adsabs/SciX_UAT_keywords huggingface dataset:
Two Ultra-faint Milky Way Stellar Systems Discovered in Early Data from the DECam Local Volume Exploration Survey

We report the discovery of two ultra-faint stellar systems found in early data from the DECam Local Volume Exploration survey (DELVE). The first system, Centaurus I (DELVE J1238-4054), is identified as a resolved overdensity of old and metal-poor stars with a heliocentric distance of ${\text{}}{D}_{\odot }={116.3}_{-0.6}^{+0.6}\,\mathrm{kpc}$ , a half-light radius of ${r}_{h}={2.3}_{-0.3}^{+0.4}\,\mathrm{arcmin}$ , an age of $\tau \gt 12.85\,\mathrm{Gyr}$ , a metallicity of $Z={0.0002}_{-0.0002}^{+0.0001}$ , and an absolute magnitude of ${M}_{V}=-{5.55}_{-0.11}^{+0.11}\,\mathrm{mag}$ . This characterization is consistent with the population of ultra-faint satellites and confirmation of this system would make Centaurus I one of the brightest recently discovered ultra-faint dwarf galaxies. Centaurus I is detected in Gaia DR2 with a clear and distinct proper motion signal, confirming that it is a real association of stars distinct from the Milky Way foreground; this is further supported by the clustering of blue horizontal branch stars near the centroid of the system. The second system, DELVE 1 (DELVE J1630-0058), is identified as a resolved overdensity of stars with a heliocentric distance of ${\text{}}{D}_{\odot }={19.0}_{-0.6}^{+0.5}\,\mathrm{kpc}$ , a half-light radius of ${r}_{h}={0.97}_{-0.17}^{+0.24}\,\mathrm{arcmin}$ , an age of $\tau ={12.5}_{-0.7}^{+1.0}\,\mathrm{Gyr}$ , a metallicity of $Z={0.0005}_{-0.0001}^{+0.0002}$ , and an absolute magnitude of ${M}_{V}=-{0.2}_{-0.6}^{+0.8}\,\mathrm{mag}$ , consistent with the known population of faint halo star clusters. Given the low number of probable member stars at magnitudes accessible with Gaia DR2, a proper motion signal for DELVE 1 is only marginally detected. We compare the spatial position and proper motion of both Centaurus I and DELVE 1 with simulations of the accreted satellite population of the Large Magellanic Cloud (LMC) and find that neither is likely to be associated with the LMC.

Keywords: dwarf galaxies; local group; star clusters; milky way galaxy
Milky Way Satellite Census. IV. Constraints on Decaying Dark Matter from Observations of Milky Way Satellite Galaxies

We use a recent census of the Milky Way (MW) satellite galaxy population to constrain the lifetime of particle dark matter (DM). We consider two-body decaying dark matter (DDM) in which a heavy DM particle decays with lifetime τ comparable to the age of the universe to a lighter DM particle (with mass splitting ϵ) and to a dark radiation species. These decays impart a characteristic "kick velocity," V kick = ϵ c, on the DM daughter particles, significantly depleting the DM content of low-mass subhalos and making them more susceptible to tidal disruption. We fit the suppression of the present-day DDM subhalo mass function (SHMF) as a function of τ and V kick using a suite of high-resolution zoom-in simulations of MW-mass halos, and we validate this model on new DDM simulations of systems specifically chosen to resemble the MW. We implement our DDM SHMF predictions in a forward model that incorporates inhomogeneities in the spatial distribution and detectability of MW satellites and uncertainties in the mapping between galaxies and DM halos, the properties of the MW system, and the disruption of subhalos by the MW disk using an empirical model for the galaxy-halo connection. By comparing to the observed MW satellite population, we conservatively exclude DDM models with τ < 18 Gyr (29 Gyr) for V kick = 20 kms-1 (40 kms-1) at 95% confidence. These constraints are among the most stringent and robust small-scale structure limits on the DM particle lifetime and strongly disfavor DDM models that have been proposed to alleviate the Hubble and S 8 tensions.

Keywords: dark matter; milky way dark matter halo; galaxy abundances
Harnessing Unresolved Lensed Quasars: The Mathematical Foundation of the Fluctuation Curve

Strong gravitational lensed quasars (QSOs) have emerged as powerful and novel cosmic probes as they can deliver crucial cosmological information, such as a measurement of the Hubble constant, independent of other probes. Although the upcoming LSST survey is expected to discover 103-104 lensed QSOs, a large fraction will remain unresolved due to seeing. The stochastic nature of the quasar intrinsic flux makes it challenging to identify lensed quasars and measure the time delays using unresolved light-curve data only. In this regard, Bag et al. introduced a data-driven technique based on the minimization of the fluctuation in the reconstructed image light curves. In this article, we delve deeper into the mathematical foundation of this approach. We show that the lensing signal in the fluctuation curve is dominated by the autocorrelation function (ACF) of the derivative of the joint light curve. This explains why the fluctuation curve enables the detection of the lensed QSOs only using the joint light curve, without making assumptions about QSO flux variability, nor requiring any additional information. We show that the ACF of the derivative of the joint light curve is more reliable than the ACF of the joint light curve itself because intrinsic quasar flux variability shows significant autocorrelation up to a few hundred days (as they follow a red power spectrum). In addition, we show that the minimization of fluctuation approach provides even better precision and recall as compared to the ACF of the derivative of the joint light curve when the data have significant observational noise.

Keywords: quasars; strong gravitational lensing; astrostatistics techniques
The Importance of Hall Effect in the Self-similar Collapse of a Filamentary Cloud

Thanks to the observational and simulation works, the importance of the nonideal magnetohydrodynamic (MHD) effects, i.e., Hall effect, ohmic resistivity, and ambipolar diffusion, have been well established at various stages of cloud evolution. To get a comparison between the Hall effect with other effects, we aim to model the time evolution of a rotating filamentary molecular cloud during the isothermal/polytropic collapse phase in the presence of the Hall drift. Three components of the velocity vector are investigated when the angular momentum is fully coupled with the magnetic field at large radii of a filament. For this purpose, the nonideal MHD equations in the self-similar formalism are considered at large radii of a molecular cloud where the magnetic field evolution is affected by the Hall drift. Then, the connection between the self-similar approach with the observational data from the filamentary clouds is examined to get a realistic model. Due to the existence of Hall drift, the significant changes on the rotation of the cloud can be seen when the cloud switches from the isothermal collapse phase to the polytropic collapse phase. Also, the results of this model are useful in the study of the multiple star formation process as well as the initial conditions for driving the outflows during the collapse of the filamentary clouds. Finally, we found that there are some conditions for the comparability of the Hall effect with the ambipolar diffusion in the outer regions of the clouds.

Keywords: magnetic fields
Theoretical Systematics in Testing the Cosmological Principle with the Kinematic Quasar Dipole

The Cosmological Principle (CP) is part of the foundation that underpins the standard model of the Universe. In the era of precision cosmology, when stress tests of the standard model are uncovering various tensions and possible anomalies, it is critical to check the viability of this principle. A key test is the consistency between the kinematic dipoles of the cosmic microwave background and of the large-scale matter distribution. Results using radio continuum and quasar samples indicate a rough agreement in the directions of the two dipoles, but a larger than expected amplitude of the matter dipole. The resulting tension with the radiation dipole has been estimated at ~5σ for some cases, suggesting a potential new cosmological tension and a possible violation of the CP. However, the standard formalism for predicting the dipole in the two-dimensional projection of sources overlooks possible evolution effects in the luminosity function. In fact, radial information from the luminosity function is necessary for a correct projection of the three-dimensional source distribution. Using a variety of current models of the quasar luminosity function, we show that neglecting redshift evolution can significantly overestimate the relative velocity amplitude. While the models we investigate are consistent with each other and with current data, the dipole derived from these, which depends on derivatives of the luminosity function, can disagree by more than 3σ. This theoretical systematic bias needs to be resolved before robust conclusions can be made about a new cosmic tension.

Keywords: cosmology; cosmological principle; large-scale structure of the universe; quasars; luminosity function
Point Source C-band Mueller Matrices for the Green Bank Telescope

C-band Mueller matrices for the Green Bank Telescope are presented here which enable on-sky Stokes parameters for point sources at the beam center to be determined. Standard calibrators, 3C 138 and 3C 286, were observed using the Spider program to steer the telescope across a broad range of R.A. on both sides of the zenith transit. For this analysis, only the observations at the peak of the Spider pattern were used rather than the full sweep of the runs. Therefore, the results presented here only apply to point sources at the beam center. The Mueller matrices are shown to vary with frequency and with use of the Hi-Cal or Lo-Cal noise diodes, due to the relative calibration gain between the X and Y components of the feed. However, the relative calibration gain can be determined from observations of a source with known polarization. Correcting the data for the relative calibration gain prior to data analysis allows for use of a frequency-independent Mueller matrix. This generic Mueller matrix is shown to provide reliable C-band polarization measurements.

Keywords: astronomical instrumentation; polarimetry; radio telescopes; software documentation; calibration
Hints of a Population of Solar System Analog Planets from ALMA

The recent Atacama Large Millimeter/submillimeter Array (ALMA) Disk Substructures at High Angular Resolution Project (DSHARP) survey provided illuminating results on the diversity of substructures in planet-forming disks. These substructures trace pebble-sized grains accumulated at local pressure maxima, possibly due to planet-disk interactions or other planet formation processes. DSHARP sources are heavily biased to large and massive disks that only represent the high (dust flux) tail end of the disk population. Thus it is unclear whether similar substructures and corresponding physical processes also occur in the majority of disks that are fainter and more compact. Here we explore the presence and characteristics of features in a compact disk around GQ Lup A, the effective radius of which is 1.5-10 times smaller than those of DSHARP disks. We present our analysis of ALMA 1.3 mm continuum observations of the GQ Lup system. By fitting visibility profiles of the continuum emission, we find substructures including a gap at ∼10 au. The compact disk around GQ Lup exhibits similar substructures to those in the DSHARP sample, suggesting that mechanisms of trapping pebble-sized grains are at work in small disks as well. Characteristics of the feature at ∼10 au, if due to a hidden planet, are evidence of planet formation at Saturnian distances. Our results hint at a rich world of substructures to be identified within the common population of compact disks, and subsequently a population of solar system analogs within these disks. Such study is critical to understanding the formation mechanisms and planet populations in the majority of protoplanetary disks.

Keywords: protoplanetary disks; planet formation; circumstellar disks
Characterizing the Evolved Stellar Population in the Galactic Foreground. I. Bolometric Magnitudes, Spatial Distribution and Period-Luminosity Relations

Radio campaigns using maser stellar beacons have provided crucial information to characterize Galactic stellar populations. Currently, the Bulge Asymmetries and Dynamical Evolution (BAaDE) project is surveying infrared (IR) color-selected targets for SiO masers. This provides a sample of evolved stars that can be used to study the inner, optically obscured Galaxy using line-of-sight velocities and possibly very long baseline interferometry proper motions. In order to use the BAaDE sample for kinematic studies, the stellar population should be characterized. In this study, the BAaDE targets have been cross-matched with IR (2MASS) and optical (Gaia) samples. By exploring the synergies of this cross-match together with Gaia parallaxes and extinction maps, the local (d < 2 kpc) asymptotic giant branch (AGB) stars can be characterized. We have defined a BAaDE-Gaia sample of 20,111 sources resulting from cross-matching BAaDE targets with IR and optical surveys. From this sample, a local sample of 1812 evolved stars with accurate parallax measurements, confirmed evolved stellar evolution stage, and within 2 kpc distance around the Sun was selected, for which absolute (bolometric) magnitudes are estimated. The evolved stellar population with Gaia counterparts that are variable seems to be predominantly associated with AGB stars with moderate luminosity ( ${1500}_{-500}^{+3000}\ {L}_{\odot }$ ) and periods between 250 and 1250 days.

Keywords: galaxy stellar content; solar neighborhood; asymptotic giant branch stars; periodic variable stars; astrometry; surveys
Alfvénicity-related Long Recovery Phases of Geomagnetic Storms: A Space Weather Perspective

This paper reports, for the first time on a statistical basis, on the key role played by the Alfvénic fluctuations in modulating the recovery phase of the geomagnetic storms, slowing down the restoration of the magnetosphere toward its pre-storm equilibrium state. Using interplanetary and geomagnetic measurements collected over more than one solar cycle, a high correlation between the durations of Alfvénic streams and concurrent recovery phases is found, pointing to a clear coupling between Alfvénic turbulence and magnetospheric ring current dynamics. By exploiting current solar wind models, these observations also provide space weather opportunities of predicting the total duration of any geomagnetic storm induced by any solar driver provided that it is followed by an Alfvénic stream, a crucial piece of information for ground technologies and infrastructures that are affected by time-integrated effects throughout the duration of the storm.

Keywords: magnetohydrodynamics; alfven waves; space plasmas; interplanetary turbulence; solar-terrestrial interactions; space weather; solar wind; heliosphere; solar storm; interplanetary medium; time series analysis
Rovibrational Spectroscopy of CI Tau-Evidence of a Multicomponent Eccentric Disk Induced by a Planet

CI Tau is currently the only T Tauri star with an inner protoplanetary disk that hosts a planet, CI Tau b, that has been detected by a radial velocity survey. This provides the unique opportunity to study disk features that were imprinted by that planet. We present multiepoch spectroscopic data, taken with NASA IRTF in 2022, of the 12CO and hydrogen Pfβ line emissions spanning nine consecutive nights, which is the proposed orbital period of CI Tau b. We find that the star's accretion rate varied according to that nine-day period, indicative of companion-driven accretion. Analysis of the 12CO emission lines reveals that the disk can be described with an inner and an outer component spanning orbital radii 0.05-0.13 au and 0.15-1.5 au, respectively. Both components have eccentricities of about 0.05 and arguments of periapsis that are oppositely aligned. We present a proof-of-concept hydrodynamic simulation that shows that a massive companion on a similarly eccentric orbit can recreate a similar disk structure. Our results allude to such a companion being located at an orbital distance of around 0.14 au. However, this planet's orbital parameters may be inconsistent with those of CI Tau b, whose high eccentricity is likely not compatible with the low disk eccentricities inferred by our model.

Keywords: protoplanetary disks; circumstellar disks; stellar accretion; accretion; planetary-disk interactions; hot jupiters; high resolution spectroscopy; infrared spectroscopy
Visualizing the Number of Existing and Future Gravitational-wave Detections from Merging Double Compact Objects

How many gravitational-wave observations from double compact object mergers have we seen to date? This seemingly simple question surprisingly yields a somewhat ambiguous answer that depends on the chosen data-analysis pipeline, detection threshold, and other underlying assumptions. To illustrate this we provide visualizations of the number of existing detections from double compact object mergers by the end of the third observing run (O3) based on recent results from the literature. Additionally, we visualize the expected number of observations from future-generation detectors, highlighting the possibility of up to millions of detections per year by the time next-generation ground-based detectors like Cosmic Explorer and Einstein Telescope come online. We present a publicly available code that highlights the exponential growth in gravitational-wave observations in the coming decades and the exciting prospects of gravitational-wave (astro)physics.

Keywords: gravitational wave sources; gravitational waves; compact objects
Possible Evidence from the Flaring Activity of Sgr A* for a Star at a Distance of ∼3.3 Schwarzschild Radii from the Black Hole

The frequent flaring events in the X-ray and the near-IR (NIR) radiation of Sgr A* seem not to be periodic in time. However, statistical regularities, here termed "modulations by a pacemaker," are found in the recorded arrival times of both types of events. The characteristic time of the X-ray pacemaker is 149 minutes, and that of the NIR pacemaker is 40 minutes. Their reality as derived from observed data can be accepted at larger than 4.6σ and 3.8σ levels of statistical confidence, respectively. These results can be interpreted as evidence for a star that revolves around the black hole (BH) of Sgr A* in a slightly elliptical precessing orbit, at a distance of 3-3.5 Schwarzschild radii of the BH. The period of the X-ray pacemaker, which is not a periodicity of the flare occurrences themselves, is the epicyclic period of the star orbital motion. This is the time interval between two successive passages of the star through the pericenter of its orbit. The NIR pacemaker period is the mean sidereal binary period of the star revolution. The origin of the X-ray flares is in episodes of intense mass loss from the star that occur preferably near the pericenter phase of the binary revolution. The NIR flares originate or are triggered by processes that are internal to the star. The radiation emitted in the direction of Earth is slightly modulated by the changing aspect ratio of the two components of the BH/star binary to the line of sight from Earth at the sidereal binary frequency.

Keywords: black hole physics; galactic center; x-ray bursts; infrared sources; x-ray sources
A Hard Look at Relativistic Reverberation in MCG-5-23-16 and SWIFT J2127.4+5654: Testing the Lamppost Model

X-ray reverberation mapping has emerged as a new tool to probe accretion in active galactic nuclei (AGN), providing a potentially powerful probe of accretion at the black hole scale. The lags, along with relativistic spectral signatures are often interpreted in light of the lamppost model. Focusing specifically on testing the prediction of the relativistic reverberation model, we have targeted several of the brightest Seyfert Galaxies in X-rays with different observing programs. Here, we report the results from two large campaigns with NuSTAR targeting MCG-5-23-16 and SWIFT J2127.4+5654 to test the model predictions in the 3-50 keV band. These are two of three sources that showed indications of a delayed Compton hump in early data. With triple the previously analyzed exposures, we find no evidence for relativistic reverberation in MCG-5-23-16, and the energy-dependent lags are consistent with a log-linear continuum. In SWIFT J2127.4+5654, although a continuum-only model explains the data, the relativistic reverberation model provides a significant improvement to the energy and frequency-dependent lags, but with parameters that are not consistent with the time-averaged spectrum. This adds to mounting evidence showing that the lag data is not consistent with a static lamppost model.

Keywords: active galactic nuclei; high energy astrophysics; x-ray active galactic nuclei; astrophysical black holes
The Sonora Brown Dwarf Atmosphere and Evolution Models. I. Model Description and Application to Cloudless Atmospheres in Rainout Chemical Equilibrium

We present a new generation of substellar atmosphere and evolution models, appropriate for application to studies of L-, T-, and Y-type brown dwarfs and self-luminous extrasolar planets. The models describe the expected temperature-pressure profiles and emergent spectra of atmospheres in radiative-convective equilibrium with effective temperatures and gravities within the ranges 200 ≤ Teff ≤ 2400 K and $2.5\leqslant \mathrm{log}g\leqslant 5.5$ . These ranges encompass masses from about 0.5 to 85 Jupiter masses for a set of metallicities ([M/H] = - 0.5 to + 0.5), C/O ratios (from 0.5 to 1.5 times that of solar), and ages. These models expand the diversity of model atmospheres currently available, notably to cooler effective temperatures and greater ranges in C/O. Notable improvements from past such models include updated opacities and atmospheric chemistry. Here we describe our modeling approach and present our initial tranche of models for cloudless, chemical equilibrium atmospheres. We compare the modeled spectra, photometry, and evolution to various data sets.

Keywords: brown dwarfs; t dwarfs; l dwarfs; l subdwarfs; t subdwarfs; y dwarfs; stellar atmospheres
High-soft to Low-hard State Transition in Black Hole X-Ray Binaries with GRMHD Simulations

To understand the decaying phase of outbursts in the black hole (BH) X-ray binaries (BH-XRBs), we performed very long general relativistic magnetohydrodynamic simulations of a geometrically thin accretion disk around a Kerr BH with slowly rotating matter injected from outside. We thoroughly studied the flow properties, dynamical behavior of the accretion rate, magnetic flux rate, and jet properties during the temporal evolution. Due to the interaction between the thin disk and injected matter, the accretion flow near the BH goes through different phases. The sequence of phases is: soft state → soft-intermediate state → hard-intermediate state → hard state → quiescent state. For the accretion rate (and hence the luminosity) to decrease (as observed) in our model, the mass injection should not decay slower than the angular momentum injection. We also observed quasiperiodic oscillations (QPOs) in the accretion flow. Throughout the evolution, we observed low-frequency QPOs (~10 Hz) and high-frequency QPOs (~200 Hz). Our simple unified accretion flow model for state transitions is able to describe outbursts in BH-XRBs.

Keywords: accretion; black hole physics; magnetohydrodynamics; x-ray binary stars