Sazuna/UAT_keywords huggingface dataset:
Quantifying the Impact of the Dust Torque on the Migration of Low-mass Planets. II. The Role of Pebble Accretion in Planet Growth within a Global Planet Formation Model. Although dust constitutes only about 1% of the mass in a protoplanetary disk, recent studies reveal its substantial impact on the torques experienced by low- and intermediate-mass planetary cores. In this study, we present the first comprehensive analysis of the dust torque's influence on the evolution of growing planetary embryos as they migrate through a protoplanetary disk and undergo gas and pebble accretion. Our global model incorporates viscous accretion and X-ray photoevaporation effects on the gaseous disk while also accounting for the dynamic processes of dust growth and evolution, including coagulation, drift, and fragmentation. Our findings demonstrate that dust torque significantly affects planetary migration patterns, particularly facilitating prominent outward migration for planets forming within the water-ice line. This outward thrust arises from an enhanced dust-to-gas mass ratio in the inner disk, driven by the inward drift of pebbles from the outer regions. Conversely, for planets that originate beyond the water-ice line, while the dust torque attenuates inward migration, it does not substantially alter their overall migration trajectories. This is attributed to the rapid reduction in dust-to-gas mass ratio, resulting from swift pebble drift and the short formation timescales prevalent in that region. Overall, our findings highlight the critical role of dust torque in shaping the migration of low- and intermediate-mass planets, particularly in conditions where increased dust concentrations amplify its effects. These insights have significant implications for understanding the formation timescales, mass distributions, and compositional characteristics of emerging planetary systems.

Keywords: Exoplanet migration, Planetary-disk interactions, Protoplanetary disks, Planetary migration, Planet formation
Detection of Hydrocarbons in the Disk around an Actively Accreting Planetary-mass Object. We present the 0.6–12 μm spectrum of Cha 1107-7626, a 6–10 Jupiter-mass free-floating object in the ∼2 Myr-old Chamaeleon-I star-forming region, from observations with the NIRSpec and MIRI instruments on board the James Webb Space Telescope. We confirm that Cha 1107-7626 is one of the lowest-mass objects known to harbor a dusty disk with infrared excess emission at wavelengths beyond 4 μm. Our NIRSpec data and prior ground-based observations provide strong evidence for ongoing accretion through hydrogen recombination lines. In the mid-infrared spectrum, we detect unambiguously emission lines caused by methane (CH4) and ethylene (C2H4) in its circumsubstellar disk. Our findings mean that Cha 1107-7626 is by far the lowest-mass object with hydrocarbons observed in its disk. The spectrum of the disk looks remarkably similar to that of ISO-ChaI 147, a very low-mass star with a carbon-rich disk that is 10–20 times more massive than Cha 1107-7626. The hydrocarbon lines can be accounted for with a model assuming gas temperatures of a few hundred kelvin in the inner disk. The obvious similarities between the spectra of a low-mass star and a planetary-mass object indicate that the conditions in the inner disks can be similar across a wide range of central object masses.

Keywords: Brown dwarfs, Infrared spectroscopy, Free floating planets, Protoplanetary disks, Stellar accretion, Stellar accretion disks
Describing the Nonuniversal Galaxy Merger Timescales in IllustrisTNG: Effects of Host Halo Mass, Baryons, and Sample Selection. Galaxy merger timescales are crucial for understanding and modeling galaxy formation in our hierarchically structured Universe. However, previous studies have reported widely varying dependencies of merger timescales on initial orbital parameters and mass ratios at the first crossing of rvir. Using IllustrisTNG simulations, we find that these dependencies vary with host halo mass, suggesting that discrepancies in prior studies may arise from differences in the systems analyzed. Specifically, in low-mass halos, merger timescales show a stronger dependence on initial orbital parameters, while, in high-mass halos, this dependence weakens. To account for these variations, we present a fitting formula that incorporates host mass dependence, achieving a logarithmic scatter smaller than 0.15 dex. Comparing dark-matter-only and baryonic simulations, we observe similar merger timescales for circular orbits but notable differences for radial orbits. In halos with Mhost &lt; 1012.5h‑1M⊙, mergers in dark-matter-only runs take longer than in baryonic runs, whereas the trend reverses in more massive halos. We attribute these differences to the competing effects of tidal disruption by central galaxy disks and the resistance of baryonic satellites to tidal stripping. Finally, we extend our model to predict merger timescales from any starting radius within the halo. By fitting the extended model to the entire infall sample, we find that using only the merger sample can underestimate merger timescales, particularly for low mass ratios. Our model provides a valuable tool for improving semianalytical and empirical models of galaxy formation.

Keywords: Hydrodynamical simulations, Galaxy mergers, Dynamical friction, Galaxy evolution
Results from an Einstein@Home Search for Continuous Gravitational Waves from Cassiopeia A and Vela Jr. Using LIGO O2 Data. We conduct two searches for continuous, nearly monochromatic gravitational waves originating from the central compact objects in the supernova remnants Cassiopeia A (Cas A) and Vela Jr. using public LIGO data. The search for Cas A targets signal frequencies between 20 Hz and 400 Hz, and the Vela Jr. search covers between 400 and 1700 Hz. They both investigate the broadest set of waveforms ever considered with highly sensitive deterministic search methods. Above 1500 Hz, the Vela Jr. search is the most sensitive carried out thus far, improving on previous results by over 300%. Above 976 Hz these results improve on existing ones by 50%. In all, we investigate over 1018 waveforms, leveraging the computational power donated by thousands of Einstein@Home volunteers. We perform a four-stage follow-up on more than 6 million waveforms. None of the considered waveforms survives the follow-up scrutiny, indicating no significant detection candidate. Our null results constrain the maximum amplitude of continuous signals as a function of signal frequency from the targets. The most stringent 90% confidence upper limit for Cas A is  h090%≈7.3×10‑26  near 200 Hz, and for Vela Jr. it is  h090%≈8.9×10‑26  near 400 Hz. Translated into upper limits on the ellipticity and r-mode amplitude, our results probe physically interesting regions: for example, the ellipticity of Vela Jr. is constrained to be smaller than 10‑7 across the frequency band, with a tighter constraint of less than 2 × 10‑8 at the highest frequencies.

Keywords: Supernova remnants, Neutron stars, Gravitational waves
Linear Response of Rotating and Flattened Stellar Clusters: The Oblate Kuzmin─Kutuzov Stäckel Family. This paper investigates the linear response of a series of spheroidal stellar clusters, the Kuzmin─Kutuzov Stäackel family, which exhibit a continuous range of flattening and rotation, extending from an isochrone sphere to a Toomre disk. The method successfully replicates the growing modes previously identified in published N-body simulations. It relies on the efficiency of the matrix method to quantify systematically the effects of rotation and flattening on the eigenmodes of the galaxy. We identify two types of bisymmetric instabilities for the flatter models—the so-called bending and bar-growing modes—the latter of which persists even for very round models. As anticipated, in its least unstable configurations, the system becomes flatter as its rotational speed increases. More realistic equilibria will be required to achieve a better match to the main sequence of fast─slow rotators. The corresponding code is made public.

Keywords: Gravitation, Galaxy dynamics, Galaxy kinematics, Stellar diffusion
Clouds Can Enhance Direct-imaging Detection of O<SUB>2</SUB> and O<SUB>3</SUB> on Terrestrial Exoplanets. Clouds are often considered a highly uncertain barrier for detecting biosignatures on exoplanets, especially given intuition gained from transit surveys. However, for direct-imaging reflected light observations, clouds could increase the observational signal by increasing reflected light. Here we constrain the impact of clouds on the detection of O2 and O3 by a direct-imaging telescope such as the Habitable Worlds Observatory (HWO) using observations simulated with the Planetary Spectrum Generator (PSG). We first perform sensitivity tests to show that low clouds enhance O2 and O3 detectability while high clouds diminish it, and the effect is greater when cloud particles are smaller. We next apply clouds produced by the cloud microphysics model Community Aerosol and Radiation Model for Atmospheres with varied planetary parameters and clouds drawn from observations of different types of clouds on Earth to PSG. We find that clouds are likely to increase the signal-to-noise ratio of O2 and O3 for terrestrial exoplanets under a wide range of scenarios. This work provides important constraints on the impact of clouds on observations by telescopes including HWO.

Keywords: Biosignatures, Exoplanet atmospheres, Direct imaging, Atmospheric clouds
Formation of H<SUP>+</SUP> PUI Tails Downstream of Distant Interplanetary Shocks. New Horizons' Solar Wind Around Pluto (SWAP) instrument has observed interplanetary shocks from ∼20 to 60 au from the Sun. Different studies have analyzed the effects of these shocks on the solar wind ion (SWI) and interstellar pickup ion (PUI) distributions. A key finding includes the observation of PUI tails downstream of some shocks. However, PUI tails have only been observed when SWAP was measuring 24 hr averages of the count rate histograms. After a software change in 2021 February, SWAP's measurement resolution was improved to ∼30 minutes averages, but no PUI tails have been observed since this change. In this study, we use a test particle code to simulate the downstream SWI and PUI distributions to study the possible existence and formation of PUI tails, using the shock compression ratio, shock thickness, and turbulence as free parameters. We find that in most cases, a suprathermal tail does not develop downstream of interplanetary shocks, but a persistent hump and PUI cutoff exists at energies above the PUI injection energy. The extent of the hump largely depends on the shock compression ratio. We find PUI tails do form when turbulence is included in the model. After we convert our distributions to count rates in the spacecraft frame, the results show similar structure to the data. We conclude that significant H+ PUI tails can form downstream of distant interplanetary shocks if there is a relatively large compression ratio (&gt;2) and significant turbulence present.

Keywords: Interplanetary shocks, Heliosphere, Interplanetary turbulence, Solar wind, Particle physics
Modern Earth-like Chemical Disequilibrium Biosignatures are Challenging to Constrain through Spectroscopic Retrievals. Robust exoplanet characterization studies are underway, and the community is looking ahead toward developing observational strategies to search for life beyond our solar system. With the development of life detection approaches like searching for atmospheric chemical species indicative of life, chemical disequilibrium has also been proposed as a potentially key signature for life. Chemical disequilibrium can arise from the production of waste gases due to biological processes and can be quantified using a metric known as the available Gibbs free energy. The main goal of this study was to explore the detectability of chemical disequilibrium for a modern Earth-like analog. Atmospheric retrievals coupled to a thermodynamics model were used to determine posterior distributions for the available Gibbs free energy given simulated observations at various noise levels. In reflected light, chemical disequilibrium signals were difficult to detect and limited by the constraints on the CH4 abundance, which was challenging to constrain for a modern Earth case with simulated observations spanning ultraviolet through near-infrared wavelengths with V band signal-to-noise ratios of 10, 20, and 40. For a modern Earth analog orbiting a late-type M dwarf, we simulated transit observations with the James Webb Space Telescope Mid-Infrared Instrument and found that tight constraints on the available Gibbs free energy can be achieved, but only at extremely low noise on the order of several parts per million. This study serves as further proof of concept for remotely inferring chemical disequilibrium biosignatures and should be included in continuing to build life detection strategies for future exoplanet characterization missions.

Keywords: Astrobiology
X-Ray Polarization Study of the Neutron Star Low-mass X-Ray Binary GX 349+2. We report the first X-ray polarimetric results of the neutron star (NS) low-mass X-ray binary Z-source GX 349+2 using the Imaging X-ray Polarimetry Explorer (IXPE). We discovered that the X-ray source was polarized at a polarization degree of PD = 1.1% ± 0.3% (1σ errors) with a polarization angle of PA = 32° ± 6° (1σ errors). Simultaneous Nuclear Spectroscopic Telescope Array observations show that the source transitioned through the normal branch, flaring branch, and soft apex of the Z-track during our IXPE observations. The X-ray spectropolarimetry results suggest a source geometry comprising an accretion disk component, a blackbody representing the emission from the NS surface, and a Comptonized component. We discuss the accretion geometry of the Z-source in light of the spectropolarimetric results.

Keywords: Accretion, Neutron stars, X-ray binary stars, Low-mass x-ray binary stars, Polarimetry
Intermediate Mass Ratio Inspirals in Milky Way Galaxies. A consequence of a nonzero occupation fraction of massive black holes (MBHs) in dwarf galaxies is that these MBHs can become residents of larger galaxy halos via hierarchical merging and tidal stripping. Depending on the parameters of their orbits and original hosts, some of these MBHs will merge with the central supermassive black hole in the larger galaxy. We examine four cosmological zoom-in simulations of Milky Way-like galaxies to study the demographics of the black hole mergers that originate from dwarf galaxies. Approximately half of these mergers have mass ratios less than 0.04, which we categorize as intermediate mass ratio inspirals, or IMRIs. Inspiral durations range from 0.5─8 Gyr, depending on the compactness of the dwarf galaxy. Approximately half of the inspirals may become more circular with time, while the eccentricity of the remainder does not evolve. Overall, IMRIs in Milky Way-like galaxies are a significant class of black hole mergers that can be detected by LISA, and must be prioritized for waveform modeling.

Keywords: Black hole physics, Galaxy formation, Intermediate-mass black holes, Gravitational waves
Parker Solar Probe Observations of a Highly Energetic and Asymmetric Reconnecting Heliospheric Current Sheet during Encounter 13. We report Parker Solar Probe observations of reconnection during an unusual heliospheric current sheet (HCS) crossing at 14.8 solar radii that occurred ∼15 hr after the passage of a CME. The HCS was surrounded by unusually low solar wind density. The hybrid Alfvén speed (VA ∼ 515 km s−1) and available magnetic energy per particle (miVA2 ∼ 3 keV) were the highest observed to date surrounding an HCS. Inside the HCS, the peak outflow speed (∼525 km s−1) and proton and electron bulk heating, at ∼400 eV and ∼25 eV, respectively, were also the highest observed to date associated with HCS reconnection. Unusual for an HCS, the density on the two sides of the HCS differed by a factor of ∼13. Consequently, the spatial plasma profiles across the HCS resembled those of planetary magnetopauses, with the fastest outflow occurring near the low-density edge of the HCS. A striking feature of this HCS is the asymmetric nature of the superthermal protons escaping the HCS along separatrix field lines. On the low solar wind density side, the low-velocity cutoff of escaping protons was substantially higher than on the high-density side. The cutoffs were close to the bulk outflow speeds measured near the two edges of the asymmetric HCS, suggesting that only particles faster than the outflow speeds can escape the HCS. Electrons were also energized and leaked out of the HCS, forming a layer of field-aligned superthermal electrons. These escaping electrons are distinguishable from solar strahl electrons observed further away from the HCS, which had lower energies.

Keywords: Solar physics, Solar wind, Solar magnetic reconnection
X-Ray Polarization in SN 1006 Southwest Shows Spatial Variations and Differences in the Radio Band. We report the detection of a spatial variation of X-ray polarization in the southwestern (SW) shell of supernova remnant SN 1006 (SN 1006 SW) using the Imaging X-ray Polarimetry Explorer (IXPE). The shell has an average X-ray polarization degree (PD) of 21.6% ± 4.5% and polarization angle of −48∘ ± 5∘ in the 2─4 keV energy band, similar to those in the northeastern shell. The PD varies along SN 1006 SW, with a peak PD = 40% ± 8% in the south and a significantly lower PD ≲ 27% (99% upper limit) in the west, where the shell has been proposed to be interacting with an interstellar cloud. The correlation between the PD, which reflects the magnetic orderliness, and the preshock density provides observational evidence that magnetic turbulence and amplification are environment-dependent. The high PD detected in the southern region of the shell constrains the magnetic turbulence scale to ≲0.1 pc. Moreover, by comparing the IXPE X-ray and MeerKAT radio polarization measurements for SN 1006 SW, we found that magnetic fields traced by X-ray polarization are nearly radially distributed, whereas those traced by radio polarization tend to follow a direction parallel to the Galactic plane. This suggests that the X-ray polarization probes freshly amplified magnetic fields from small-scale structures in the immediate postshock region, while the radio traces more extended regions influenced by the preexisting ambient magnetic fields.

Keywords: Magnetic fields, Supernova remnants, Shocks, Polarimetry, Cosmic rays
Generation of Large-scale Magnetic Fields Upstream of Gamma-Ray Burst Afterglow Shocks. The origins of the magnetic fields that power gamma-ray burst (GRB) afterglow emission are not fully understood. One possible channel for generating these fields involves the pre-conditioning of the circumburst medium: in the early afterglow phase, prompt photons streaming ahead of the GRB external shock can pair produce, seeding the upstream with drifting electron─positron pairs and triggering electromagnetic microinstabilities. To study this process, we employ 2D periodic particle-in-cell simulations in which a cold electron─proton plasma is gradually enriched with warm electron─positron pairs injected at mildly relativistic speeds. We find that continuous pair injection drives the growth of large-scale magnetic fields via filamentation-like instabilities; the temporal evolution of the field is self-similar and depends on a single parameter,  α/(tfωpi)1/2tωpi , where α is the ratio of final pair beam density to background plasma density, tf is the duration of pair injection, and ωpi is the plasma frequency of background protons. Extrapolating our results to parameter regimes realistic for long GRBs, we find that upstream pair enrichment generates weak magnetic fields on scales much larger than the proton skin depth; for bright bursts, the extrapolated coherence scale at a shock radius of R ∼ 1017 cm is  λy∼100c/ωpi , and the corresponding magnetization is σ ∼ 10−8 for typical circumburst parameters. These results may help explain the persistence of magnetic fields at large distances behind GRB shocks.

Keywords: Shocks, Gamma-ray bursts, Plasma astrophysics, High energy astrophysics
Spatially Resolved Galaxy─Dust Modeling with Coupled Data-driven Priors. A notorious problem in astronomy is the recovery of the true shape and spectral energy distribution (SED) of a galaxy despite attenuation by interstellar dust embedded in the same galaxy. This problem has been solved for a few hundred nearby galaxies with exquisite data coverage, but these techniques are not scalable to the billions of galaxies soon to be observed by large wide-field surveys like the Legacy Survey of Space and Time, Euclid, and Roman. We present a method for jointly modeling the spatially resolved stellar and dust properties of galaxies from multiband images. To capture the diverse geometries of galaxies, we consider nonparametric morphologies, stabilized by two neural networks that act as data-driven priors: the first informs our inference of the galaxy's underlying morphology, while the second constrains the galaxy's dust morphology conditioned on our current estimate of the galaxy morphology. We demonstrate with realistic simulations of z ∼ 0 galaxies that we can recover galaxy host and dust properties over a wide range of attenuation levels and geometries. We apply our joint galaxy─dust model to three local galaxies observed by the Sloan Digital Sky Survey and find qualitatively good results. In addition to improving estimates of unattenuated galaxy SEDs, our inferred dust maps will facilitate the study of dust production, transport, and destruction. However, without informed priors on the inferred host spectrum, our method is vulnerable to the thin-screen limit; future work will need to address this degeneracy with stellar population synthesis modeling.

Keywords: Extragalactic astronomy, Interstellar dust extinction, Neural networks
On Acceleration of Highest-energy Cosmic Rays in a Novel Scenario of Magnetar Transients. Transient phenomena in magnetars have been considered as possible acceleration sites of ultra-high-energy cosmic rays (CRs), whose energy reaches ∼200 EeV, such as the Amaterasu particle. However, the process of CR acceleration and the trigger mechanism of magnetar transients remain unclear. A recently suggested scenario for the activity predicts that the magnetar's rotation axis suddenly flips due to the "Dzhanibekov effect," resulting in a sudden rise of the Euler force. The material in the outer layer plastically flows due to the force and finally fractures in this scenario. We study the possibilities of ion acceleration along with this scenario. If the degenerate electrons burst open from the fractured region like a balloon burst, the pair plasma formation can be ignited inside the crust. We find that such pair plasma can emit photons similar to the observed bursts from magnetars. We also find that the electron stream at the beginning of the burst phenomenon possibly induces a strong electric field for a moment, resulting in the acceleration of ∼1 ZeV ion within a timescale of ∼1 ps. The nuclear spallation reactions limit this timescale, and therefore, high-energy CR "neutrons" from the parenteral nuclei become proper observational predictions of this scenario: their arrival time and direction will be correlated with the bursting photon emissions of the host magnetars. The nuclear spallation of ∼1 ZeV nuclei is preferred to explain ≳10 PeV neutrino events observed by IceCube and KM3Net.

Keywords: Solid matter physics, Neutrino astronomy, Cosmic ray astronomy, X-ray transient sources, Particle astrophysics, Cosmic rays