Massive Elliptical Galaxies. Scouring by supermassive black hole (SMBH) binaries is the most accepted mechanism for the formation of the cores seen in giant elliptical galaxies. However, an additional mechanism is required to explain the largest observed cores. Gravitational-wave (GW) recoil is expected to trigger further growth of the core, as subsequent heating from dynamical friction of the merged SMBH removes stars from the central regions. We model core formation in massive elliptical galaxies from both binary scouring and heating by GW recoil and examine their unique signatures. We aim to determine whether the nature of cores in 3D space density can be attributed uniquely to either process and whether the magnitude of the kick can be inferred. We perform N-body simulations of galactic mergers of multicomponent galaxies, based on the observed parameters of four massive elliptical galaxies with cores &gt;0.5 kpc. After binary scouring and hardening, the merged SMBH remnant is given a range of GW recoil kicks with 0.5–0.9 of the escape speed of the galaxy. We find that binary scouring alone can form the cores of NGC 1600 and A2147-BCG, which are &lt;1.3 kpc in size. However, the &gt;2 kpc cores in NGC 6166 and A2261-BCG require heating from GW recoil kicks of &lt;0.5 of the galaxy escape speed. A unique feature of GW recoil heating is flatter cores in surface brightness, corresponding to truly flat cores in 3D space density. It also preferentially removes stars on low angular momentum orbits from the galactic nucleus.

Keywords: Black hole physics, Computational astronomy, Galaxy dynamics, Galaxy nuclei, Giant elliptical galaxies, Gravitational waves
Fast Downflows Observed during a Polar Crown Filament Eruption. Solar filaments can undergo eruptions that result in the formation of coronal mass ejections, which can significantly impact planetary space environments. Observations of eruptions involving polar crown filaments, situated in the polar regions of the Sun, are limited. In this study, we report a polar crown filament eruption (SOL2023-06-12), characterized by fast downflows below the filament. The downflows appear instantly after the onset of the filament eruption and persist for approximately 2 hr, exhibiting plane-of-sky velocities ranging between 92 and 144 km s‑1. They originate from the leading edge of the filament, and no clear acceleration is observed. Intriguingly, these downflows appear at two distinct sites, symmetrically positioned at the opposite ends of the conjugate flare ribbons. Based on the observations, we propose that the filament might be supported by a magnetic flux rope (MFR), and these downflows possibly occur along the legs of the MFR. The downflows likely result from continuous reconnections between the MFR and the overlying magnetic field structures and could either be reconnection outflows or redirected filament materials. We also observed horizontal drifting of the locations of downflows, which might correspond to the MFR's footpoint drifting. This type of downflow can potentially be utilized to track the footpoints of MFRs during eruptions.

Keywords: Solar filament eruptions
Anatomy of the Star Formation in a Tidally Disturbed Disk Galaxy: NGC 3718. We present a UV, optical, and near-IR study of the star-forming complexes in the nearby peculiar galaxy NGC 3718, using Ultraviolet Imaging telescope, Galaxy Evolution Explorer, Spitzer, and DECam Legacy Survey imaging data. The galaxy has a disturbed optical morphology owing to the multiple tidal arms, the warped disk, and the prominent curved dust lanes, but in the near-IR it appears to be a bulge-dominated galaxy. Its disturbed morphology makes it an excellent case to study star formation in a tidally disturbed galaxy that may have undergone a recent minor merger. To study the distribution and properties of the star-forming clumps (SFCs), we divided the galaxy within the R 25 (B band) radius into three parts—the upper, central, and lower regions. Using the UV band images, we investigated the warped star-forming disk, the extended tidal arms, and the distribution and sizes of the 182 SFCs. Their distribution is 49, 60, and 73 in the galaxy's upper, central, and lower regions, respectively. We determined the UV color, star formation rates (SFRs), star formation density (ΣSFR), and ages of the SFCs. The central disk of the galaxy has a larger mean ΣSFR that is ∼3.3 and ∼1.6 times higher than the upper and lower regions, respectively. We also find that the SFCs in the central disk are older than those in the tidal arms. Our study thus shows that minor mergers can trigger the inside-out growth of galaxy disks, where the younger SFCs are in outer tidal arms and not in the inner disk.

Keywords: Galaxy structure, Galaxy interactions, Galaxy photometry, Star formation, Galaxy evolution
Formation of Close-in Neptunes around Low-mass Stars through Breaking Resonant Chains. Conventional planet formation theories predict a paucity of massive planets around small stars, especially very low-mass (0.1‑0.3 M ⊙) mid-to-late M dwarfs. Such tiny stars are expected to form planets of terrestrial sizes but not much bigger. However, this expectation is challenged by the recent discovery of LHS 3154 b, a planet with period of 3.7 days and minimum mass of 13.2 M ⊕ orbiting a 0.11 M ⊙ star. Here, we propose that close-in Neptune-mass planets like LHS 3154 b formed through an anomalous series of mergers from a primordial compact system of super-Earths. We perform simulations within the context of the "breaking the chains" scenario, in which super-Earths initially form in tightly spaced chains of mean-motion resonances before experiencing dynamical instabilities and collisions. Planets as massive and close-in as LHS 3154 b (M  p  ∼ 12‑20 M ⊕, P &lt; 7 days) are produced in ∼1% of simulated systems, in broad agreement with their low observed occurrence. These results suggest that such planets do not require particularly unusual formation conditions but rather are an occasional by-product of a process that is already theorized to explain compact multiplanet systems. Interestingly, our simulated systems with LHS 3154 b-like planets also contain smaller planets at around ∼30 days, offering a possible test of this hypothesis.

Keywords: Exoplanet formation
A Close Pair of Orbiters Embedded in a Gaseous Disk: The Repulsive Effect. We develop a theoretical framework and use 2D hydrodynamical simulations to study the repulsive effect between two close orbiters embedded in an accretion disk. We consider orbiters on fixed Keplerian orbits with masses low enough to open shallow gaps. The simulations indicate that the repulsion is larger for more massive orbiters and decreases with the orbital separation and the disk's viscosity. We use two different assumptions to derive theoretical scaling relations for the repulsion. A first scenario assumes that each orbiter absorbs the angular momentum deposited in its horseshoe region by the companion's wake. A second scenario assumes that the corotation torques of the orbiters are modified because the companion changes the underlying radial gradient of the disk surface density. We find a substantial difference between the predictions of these two scenarios. The first one fails to reproduce the scaling of the repulsion with the disk viscosity and generally overestimates the strength of the repulsion. The second scenario, however, gives results that are broadly consistent with those obtained in the simulations.

Keywords: Exoplanet dynamics, Hydrodynamical simulations, Planetary-disk interactions, Active galactic nuclei, Protoplanetary disks, Planetary migration
Shock-induced Partial Alignment in Geometrically Thick Tilted Accretion Disks Around Black Holes. We carry out idealized three-dimensional general-relativistic magnetohydrodynamic simulations of prograde, weakly magnetized, and geometrically thick accretion flows where the gas distribution is misaligned from the black hole (BH) spin axis. We evolve the disk for three BH spins: a = 0.5, 0.75, and 0.9375, and we contrast them with a standard aligned disk simulation with a = 0.9375. The tilted disks achieve a warped and twisted steady-state structure, with the outer disk misaligning further away from the BH and surpassing the initial 24° misalignment. However, closer to the BH, there is evidence of partial alignment, as the inclination angle decreases with radius in this regime. Standing shocks also emerged in proximity to the BH, roughly at ∼6 gravitational radii. We show that these shocks act to partially align the inner disk with the BH spin. The rate of alignment increases with increasing BH spin magnitude, but in all cases is insufficient to fully align the gas before it accretes. Additionally, we present a toy model of orbit crowding that can predict the location of the shocks in moderate-to-fast rotating BHs, illustrating a potential physical origin for the behavior seen in simulations—with possible applications in determining the positions of shocks in real misaligned astrophysical systems.

Keywords: Accretion, Black hole physics, Magnetohydrodynamics, General relativity, Magnetohydrodynamical simulations
The Effects of Turbulence on Heliosheath Ions and Implications for Energetic Neutral Atoms. The distribution of ions in the heliosheath—the region between the heliospheric termination shock and the heliopause—is important for understanding remote observations of energetic neutral atoms (ENAs). The ion distributions were estimated previously based on hybrid simulations of the heating and evolution of solar wind and interstellar pickup ions across the solar wind termination shock, but these estimates only provide the distributions near the shock. In this work, we use self-consistent hybrid kinetic simulations to investigate the effects of turbulence on ion distributions in the heliosheath. The simulations are compared against Voyager observations, constraining the feasible amplitude and compressibility of turbulence. We find that the heating due to turbulent dissipation can lead to a significant increase in the temperature of thermal solar wind ions. Both turbulent velocity fluctuations and the heating of solar wind ions increase the charge-exchange source for ENAs at low energies (around 100 eV), where current ENA models underpredict observations by more than an order of magnitude. However, the effects of turbulence are likely not strong enough to fully explain these discrepancies.

Keywords: Interplanetary turbulence, Pickup ions, Heliosheath, Heliosphere
Formation of GW230529 from Isolated Binary Evolution. In this paper, we explore the formation of the mass-gap black hole-neutron star (mgBHNS) merger detected in gravitational wave (GW) event, i.e., GW230529, from the isolated binary evolution channel, and study potential signatures of its electromagnetic counterparts. By adopting the "delayed" supernova prescription and reasonable model realizations, our population synthesis simulation results can simultaneously match the rate densities of mgBHNS and total BHNS mergers inferred from the population analyses, along with the population distribution of the BH mass in BHNS mergers reported by the LIGO–Virgo–KAGRA Collaboration. Because GW230529 contributes significantly to the inferred mgBHNS rate densities, we suggest that GW230529 can be explained through the isolated binary evolution channel. Considering the AP4 (DD2) equation of state, the probability that GW230529 can make tidal disruption is 12.8% (63.2%). If GW230529 is a disrupted event, its kilonova peak apparent magnitude is predicted ∼23–24 mag, and hence, can be detected by the present survey projects and Large Synoptic Survey Telescope. Since GW230529 could be an off-axis event inferred from the GW observation, its associated gamma-ray burst (GRB) might be too dim to be observed by γ-ray detectors, interpreting the lack of GRB observations. Our study suggests the existence of mgBHNS mergers formed through the isolated binary evolution channel due to the discovery of GW230529, indicating that BHNS mergers are still likely to be multimessenger sources that emit GWs, GRBs, and kilonovae. Although mgBHNS mergers account for ∼50% of the cosmological BHNS population, we find that ≳90% of disrupted BHNS mergers are expected to originate from mgBHNS mergers.

Keywords: Neutron stars, Gravitational waves, Black holes
Lyα Profile Shape as an Escape-fraction Diagnostic at High Redshift. While the shape of the Lyα profile is viewed as one of the best tracers of ionizing-photon escape fraction (f esc) within low-redshift (z ∼ 0.3) surveys of the Lyman continuum, this connection remains untested at high redshift. Here, we combine deep, rest-UV Keck/LRIS spectra of 80 objects from the Keck Lyman Continuum Spectroscopic Survey with rest-optical Keck/MOSFIRE spectroscopy in order to examine potential correlations between Lyα profile shape and the escape of ionizing radiation within z ∼ 3 star-forming galaxies. We measure the velocity separation between double-peaked Lyα emission structure (v sep), between red-side Lyα emission peaks and systemic (v Lyα,red), and between red-side emission peaks and low-ionization interstellar absorption lines (v Lyα‑LIS). We find that the IGM-corrected ratio of ionizing to nonionizing flux density is significantly higher in KLCS objects with lower v Lyα,red. We find no significant trend between measures of ionizing-photon escape and v Lyα‑LIS. We compare our results to measurements of z ∼ 0.3 "Green Peas" from the literature and find that KLCS objects have larger v sep at fixed v Lyα,red, larger f esc at fixed v Lyα,red, and higher v Lyα,red overall than z ∼ 0.3 analogs. We conclude that the Lyα profile shapes of our high-redshift sources are fundamentally different, and that measurements of profile shape such as v Lyα,red map on to f esc in different ways. We caution against building reionization-era f esc diagnostics based purely on Lyα profiles of low-redshift dwarf galaxies. Tracing v sep, v Lyα,red, and f esc in a larger sample of z ∼ 3 galaxies will reveal how these variables may be connected for galaxies at the epoch of reionization.

Keywords: Optical astronomy, Galaxy evolution, Lyman-alpha galaxies, Reionization, High-redshift galaxies, Near infrared astronomy
Evolving Outer Heliosphere: Tracking Solar Wind Transients from 1 au to the VLISM with IBEX and Voyager 1. Interstellar Boundary Explorer (IBEX) observations of energetic neutral atom (ENA) fluxes from the heliosphere have greatly enriched our understanding of the interaction of the solar wind (SW) with the local interstellar medium (LISM). However, there has been recent controversy surrounding the inability of most ENA models to produce as high an intensity of ∼0.5─6 keV ENAs as IBEX observes at 1 au, especially as a function of time. In our previous study (E. J. Zirnstein et al.), we introduced a new model that utilizes a data-driven magnetohydrodynamic simulation of the SW─LISM interaction to propagate pickup ions through the heliosheath (HS) after they are nonadiabatically heated at the heliospheric termination shock. E. J. Zirnstein et al. only simulated and analyzed IBEX observations from the direction of Voyager 2. In this study, we expand our model to include fluxes from the direction of Voyager 1, as well as in the low-latitude part (middle) of the ribbon (10° below the ecliptic plane). We show that the model results at Voyager 1 are consistent with E. J. Zirnstein et al.'s results at Voyager 2 in terms of a secondary ENA source contribution of ≲20% from both directions. Our results in the middle of the ribbon also reproduce the data, when including a time-dependent secondary ENA source. Finally, we demonstrate with our simulation that three large pressure waves likely merged in the VLISM and were observed by Voyager 1 as "pf2," while at least one of the wave's effects in the HS was observed by IBEX as a brief enhancement in ENA flux in early 2016.

Keywords: Solar cycle, Heliosphere, Termination shock, Solar wind, Ion-neutral reactions, Heliosheath, Solar coronal mass ejections, Shocks
Machine-directed Gravitational-wave Counterpart Discovery. Joint observations in electromagnetic and gravitational waves shed light on the physics of objects and surrounding environments with extreme gravity that are otherwise unreachable via siloed observations in each messenger. However, such detections remain challenging due to the rapid and faint nature of counterparts. Protocols for discovery and inference still rely on human experts manually inspecting survey alert streams and intuiting optimal usage of limited follow-up resources. Strategizing an optimal follow-up program requires adaptive sequential decision-making given evolving light curve data that (i) maximizes a global objective despite incomplete information and (ii) is robust to stochasticity introduced by detectors/observing conditions. Reinforcement learning (RL) approaches allow agents to implicitly learn the physics or detector dynamics and the behavior policy that maximizes a designated objective through experience. To demonstrate the utility of such an approach for the kilonova follow-up problem, we train a toy RL agent with the goal of maximizing follow-up photometry for the true kilonova among several contaminant transient light curves. In a simulated environment where the agent learns online, it achieves 3× higher accuracy compared to a random strategy. However, it is surpassed by human agents by up to a factor of 2. This is likely because our hypothesis function (Q that is linear in state-action features) is an insufficient representation of the optimal behavior policy. More complex agents could perform at par or surpass human experts. Agents like these could pave the way for machine-directed software infrastructure to efficiently respond to next generation detectors, for conducting science inference and optimally planning expensive follow-up observations, scalably and with demonstrable performance guarantees.

Keywords: Surveys, Gravitational wave sources, Gravitational wave astronomy, Transient detection, Time domain astronomy
On the Dynamical Evolution of the Asteroid Belt in a Massive Star–Neutron Star Binary. Some fast radio bursts (FRBs) exhibit repetitive behaviors, and their origins remain enigmatic. It has been argued that repeating FRBs could be produced by the interaction between a neutron star and an asteroid belt. Here, we consider the systems in which an asteroid belt dwells around a massive star, while a neutron star, as a companion of the massive star, interacts with the belt through gravitational force. Various orbital configurations are assumed for the system. Direct N-body simulations are performed to investigate the dynamical evolution of the asteroids' belt. It is found that a larger orbital eccentricity of the neutron star will destroy the belt more quickly, with a large number of asteroids being scattered out of the system. A low inclination not only suppresses the collisions but also inhibits the ejection rate at early stages. However, highly inclined systems may undergo strong oscillations, resulting in the Kozai–Lidov instabilities. Among the various configurations, a clear periodicity is observed in the collision events for the case with an orbital eccentricity of 0.7 and mutual inclination of 0◦. It is found that such a periodicity can be sustained for at least eight neutron star orbital periods, supporting this mechanism as a possible explanation for periodically repeating FRBs. Our studies also suggest that the active stage of these kinds of FRB sources should be limited, since the asteroid belt would finally be destroyed by the neutron star after multiple passages.

Keywords: Radio continuum emission, Neutron stars, Radio bursts, Asteroids
Gaseous Dynamical Friction on Elliptical Keplerian Orbits. We compute the gaseous dynamical friction force experienced by massive perturbers on elliptical Keplerian orbits. Using linear perturbation theory, we investigate the density wake morphology, dynamical friction force, and secular orbital evolution for massive single perturbers as well as equal-mass binaries embedded in a homogeneous, static medium. In all cases, the rate of change in the semimajor axis is found to be negative (as expected), whereas the rate of change in eccentricity is negative for strictly subsonic trajectories and positive for strictly supersonic trajectories. Transonic orbits can experience both positive and negative torques during the course of an orbit, with some growing in eccentricity and others circularizing. We observe all initial orbits becoming highly supersonic and eccentric (over sufficiently long timescales) due to a relentless semimajor axis decay increasing the Mach number and subsequent eccentricity driving. We compare our findings to previous studies for rectilinear and circular motion while also making our data for the evolution of Keplerian orbits available.

Keywords: Elliptical orbits, Dynamical friction, Hydrodynamics