adsabs/SciX_UAT_keywords huggingface dataset:
Mass-to-light Ratios of Spatially Resolved Stellar Populations in M31

A galaxy's stellar mass-to-light ratio (M_{\star }/L) is a useful tool for converting luminosity to stellar mass (M_{\star }). However, the practical utility of M_{\star}/L inferred from stellar population synthesis (SPS) models is limited by mismatches between the real and assumed models for star-formation history (SFH) and dust geometry, both of which vary within galaxies. Here, we measure spatial variations in M_{\star}/L and their dependence on color, SFH, and dust across the disk of M31, using a map of M_{\star}CMD derived from color-magnitude diagrams of resolved stars in the Panchromatic Hubble Andromeda Treasury survey. First, we find comparable scatter in M_{\star}/L for the optical and mid-IR, contrary to the common idea that M_{\star }/L is less variable in the IR. Second, we confirm that M_{\star}/L is correlated with color for both the optical and mid-IR and report color versus M_{\star}/L relations (CMLRs) in M31 for filters used in the Sloan Digital Sky Survey and Widefield Infrared Survey Explorer. Third, we show that the CMLR residuals correlate with recent SFH, such that quiescent regions are offset to higher M_{\star}/L than star-forming regions at a fixed color. The mid-IR CMLR, however, is not linear due to the high scatter of M_{\star}/L in star-forming regions. Finally, we find a flatter optical CMLR than any SPS-based CMLRs in the literature. We show that this is an effect of dust geometry, which is typically neglected but should be accounted for when using optical data to map M_{\star}.

Keywords: galaxy masses; galaxy physics; andromeda galaxy; interstellar dust; star formation
Coevolution of Dust and Chemistry in Galaxy Simulations with a Resolved Interstellar Medium

Nearby dwarf irregular galaxies are ideal laboratories for studying the interstellar medium (ISM) at low metallicity, which is expected to be common for galaxies at very high redshift being observed by JWST. We present the first high-resolution (~0.2 pc) hydrodynamical simulations of an isolated low-metallicity (0.1 Z ⊙) dwarf galaxy coupled with a time-dependent chemistry network and a dust evolution model where dust is locally produced and destroyed by various processes. To accurately model carbon monoxide (CO), we post-process the simulations with a detailed chemistry network including the time-dependent effect of molecular hydrogen (H2). Our model successfully reproduces the observed star formation rate and CO(1-0) luminosity (L CO). We find that dust growth in dense gas is required to reproduce the observed L CO otherwise CO would be completely photodissociated. In contrast, the H2 abundance is extremely small and is insensitive to dust growth, leading to a CO-to-H2 conversion factor that is only slightly higher than the Milky Way value despite the low metallicity. An observationally inferred dust-to-gas ratio is thus underestimated if adopting the metallicity-dependent CO-to-H2 conversion factor. The newly produced dust in dense gas mixes with the ISM through supernova feedback without being completely destroyed by sputtering, which leads to galactic outflows 20%-50% dustier than the ISM, providing a possible source for intergalactic dust.

Keywords: interstellar medium; astrochemistry; hydrodynamical simulations
Bio-techno-signature Monitoring and Communication Guideposts for Extraterrestrial Life

Attendees at the First Penn State SETI Symposium collaborated to develop guideposts for monitoring for and communicating with extraterrestrial life. Over the course of six hours of moderated, dialogic, art-based inquiry in 2022 June, four foundational questions catalyzed the creation of a set of ethics-informed guideposts: Who speaks for Earth, and who should speak for Earth?; What can be communicated, and what is communicated?; What should be communicated?; and How can it be communicated? The 10 resulting parameters offer ethical navigation for examining bio- and techno-markers.

Keywords: detection; search for extraterrestrial intelligence
A Three-dimensional Map of the Heliosphere from IBEX

The Interstellar Boundary Explorer (IBEX) mission has shown that variations in the energetic neutral atom (ENA) flux from the outer heliosphere are associated with the solar cycle and longer-term variations in the solar wind (SW). In particular, there is a good correlation between the dynamic pressure of the outbound SW and variations in the later-observed IBEX ENA flux. The time difference between observations of the outbound SW and the heliospheric ENAs with which they correlate ranges from approximately 2 to 6 yr or more, depending on ENA energy and look direction. This time difference can be used as a means of "sounding" the heliosheath, that is, finding the average distance to the ENA source region in a particular direction. We apply this method to build a 3D map of the heliosphere. We use IBEX ENA data collected over a complete solar cycle, from 2009 through 2019, corrected for survival probability to the inner heliosphere. Here we divide the data into 56 "macropixels" covering the entire sky. As each point in the sky is sampled once every 6 months, this gives us a time series of 22 points macropixel-1 on which to time-correlate. Consistent with prior studies and heliospheric models, we find that the shortest distance to the heliopause, dHP, is slightly south of the nose direction (dHP ∼ 110-120 au), with a flaring toward the flanks and poles (dHP ∼ 160-180 au). The heliosphere extends at least ∼350 au tailward, which is the distance limit of the technique.

Keywords: heliosphere; heliopause; solar wind termination; heliosheath
Lunar Boulder Fields as Indicators of Recent Tectonic Activity

Wrinkle ridges are the predominant tectonic structure on the nearside lunar maria. Although lunar wrinkle ridge formation began as early as ∼3.9–4.0 Ga, recent investigations have identified wrinkle ridges in the lunar maria that were tectonically active as recently as the Copernican period of lunar geologic history. Some of those geologically young wrinkle ridges were identified by the presence of dense fields of meter-scale boulders on their scarps and topographic crests. Other investigations have identified recently active lunar wrinkle ridges that lack the ubiquitous presence of boulder fields, thereby rendering the presence of boulder fields ambiguous in the search for ongoing tectonic activity on the Moon. Here we assess boulder populations associated with 1116 wrinkle ridge segments on the lunar maria that are inferred to be recently active (<1.5 Ga) based on their crisp morphologies and crosscutting relationships with small impact craters. We utilize data from the Lunar Reconnaissance Orbiter Mini-RF and Diviner Lunar Radiometer Experiment instruments to assess surface rock populations across these recently active structures. Our results indicate that, where present, meter-scale boulder fields are likely indicators of fault-slip-induced ground acceleration given the short lifespan of lunar surface boulders. However, elevated boulder populations are not observed on all recently active ridges analyzed here. This latter observation supports the notion that wrinkle ridge boulder fields are a nonunique indicator of recent tectonic activity. Furthermore, the spatial distribution of those boulder fields indicates that variable mare protolith properties may play a role in boulder field formation.

Keywords: lunar evolution
Streaming Instability and Turbulence: Conditions for Planetesimal Formation

The streaming instability (SI) is a leading candidate for planetesimal formation, which can concentrate solids through two-way aerodynamic interactions with the gas. The resulting concentrations can become sufficiently dense to collapse under particle self-gravity, forming planetesimals. Previous studies have carried out large parameter surveys to establish the critical particle to gas surface density ratio (Z), above which SI-induced concentration triggers planetesimal formation. The threshold Z depends on the dimensionless stopping time (τ s , a proxy for dust size). However, these studies neglected both particle self-gravity and external turbulence. Here, we perform 3D stratified shearing box simulations with both particle self-gravity and turbulent forcing, which we characterize via a turbulent diffusion parameter, α D. We find that forced turbulence, at amplitudes plausibly present in some protoplanetary disks, can increase the threshold Z by up to an order of magnitude. For example, for τ s = 0.01, planetesimal formation occurs when Z ≳ 0.06, ≳0.1, and ≳0.2 at α D = 10‑4, 10‑3.5, and 10‑3, respectively. We provide a single fit to the critical Z required for the SI to work as a function of α D and τ s (although limited to the range τ s = 0.01–0.1). Our simulations also show that planetesimal formation requires a mid-plane particle-to-gas density ratio that exceeds unity, with the critical value being largely insensitive to α D. Finally, we provide an estimation of particle scale height that accounts for both particle feedback and external turbulence.

Keywords: planet formation; protoplanetary disks; hydrodynamics; hydrodynamical simulations; planetesimals
Entropy-conserving Scheme for Modeling Nonthermal Energies in Fluid Dynamics Simulations

We compare the performance of energy-based and entropy-conserving schemes for modeling nonthermal energy components, such as unresolved turbulence and cosmic rays, using idealized fluid dynamics tests and isolated galaxy simulations. While both methods are aimed to model advection and adiabatic compression or expansion of different energy components, the energy-based scheme numerically solves the nonconservative equation for the energy density evolution, while the entropy-conserving scheme uses a conservative equation for modified entropy. Using the standard shock tube and Zel'dovich pancake tests, we show that the energy-based scheme results in a spurious generation of nonthermal energy on shocks, while the entropy-conserving method evolves the energy adiabatically to machine precision. We also show that, in simulations of an isolated L ⋆ galaxy, switching between the schemes results in ≈20%-30% changes of the total star formation rate and a significant difference in morphology, particularly near the galaxy center. We also outline and test a simple method that can be used in conjunction with the entropy-conserving scheme to model the injection of nonthermal energies on shocks. Finally, we discuss how the entropy-conserving scheme can be used to capture the kinetic energy dissipated by numerical viscosity into the subgrid turbulent energy implicitly, without explicit source terms that require calibration and can be rather uncertain. Our results indicate that the entropy-conserving scheme is the preferred choice for modeling nonthermal energy components, a conclusion that is equally relevant for Eulerian and moving-mesh fluid dynamics codes.

Keywords: hydrodynamical simulations; galaxy evolution; stellar feedback; interstellar dynamics; cosmic rays; shocks
Drop in the Hard Pulsed Fraction and a Candidate Cyclotron Line in IGR J16320-4751 Seen by NuSTAR

We report on a timing and spectral analysis of a 50 ks NuSTAR observation of IGR J16320-4751 (= AX J1631.9-4752), a high-mass X-ray binary hosting a slowly rotating neutron star. In this observation from 2015, the spin period was 1308.8 ± 0.4 s giving a period derivative $\dot{P}\sim 2\times {10}^{-8}$ s s-1 when compared with the period measured in 2004. In addition, the pulsed fraction decreased as a function of energy, as opposed to the constant trend that was seen previously. This suggests a change in the accretion geometry of the system during the intervening 11 yr. The phase-averaged spectra were fit with the typical model for accreting pulsars: a power law with an exponential cutoff. This left positive residuals at 6.4 keV attributable to the known iron Kα line, as well as negative residuals around 14 keV from a candidate cyclotron line detected at a significance of 5σ. We found no significant differences in the spectral parameters across the spin period, other than the expected changes in flux and component normalizations. A flare lasting around 5 ks was captured during the first half of the observation, where the X-ray emission hardened and the local column density decreased. Finally, the binary orbital period was refined to 8.9912 ± 0.0078 days thanks to Swift/BAT monitoring data from 2005-2022.

Keywords: x-ray binary stars; high mass x-ray binary stars; neutron stars; pulsars; compact objects; massive stars
Chandra/LETGS Studies of the Collisional Plasma in 4U 1626-67

We present an analysis of Chandra/LETGS observations of the ultracompact X-ray binary (UCXB)4U 1626-67, continuing our project to analyze the existing Chandra gratings data of this interesting source. The extremely-low-mass, hydrogen-depleted donor star provides a unique opportunity to study the properties and structure of the metal-rich accreted plasma. There are strong, double-peaked emission features of O VII-VIII and Ne IX-X, but no other identified emission lines are detected. Our spectral fit simultaneously models the emission-line profiles and the plasma parameters, using a two-temperature collisionally-ionized plasma. Based on our line-profile fitting, we constrain the inclination of the system to 25-60° and the inner disk radius to ~1500 gravitational radii, in turn constraining the donor mass to ≲0.026 M⊙, while our plasma modeling confirms previous reports of high neon abundance in the source, establishing a Ne/O ratio in the system of 0.47 ± 0.04, while simultaneously estimating a very low Fe/O ratio of 0.0042 ± 0.0008 and limiting the Mg/O ratio to less than 1% by number. We discuss these results in light of previous work.

Keywords: neutron stars; stellar accretion disks; low-mass x-ray binary stars; high resolution spectroscopy; pulsars; compact binary stars; plasma astrophysics; white dwarf stars
The DESI Bright Galaxy Survey: Final Target Selection, Design, and Validation

Over the next 5 yr, the Dark Energy Spectroscopic Instrument (DESI) will use 10 spectrographs with 5000 fibers on the 4 m Mayall Telescope at Kitt Peak National Observatory to conduct the first Stage IV dark energy galaxy survey. At z < 0.6, the DESI Bright Galaxy Survey (BGS) will produce the most detailed map of the universe during the dark-energy-dominated epoch with redshifts of >10 million galaxies spanning 14,000 deg2. In this work, we present and validate the final BGS target selection and survey design. From the Legacy Surveys, BGS will target an r < 19.5 mag limited sample (BGS Bright), a fainter 19.5 < r < 20.175 color-selected sample (BGS Faint), and a smaller low-z quasar sample. BGS will observe these targets using exposure times scaled to achieve homogeneous completeness and cover the footprint three times. We use observations from the Survey Validation programs conducted prior to the main survey along with simulations to show that BGS can complete its strategy and make optimal use of "bright" time. BGS targets have stellar contamination <1%, and their densities do not depend strongly on imaging properties. BGS Bright will achieve >80% fiber assignment efficiency. Finally, BGS Bright and BGS Faint will achieve >95% redshift success over any observing condition. BGS meets the requirements for an extensive range of scientific applications. BGS will yield the most precise baryon acoustic oscillation and redshift-space distortion measurements at z < 0.4. It presents opportunities for new methods that require highly complete and dense samples (e.g., N-point statistics, multitracers). BGS further provides a powerful tool to study galaxy populations and the relations between galaxies and dark matter.

Keywords: observational cosmology; cosmology; redshift surveys; galaxies; galactic and extragalactic astronomy; galaxy spectroscopy; spectrophotometry
The 3D Distribution of Long-period Mira Variables in the Galactic Disk

Long-period Mira variable stars are considered to have relatively high initial masses and may be potentially useful as tracers of spiral arm structure of the Milky Way. From 2004 to 2017, we monitored long-period Mira candidates selected from the IRAS color-color diagram in the near-infrared K' band. As an initial result of this study, we found 108 Mira variables and determined their periods, mean magnitudes, and amplitudes. Most of them are located between 0° and 90° in Galactic longitude. The peak of their period distribution is at around 500 days, which is longer than the typical value for Mira variables selected in optical surveys. Distances to our Mira variables have also been estimated using the period-luminosity relation (PLR) in 3.4 μm with the help of a three-dimensional map of interstellar extinction. While the Ks-band PLR has a large scatter at longer periods (log P > 2.6), the PLR based on the Wide-field Infrared Survey Explorer 3.4 μm data has a much smaller scatter. We compare the spatial distribution of our sample to the spiral arms in the literature, and discuss the possible association of the long-period Mira variables with the spiral arms although the limited spatial coverage and the limited distance accuracy of the current sample prevent us from drawing a firm conclusion.

Keywords: milky way galaxy; asymptotic giant branch stars; distance indicators; spiral arms; mira variable stars
Forty Hypervelocity Stars from Gaia DR3

Forty hypervelocity stars (HVS) are detected from a search for HVS in Gaia DR3 data whose G magnitudes are less than 17.0 and radial velocities are more +400 km s‑1. The Gaia DR3 astrophysical parameters and spectra indicate that most of the HVS reported in this study are F, G, and K type metal-poor stars. Eleven stars are at high galactic latitudes. Included in this study are the B components of six nearby visual double stars BD-6 885B, HD 47503B, HD 53229B, HD 95123B, HD 180683B, and HD 202276B which are found to be HVS. The A components of these six visual doubles are less massive late-type stars with normal radial velocities. The source of hypervelocity of the B components is not clear. They may have less luminous and relatively massive degenerate component stars which are not yet detected. Further study of all these HVS is needed.

Keywords: hypervelocity stars
Investigating Orientation Effects Considering Angular Resolution for a Sample of Radio-loud Quasars Using VLA Observations

Radio core dominance measurements, an indicator of jet orientation, sometimes rely on core flux density measurements from large-area surveys like Faint Images of the Radio Sky at Twenty cm (FIRST) that have an angular resolution of only 5″. Such low-resolution surveys often fail to resolve cores from the extended emission, resulting in an erroneous measurement. We focus on investigating this resolution effect for a sample of 119 radio-loud quasars. We obtained continuum observations from NSF's Karl G. Jansky Very Large Array (VLA) at 10 GHz in A configuration with a 0"2 resolution. Our measurements show that at FIRST spatial resolution, core flux measurements are indeed systematically high even after considering the core variability. For a handful of quasars, 10 GHz images reveal extended features, whereas the FIRST image shows a point source. We found that the resolution effect is more prominent for quasars with smaller angular sizes. We further computed two radio core dominance parameters R and R5100 for use in statistical orientation investigations with this sample. We also present the spectral energy distributions between 74 MHz and 1.4 GHz, which we used to measure the spectral index of the extended emission of these quasars. Our results empirically confirm that determination of radio core dominance requires high spatial resolution data. We highlight the practical issues associated with the choice of frequency and resolution in the measurement of core and extended flux densities.

Keywords: quasars; radio loud quasars; very large array; active galactic nuclei; radio cores
Scientific Impact of Novel Instrumentation: The Case of MUSE

In the process of transforming science cases into a viable and affordable design for a novel instrument, there is the problem of how to gauge their scientific impact, especially when they end up in competing top level requirements that can be incompatible with each other. This research note presents a case study for scientific impact of the integral field spectrograph MUSE in terms of number of refereed publications from 2014 to 2024 as a figure of merit, broken down by different research areas. The analysis is based on the Basic ESO Publication Statistics service and NASA's Astrophysics Data System.

Keywords: astronomical instrumentation
Magnetic Imprints of Eruptive and Noneruptive Solar Flares as Observed by Solar Dynamics Observatory

The abrupt and permanent changes of the photospheric magnetic field in the localized regions of active regions during solar flares, called magnetic imprints (MIs), have been observed for nearly the past three decades. The well-known coronal implosion model is assumed to explain such flare-associated changes but the complete physical understanding is still missing and debatable. In this study, we made a systematic analysis of flare-related changes of the photospheric magnetic field during 21 flares (14 eruptive and seven noneruptive) using the 135 s cadence vector magnetogram data obtained from the Helioseismic and Magnetic Imager. The MI regions for eruptive flares are found to be strongly localized, whereas the majority of noneruptive events (>70%) have scattered imprint regions. To quantify the strength of the MIs, we derived the integrated change of horizontal field and the total change of Lorentz force over an area. These quantities correlate well with the flare strength, irrespective of whether flares are eruptive or not, or have a short or long duration. Further, the free energy (FE), determined from virial theorem estimates, exhibits a statistically significant downward trend that starts around the flare time and is observed in the majority of flares. The change of FE during flares does not depend on eruptivity but has a strong positive correlation (≈0.8) with the Lorentz force change, indicating that part of the FE released would penetrate the photosphere. While these results strongly favor the idea of significant feedback from the corona on the photospheric magnetic field, the characteristics of MIs are quite indistinguishable from flares being eruptive or not.

Keywords: solar activity; solar photosphere; solar flares; solar coronal mass ejections