Sazuna/UAT_keywords huggingface dataset:
Forecasting Pulsar Timing Array Sensitivity to Anisotropy in the Stochastic Gravitational Wave Background. Statistical anisotropy in the nanohertz-frequency gravitational wave background (GWB) is expected to be detected by pulsar timing arrays (PTAs) in the near future. By developing a frequentist statistical framework that intrinsically restricts the GWB power to be positive, we establish scaling relations for multipole-dependent anisotropy decision thresholds that are a function of the noise properties, timing baselines, and cadences of the pulsars in a PTA. We verify that (i) a larger number of pulsars, and (ii) factors that lead to lower uncertainty on spatial cross-correlation measurements between pulsars, lead to a higher overall GWB signal-to-noise ratio, and lower anisotropy decision thresholds with which to reject the null hypothesis of isotropy. Using conservative simulations of realistic NANOGrav data sets, we predict that an anisotropic GWB with angular power C  l=1 &gt; 0.3C  l=0 may be sufficient to produce tension with isotropy at the p = 3 × 10-3 (~3σ) level in near-future NANOGrav data with a 20 yr baseline. We present ready-to-use scaling relationships that can map these thresholds to any number of pulsars, configuration of pulsar noise properties, or sky coverage. We discuss how PTAs can improve the detection prospects for anisotropy, as well as how our methods can be adapted for more versatile searches.

Keywords: Gravitational wave astronomy, Radio pulsars, Gravitational waves, Millisecond pulsars
Redshift-evolutionary X-Ray and UV Luminosity Relation of Quasars from Gaussian Copula. We construct a three-dimensional and redshift-evolutionary X-ray and ultraviolet (L  X -L  UV ) luminosity relation for quasars from the powerful statistic tool called copula, and find that the constructed L  X -L  UV  relation from copula is more viable than the standard one and the observations favor the redshift-evolutionary relation more than 3σ. The Akaike and Bayes information criterions indicate that the quasar data support strongly the three-dimensional L  X -L  UV  relation. Our results show that the quasars can be regarded as a reliable indicator of the cosmic distance if the L  X -L  UV  relation from copula is used to calibrate quasar data.

Keywords: Cosmology, Quasars
Effects of Inner Halo Angular Momentum on the Peanut/X Shapes of Bars. Cosmological simulations show that dark matter halos surrounding baryonic disks have a wide range of angular momenta, which is measured by the spin parameter (λ). In this study, we bring out the importance of inner angular momentum (&lt;30 kpc), measured in terms of the halo spin parameter, on the secular evolution of the bar using N-body simulations. We have varied the halo spin parameter λ from 0 to 0.1, for corotating (prograde) spinning halos and one counterrotating (retrograde) halo spin (λ = -0.1) with respect to the disk. We report that as the halo spin increases the buckling is also triggered earlier and is followed by a second buckling phase in high-spin halo models. The timescale for the second buckling is significantly longer than the first buckling. We find that bar strength does not reduce significantly after the buckling in all of our models, which provides new insights about the role of inner halo angular momentum unlike previous studies. Also, the buckled bar can still transfer significant angular momentum to the halo in the secular evolution phase, but it reduces with increasing halo spin. In the secular evolution phase, the bar strength increases and saturates to nearly equal values for all the models irrespective of halo spin and the sense of rotation with respect to the disk. The final boxy/peanut shape is more pronounced (~20%) in high-spin halos having higher angular momentum in the inner region compared to nonrotating halos. We explain our results with angular momentum exchanges between the disk and halo.

Keywords: Galaxy dark matter halos, Spiral galaxies, Galaxy structure, Galaxy kinematics, Galaxy evolution, N-body simulations
VERTICO. IV. Environmental Effects on the Gas Distribution and Star Formation Efficiency of Virgo Cluster Spirals. We measure the molecular-to-atomic gas ratio, R mol, and the star formation rate (SFR) per unit molecular gas mass, SFEmol, in 38 nearby galaxies selected from the Virgo Environment Traced in CO (VERTICO) survey. We stack ALMA 12CO (J = 2-1) spectra coherently using H I velocities from the VIVA survey to detect faint CO emission out to galactocentric radii r gal ~ 1.2 r 25. We determine the scale lengths for the molecular and stellar components, finding a ~3:5 relation compared to ~1:1 in field galaxies, indicating that the CO emission is more centrally concentrated than the stars. We compute R mol as a function of different physical quantities. While the spatially resolved R mol on average decreases with increasing radius, we find that the mean molecular-to-atomic gas ratio within the stellar effective radius R e , R mol(r &lt; R e ), shows a systematic increase with the level of H I, truncation and/or asymmetry (HI perturbation). Analysis of the molecular- and the atomic-to-stellar mass ratios within R e , ${R}_{\star }^{\mathrm{mol}}(r\lt {R}_{e})$ and ${R}_{\star }^{\mathrm{atom}}(r\lt {R}_{e})$ , shows that VERTICO galaxies have increasingly lower ${R}_{\star }^{\mathrm{atom}}(r\lt {R}_{e})$ for larger levels of HI perturbation (compared to field galaxies matched in stellar mass), but no significant change in ${R}_{\star }^{{\rm{m}}{\rm{o}}{\rm{l}}}(r\lt {R}_{e})$ . We also measure a clear systematic decrease of the SFEmol within R e , SFEmol(r &lt; Re ), with increasingly perturbed H I. Therefore, compared to field galaxies from the field, VERTICO galaxies are more compact in CO emission in relation to their stellar distribution, but increasingly perturbed atomic gas increases their R mol and decreases the efficiency with which their molecular gas forms stars.

Keywords: Galaxy clusters
Investigation of the Diamagnetic Drift Condition for the Suppression of Magnetic Reconnection in 3D Interlinked Reconnection Events with Magnetic Flux Pileup. We have performed a statistical survey to investigate possible diamagnetic drift suppression of magnetic reconnection using Magnetospheric Multiscale observations of interlinked magnetic field line events at Earth's magnetopause. Our goal is to investigate a possible cause for the observed magnetic field pileup on the two sides of the thin reconnecting current sheets, at the interface of the converging field lines. We compare whether the diamagnetic drift condition for the suppression of reconnection is satisfied before and after magnetic field pileup. We find that for a majority of events in our data set, the pre-pileup plasma β gradient and magnetic shear values were in the reconnection-suppressed regime, whereas the post-pileup values were in the reconnection-allowed regime. A possible interpretation is that reconnection was suppressed under the pre-pileup conditions, and this led to magnetic field pileup. The magnetic field pileup subsequently generated boundary conditions at the interlinked current sheet that overcame the diamagnetic drift suppression condition, allowing reconnection to happen in the interlinked field line structure. However, in one third of the events, the pre-pileup conditions were already in the reconnection-allowed regime, indicating that in such events, the diamagnetic suppression condition was probably not responsible for field pileup.

Keywords: Geomagnetic fields, Solar magnetic reconnection
Galactic Cosmic Rays at Mars and Venus: Temporal Variations from Hours to Decades Measured as the Background Signal of Onboard Microchannel Plates. A microchannel plate (MCP) is a component widely used for counting particles in space. Using the background counts from MCPs on the Mars Express and Venus Express orbiters-operating over 17 yr and 8 yr, respectively-we investigated the galactic cosmic ray (GCR) characteristics of the inner solar system. The MCP background counts at Mars and Venus, on a solar cycle timescale, exhibited clear anticorrelation with the sunspot number. We concluded that the measured MCP background counts contained GCR information. The GCR characteristics measured using the MCP background counts at Mars showed features consistent with measurements on Earth in Solar Cycle 24. The time lag between the sunspot number and the MCP background counts was found to be ~9 months at Mars. The shorter-term background data recorded along the orbits (with a timescale of several hours) also showed evident depletion of the background counts, due to absorption of the GCR particles by the planets. Thanks to the visible planetary size change along an orbit, we developed a model to separate the GCR contribution to the MCP background counts from the internal contribution caused by the β-decay of radioactive elements in the MCP glass. Our statistical analysis of the GCR absorption signatures at Mars implies that the effective absorption radius of Mars for the GCR particles is &gt;100 km larger than the radius of the planet. However, the cause remains an open question.

Keywords: Mars, Cosmic ray detectors, Venus, Planetary atmospheres, Galactic cosmic rays
Evidence of the Hall Effect Providing the Core Field inside a Magnetic Flux Rope in an Antiparallel Magnetic Reconnection. The observations from the Magnetospheric Multiscale mission on 2015 November 12 showed the existence of tripolar Hall magnetic fields north of the X line in a quasi-antiparallel reconnection at the dayside of the magnetopause. The bipolar variation in the normal component of the magnetic field inside the middle polar region of the tripolar Hall fields indicated the presence of an ion-scale magnetic flux rope. The coexistence of Hall fields and a magnetic flux rope provides the first evidence that the Hall effect in quasi-antiparallel magnetic reconnection can generate the core field inside a magnetic flux rope. There is one dip in the core field of the observed magnetic flux rope. We interpret the core field and the dip with the Hall effect associated with sequential multiple-X-line reconnection. The results of this study shed light on the mechanism of the generation of the core field inside the magnetic flux rope.

Keywords: Planetary magnetospheres, Solar wind
A New Method of Reconstructing Galactic 3D Structures Using Ultralong-wavelength Radio Observations. The free-free absorption of low-frequency radio waves by thermal electrons in the warm ionized medium of our Galaxy becomes very significant at ≲10 MHz (ultralong wavelength), and the absorption strength depends on the radio frequency. Upcoming space experiments such as the Discovering Sky at the Longest Wavelength and Farside Array for Radio Science Investigations of the Dark Ages and Exoplanets will produce high-resolution multifrequency sky maps at the ultralong wavelength, providing a new window to observe the universe. In this Paper we propose that from these ultralong-wavelength multifrequency maps, the 3D distribution of the Galactic electrons can be reconstructed. This novel and robust reconstruction of the Galactic electron distribution will be a key science case of those space missions. Ultralong-wavelength observations will be a powerful tool for studying the astrophysics relevant to the Galactic electron distribution, for example, the impacts of supernova explosions on electron distribution, and the interaction between interstellar atoms and ionizing photons escaped from the H II regions around massive stars.

Keywords: Interstellar plasma, Interstellar absorption, Interstellar medium, Radio interferometers, Milky Way Galaxy
Measuring He I Stark Line Shapes in the Laboratory to Examine Differences in Photometric and Spectroscopic DB White Dwarf Masses. Accurate helium White Dwarf (DB) masses are critical for understanding the star's evolution. DB masses derived from the spectroscopic and photometric methods are inconsistent. Photometric masses agree better with currently accepted DB evolutionary theories and are mostly consistent across a large range of surface temperatures. Spectroscopic masses rely on untested He I Stark line-shape and Van der Waals broadening predictions, show unexpected surface temperature trends, and are thus viewed as less reliable. To test this conclusion, we present in this paper detailed He I Stark line-shape measurements at conditions relevant to DB atmospheres (T electron ≈12,000-17,000 K, n electron ≈ 1017 cm-3). We use X-rays from Sandia National Laboratories' Z-machine to create a uniform ≈120 mm long hydrogen-helium mixture plasma. Van der Waals broadening is negligible at our experimental conditions, allowing us to measure He I Stark profiles only. Hβ, which has been well-studied in our platform and elsewhere, serves as the n e diagnostic. We find that He I Stark broadening models used in DB analyses are accurate within errors at tested conditions. It therefore seems unlikely that line-shape models are solely responsible for the observed spectroscopic mass trends. Our results should motivate the WD community to further scrutinize the validity of other spectroscopic and photometric input parameters, like atmospheric structure assumptions and convection corrections. These parameters can significantly change the derived DB mass. Identifying potential weaknesses in any input parameters could further our understanding of DBs, help elucidate their evolutionary origins, and strengthen confidence in both spectroscopic and photometric masses.

Keywords: DB stars, Plasma physics, Atomic physics, White dwarf stars, Laboratory astrophysics
Measuring the Ellipticity of M87* Images. The Event Horizon Telescope (EHT) images of the supermassive black hole at the center of the galaxy M87 provided the first image of the accretion environment on horizon scales. General relativity (GR) predicts that the image of the shadow should be nearly circular given the inclination angle of the black hole M87*. A robust detection of ellipticity in image reconstructions of M87* could signal new gravitational physics on horizon scales. Here we analyze whether the imaging parameters used in EHT analyses are sensitive to ring ellipticity, and measure the constraints on the ellipticity of M87*. We find that the top set is unable to recover ellipticity. Even for simple geometric models, the true ellipticity is biased low, preferring circular rings. Therefore, to place a constraint on the ellipticity of M87*, we measure the ellipticity of 550 synthetic data sets produced from GRMHD simulations. We find that images with intrinsic axis ratios of 2:1 are consistent with the ellipticity seen from EHT image reconstructions.

Keywords: Submillimeter astronomy, Black hole physics, Astronomy data analysis, Astronomy image processing
Spectropolarimetry as a Means to Address Cloud Composition and Habitability for a Cloudy Exoplanetary Atmosphere in the Habitable Zone. In our solar system, the densely cloud-covered atmosphere of Venus stands out as an example of how polarimetry can be used to gain information on cloud composition and particle mean radius. With current interest running high on discovering and characterizing extrasolar planets in the habitable zone where water exists in the liquid state, making use of spectropolarimetric measurements of directly imaged exoplanets could provide key information unobtainable through other means. In principle, spectropolarimetric measurements can determine if acidity causes water activities in the clouds to be too low for life. To this end, we show that a spectropolarimeter measurement over the range 400-1000 nm would need to resolve linear polarization to a precision of about 1% or better for reflected starlight from an optically thick cloud-enshrouded exoplanet. We assess the likelihood of achieving this goal by simulating measurements from a notional spectropolarimeter as part of a starshade configuration for a large space telescope (a HabEx design, but for a 6 m diameter primary mirror). Our simulations include consideration of noise from a variety of sources. We provide guidance on limits that would need to be levied on instrumental polarization to address the science issues we discuss. For photon-limited noise, integration times would need to be of order 1 hr for a large radius (10 Earth radii) planet to more than 100 hr for smaller exoplanets depending on the star-planet separation, planet radius, phase angle, and desired uncertainty. We discuss implications for surface chemistry and habitability.

Keywords: Exoplanet atmospheric composition , Occulting disks, Spectropolarimetry, Habitable planets
No Peaks without Valleys: The Stable Mass Transfer Channel for Gravitational-wave Sources in Light of the Neutron Star-Black Hole Mass Gap. Gravitational-wave (GW) detections are starting to reveal features in the mass distribution of double compact objects. The lower end of the black hole (BH) mass distribution is especially interesting as few formation channels contribute here and because it is more robust against variations in the cosmic star formation than the high-mass end. In this work we explore the stable mass transfer channel for the formation of GW sources with a focus on the low-mass end of the mass distribution. We conduct an extensive exploration of the uncertain physical processes that impact this channel. We note that, for fiducial assumptions, this channel reproduces the peak at ~9 M ☉ in the GW-observed binary BH mass distribution remarkably well and predicts a cutoff mass that coincides with the upper edge of the purported neutron star-black hole (NS-BH) mass gap. The peak and cutoff mass are a consequence of the unique properties of this channel; namely (1) the requirement of stability during the mass transfer phases, and (2) the complex way in which the final compact object masses scale with the initial mass. We provide an analytical expression for the cutoff in the primary component mass and show that this adequately matches our numerical results. Our results imply that selection effects resulting from the formation channel alone can provide an explanation for the purported NS-BH mass gap in GW detections. This provides an alternative to the commonly adopted view that the gap emerges during BH formation.

Keywords: Stellar mass black holes, Gravitational wave sources, Interacting binary stars, Supernova remnants, Gravitational waves
A Global Simulation of the Dynamo, Zonal Jets, and Vortices on Saturn. The fluid dynamics planet Saturn gives rise to alternating east-west jet streams, large cyclonic and anticyclonic vortices, and a dipole-dominant magnetic field that is highly axisymmetric about the planetary rotation axis. Modeling these features in a self-consistent manner is crucial for understanding the dynamics of Saturn's interior and atmosphere. Here we report a turbulent high-resolution dynamo simulation in a spherical shell that produces these features simultaneously for the first time. A crucial model ingredient is a long-hypothesized stably stratified layer (SSL), sandwiched between a deep metallic hydrogen layer and an outer low-conductivity molecular layer, born out of the limited solubility of helium inside metallic hydrogen at certain depths. The model spontaneously produces polar cyclones and significant low-latitude and midlatitude jet stream activity in the molecular layer. The off-equatorial low-latitude jet streams partially penetrate into the SSL and interact with the magnetic field. This helps to axisymmetrize the magnetic field about the rotation axis and convert some of the poloidal magnetic field to a toroidal field, which appears as two global magnetic energy rings surrounding the deeper dynamo region. The simulation also mimics a distinctive dip in the fifth spherical harmonic in Saturn's magnetic energy spectrum as inferred from the Cassini Grand Finale measurements. Our model highlights the role of an SSL in shaping the fluid dynamical and magnetic features of giant planets, as exemplified at Saturn.

Keywords: Magnetohydrodynamics, Saturn, Planetary atmospheres, Planetary science, Planetary interior, Magnetohydrodynamical simulations
The Jovian Energetic Ion Environment of Ganymede: Planetary Space Weather Considerations in View of the JUICE Mission. Determining the properties of radiation environments inside planetary magnetospheres is one of the key challenges of planetary space weather science. In this work, we expand our recent simulations of the Jovian energetic ion precipitation to Ganymede's surface to deduce ion circulation patterns at the altitude of ~500 km. We apply a single-particle Monte Carlo model to obtain 3D distribution maps of the H+, O++, and S+++ populations at the altitude of ~500 km. We perform these simulations for three distinct configurations between Ganymede's magnetic field and Jupiter's plasma sheet, characterized by magnetic and electric field conditions similar to those during the NASA Galileo G2, G8, and G28 flybys (i.e., when the moon was above, inside, and below the center of Jupiter's plasma sheet). Our results provide a reference frame for future studies of planetary space weather phenomena in the near-Ganymede region. For ions with energies up to some tens of kiloelectronvolts, we find an increased and spatially extended flow in the anti-Jupiter low-latitude and equatorial regions above Ganymede's leading hemisphere. Our results also show that the ion flux incident at 500 km altitude is not a good approximation of the surface's precipitating flux. To study, therefore, Ganymede's surface erosion processes it may be best to consider also low-altitude orbits as part of future space missions. This study is relevant to the ESA JUpiter ICy moons Explorer mission, which will allow a detailed investigation of the Ganymede environment and its implications on the moon's surface evolution.

Keywords: Ganymede
Formation and Reconnection of Electron Scale Current Layers in the Turbulent Outflows of a Primary Reconnection Site. We simulate with 3D particle in cell, the spontaneous formation of turbulent outflows in an initially laminar 3D reconnecting current layer. We observe the formation of many secondary current layers and reconnection sites in the outflow. The approach we follow is to study each individual feature within the turbulent outflow. To identify all clusters of current in the outflow we use a clustering technique widely used in unsupervised machine learning: density-based spatial clustering of applications with noise. Once the clusters are identified we measure their size and compute reconnection indicators to establish which are undergoing reconnection. With this analysis we establish that the size of the current clusters reaches all the way from its initial system scale down to subelectron skin depth scale. We observe that the smaller current clusters are more prone to reconnecting and to releasing energy. We then find the process of reconnection of the smaller current cluster to be of the recently observed electron-only type that leaves the ions essentially unaffected.

Keywords: Interplanetary turbulence, Solar magnetic reconnection
Dust Grains Cannot Grow to Millimeter Sizes in Protostellar Envelopes. A big question in the field of star and planet formation is the time at which substantial dust grain growth occurs. The observed properties of dust emission across different wavelength ranges have been used as an indication that millimeter-sized grains are already present in the envelopes of young protostars. However, this interpretation is in tension with results from coagulation simulations, which are not able to produce such large grains in these conditions. In this work, we show analytically that the production of millimeter-sized grains in protostellar envelopes is impossible under the standard assumptions about the coagulation process. We discuss several possibilities that may serve to explain the observed dust emission in the absence of in situ grain growth to millimeter sizes.

Keywords: Dust physics, Star forming regions, Planet formation