adsabs/SciX_UAT_keywords huggingface dataset:
Unresolved z 8 Point Sources and Their Impact on the Bright End of the Galaxy Luminosity Function

The distribution and properties of the first galaxies and quasars are critical pieces of the puzzle in understanding galaxy evolution and cosmic reionization. Previous studies have often excluded unresolved sources as potential low-redshift interlopers. We combine broadband color and photometric redshift analysis with morphological selections to identify a robust sample of candidates consistent with unresolved point sources at redshifts z ~ 8 using deep Hubble Space Telescope images. We also examine G141 grism spectroscopic data to identify and eliminate dwarf star contaminants. From these analyses, we identify three bright (M UV ≲ -22 AB mag) dropout point sources at 7.5 < z < 8.1. Spectral energy distribution analyses suggest that these sources are either quasars or compact star-forming galaxies. The flux captured by the IRAC 4.5 μm channel suggests that they have moderate Hβ + [O III] equivalent widths. We calculate the number density of point sources at z ~ 7-8, and find that a double-power-law model well describes the point-source distribution. We then extend our analysis to estimate the combined point-source + galaxy luminosity function and find that the point sources have a nonnegligible contribution to the bright-end excess. The fact that the point sources dominate only at M UV ≲ -22 suggests that their contribution to cosmic reionization is likely limited. While spectroscopic follow-up is needed to confirm the nature of these point sources, this work demonstrates that the inclusion of Lyman-dropout point sources is necessary for a complete census of early galaxies at the epoch of cosmic reionization.

Keywords: hubble space telescope; high-redshift galaxies; galaxy formation; galaxy photometry; quasars; luminosity function; reionization
Leveraging Space-based Data from the Nearest Solar-type Star to Better Understand Stellar Activity Signatures in Radial Velocity Data

Stellar variability is a key obstacle in reaching the sensitivity required to recover Earth-like exoplanetary signals using the radial velocity (RV) detection method. To explore activity signatures in Sun-like stars, we present SolAster, a publicly distributed analysis pipeline 10 10 https://tamarervin.github.io/SolAster/ that allows for comparison of space-based measurements with ground-based disk-integrated RVs. Using high-spatial-resolution Dopplergrams, magnetograms, and continuum filtergrams from the Helioseismic and Magnetic Imager aboard the Solar Dynamics Observatory (SDO), we estimate "Sun-as-a-star" disk-integrated RVs due to rotationally modulated flux imbalances and convective blueshift suppression, as well as other observables such as unsigned magnetic flux. Comparing these measurements with ground-based RVs from the NEID instrument, which observes the Sun daily using an automated solar telescope, we find a strong relationship between magnetic activity indicators and RV variation, supporting efforts to examine unsigned magnetic flux as a proxy for stellar activity in slowly rotating stars. Detrending against measured unsigned magnetic flux allows us to improve the NEID RV measurements by ~20% (~50 cm s-1 in a quadrature sum), yielding an rms scatter of ~60 cm s-1 over five months. We also explore correlations between individual and averaged spectral line shapes in the NEID spectra and SDO-derived magnetic activity indicators, motivating future studies of these observables. Finally, applying SolAster to archival planetary transits of Venus and Mercury, we demonstrate the ability to recover small amplitude (<50 cm s-1) RV variations in the SDO data by directly measuring the Rossiter-McLaughlin signals.

Keywords: exoplanets; radial velocity; the sun
High-precision Calibration of the Fluxgate Magnetometer Offset Vector in the Terrestrial Magnetosheath

High-precision magnetic field measurements are of great significance for the in-depth study of the physical processes in the astrophysical plasma environment. To obtain accurate natural magnetic fields, in-flight calibration is one key step to obtaining zero offset of the spaceborne fluxgate magnetometer (FGM). Mirror mode structures, widely existing in the solar wind and planetary magnetosheaths and magnetospheres, can be used to calculate the zero offset. However, it is difficult to obtain an accurate zero offset by the current methods using mirror mode structures in the planetary magnetosheath. Here, we develop a new method to calculate the zero offset of the spaceborne FGM using magnetic dips, which are a kind of mirror mode structure. This method is based on the assumption that the magnetic field is zero in the cross section of the magnetic dip. Our method is able to calculate the zero offset using only one magnetic dip. We test this method by using the data from the Magnetospheric Multiscale Mission, and find that the calculation errors of 78.1% of the estimated zero offsets are <0.5 nT when using 25 magnetic dips in the terrestrial magnetosheath. This suggests that our method is able to achieve a high accuracy of the zero offset in the planetary magnetosheath.

Keywords: solar wind; planetary magnetospheres; magnetic fields
Periodic Modulation: Newly Emergent Emission Behavior in Pulsars

Periodic modulations are seen in normal pulsars (P > 0.1 s) over timescales ranging from a few seconds to several minutes. Such modulations have usually been associated with the phenomenon of subpulse drifting. A number of recent studies have shown subpulse drifting to exhibit very specific physical characteristics: (I) drifting is seen only in conal components of the pulse profile and is absent in central core emission; (II) drifting pulsars are distributed over a narrow range of spin-down energy loss ( $\dot{E}$ ), where pulsars with $\dot{E}\,\lt $ 2 × 1032 erg s-1 show this behavior; and (III) drifting periodicity (P3) is anti-correlated with $\dot{E}$ , such that pulsars with lower values of $\dot{E}$ tend to have longer P3. These detailed characterizations of drifting behavior, on the other hand, also revealed the presence of other distinct periodic modulations, which can be broadly categorized into two types, periodic nulling, and periodic amplitude modulation. In contrast to drifting, these periodic phenomena are seen across the entire profile in both the core and conal components simultaneously and are not restricted to any specific $\dot{E}$ range. In this work we have assembled an exhaustive list of around 70 pulsars that show such periodic modulations, 22 of which were newly detected using observations from the Giant Meterwave Radio Telescope and the remaining compiled from past publications. The presence of such a significant group in the pulsar population suggests periodic modulations to be newly emergent phenomena in pulsars, with a physical origin that is distinct from that of subpulse drifting.

Keywords: radio pulsars; pulsars
Fermi-LAT Gamma-Ray Emission Discovered from the Composite Supernova Remnant B0453-685 in the Large Magellanic Cloud

We report the second extragalactic pulsar wind nebula (PWN) to be detected in the megaelectronvolt-gigaelectronvolt band by the Fermi-LAT, located within the Large Magellanic Cloud. The only other known PWN to emit in the Fermi band outside of the Milky Way is N157B, which lies to the west of the newly detected gamma-ray emission at an angular distance of 4°. Faint, pointlike gamma-ray emission is discovered at the location of the composite supernova remnant (SNR) B0453-685 with a ~4σ significance with energies ranging from 300 MeV-2 TeV. We present the Fermi-LAT data analysis of the new gamma-ray source, coupled with a detailed multiwavelength investigation to understand the nature of the observed emission. Combining the observed characteristics of the SNR and the physical implications from broadband modeling, we argue it is unlikely that the SNR is responsible for the gamma-ray emission. While the gamma-ray emission is too faint for a pulsation search, we try to distinguish between any pulsar and PWN component of SNR B0453-685 that could be responsible for the observed gamma-ray emission using semi-analytic models. We determine the most likely scenario is that the old PWN (τ ~ 14,000 yr) within B0453-685 has been impacted by the return of the SNR reverse shock with a possible substantial pulsar component below 5 GeV.

Keywords: gamma-ray astronomy; large magellanic cloud; x-ray astronomy; supernova remnants; pulsar wind nebulae
A Binary Origin for the First Isolated Stellar-mass Black Hole Detected with Astrometric Microlensing

The Milky Way is believed to host hundreds of millions of quiescent stellar-mass black holes (BHs). In the last decade, some of these objects have been potentially uncovered via gravitational microlensing events. All these detections resulted in a degeneracy between the velocity and the mass of the lens. This degeneracy has been lifted, for the first time, with the recent astrometric microlensing detection of OB110462. However, two independent studies reported very different lens masses for this event. Sahu et al. inferred a lens mass of 7.1 ± 1.3 M ⊙, consistent with a BH, while Lam et al. inferred 1.6-4.2 M ⊙, consistent with either a neutron star or a BH. Here, we study the landscape of isolated BHs formed in the field. In particular, we focus on the mass and center-of-mass speed of four subpopulations: isolated BHs from single-star origin, disrupted BHs of binary-star origin, main-sequence stars with a compact object companion, and double compact object mergers. Our model predicts that most (≳70%) isolated BHs in the Milky Way are of binary origin. However, noninteractions lead to most massive BHs (≳15-20 M ⊙) being predominantly of single origin. Under the assumption that OB110462 is a free-floating compact object, we conclude that it is more likely to be a BH originally belonging to a binary system. Our results suggest that low-mass BH microlensing events can be useful to understand binary evolution of massive stars in the Milky Way, while high-mass BH lenses can be useful to probe single stellar evolution.

Keywords: astrophysical black holes; gravitational microlensing; binary stars; gravitational waves
Inferring Line-of-sight Velocities and Doppler Widths from Stokes Profiles of GST/NIRIS Using Stacked Deep Neural Networks

Obtaining high-quality magnetic and velocity fields through Stokes inversion is crucial in solar physics. In this paper, we present a new deep learning method, named Stacked Deep Neural Networks (SDNN), for inferring line-of-sight (LOS) velocities and Doppler widths from Stokes profiles collected by the Near InfraRed Imaging Spectropolarimeter (NIRIS) on the 1.6 m Goode Solar Telescope (GST) at the Big Bear Solar Observatory (BBSO). The training data for SDNN are prepared by a Milne-Eddington (ME) inversion code used by BBSO. We quantitatively assess SDNN, comparing its inversion results with those obtained by the ME inversion code and related machine-learning (ML) algorithms such as multiple support vector regression, multilayer perceptrons, and a pixel-level convolutional neural network. Major findings from our experimental study are summarized as follows. First, the SDNN-inferred LOS velocities are highly correlated to the ME-calculated ones with the Pearson product-moment correlation coefficient being close to 0.9 on average. Second, SDNN is faster, while producing smoother and cleaner LOS velocity and Doppler width maps, than the ME inversion code. Third, the maps produced by SDNN are closer to ME's maps than those from the related ML algorithms, demonstrating that the learning capability of SDNN is better than those of the ML algorithms. Finally, a comparison between the inversion results of ME and SDNN based on GST/NIRIS and those from the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory in flare-prolific active region NOAA 12673 is presented. We also discuss extensions of SDNN for inferring vector magnetic fields with empirical evaluation.

Keywords: solar atmosphere; solar magnetic fields; convolutional neural networks
Unraveling Twisty Linear Polarization Morphologies in Black Hole Images

We investigate general relativistic magnetohydrodynamic simulations to determine the physical origin of the twisty patterns of linear polarization seen in spatially resolved black hole images and explain their morphological dependence on black hole spin. By characterizing the observed emission with a simple analytic ring model, we find that the twisty morphology is determined by the magnetic field structure in the emitting region. Moreover, the dependence of this twisty pattern on spin can be attributed to changes in the magnetic field geometry that occur due to the frame dragging. By studying an analytic ring model, we find that the roles of Doppler boosting and lensing are subdominant. Faraday rotation may cause a systematic shift in the linear polarization pattern, but we find that its impact is subdominant for models with strong magnetic fields and modest ion-to-electron temperature ratios. Models with weaker magnetic fields are much more strongly affected by Faraday rotation and have more complicated emission geometries than can be captured by a ring model. However, these models are currently disfavoured by the recent EHT observations of M87*. Our results suggest that linear polarization maps can provide a probe of the underlying magnetic field structure around a black hole, which may then be usable to indirectly infer black hole spins. The generality of these results should be tested with alternative codes, initial conditions, and plasma physics prescriptions.

Keywords: black hole physics; event horizons; plasma astrophysics; magnetohydrodynamical simulations
REQUIEM-2D Methodology: Spatially Resolved Stellar Populations of Massive Lensed Quiescent Galaxies from Hubble Space Telescope 2D Grism Spectroscopy

We present a novel Bayesian methodology to jointly model photometry and deep Hubble Space Telescope 2D grism spectroscopy of high-redshift galaxies. Our requiem2d code measures both unresolved and resolved stellar populations, ages, and star formation histories (SFHs) for the ongoing REsolving QUIEscent Magnified (REQUIEM) Galaxies Survey, which targets strong gravitationally lensed quiescent galaxies at z ∼ 2. We test the accuracy of requiem2d using a simulated sample of massive galaxies at z ∼ 2 from the Illustris cosmological simulation and find that we recover the general trends in SFH and median stellar ages. We further present a pilot study for the REQUIEM Galaxies Survey: MRG-S0851, a quintuply imaged, massive ( $\mathrm{log}{M}_{* }/{M}_{\odot }=11.02\pm 0.04$ ) red galaxy at z = 1.883 ± 0.001. With an estimated gravitational magnification of $\mu ={5.7}_{-0.2}^{+0.4}$ , we sample the stellar populations on 0.6 kpc physical size bins. The global mass-weighted median age is constrained to be ${1.8}_{-0.2}^{+0.3}$ Gyr, and our spatially resolved analysis reveals that MRG-S0851 has a flat age gradient in the inner 3 kpc core after taking into account the subtle effects of dust and metallicity on age measurements, favoring an early formation scenario. The analysis for the full REQUIEM-2D sample will be presented in a forthcoming paper with a beta release of the requiem2d code.

Keywords: galaxy formation; high-redshift galaxies; galaxy stellar content; galaxy quenching; strong gravitational lensing
Recovering Cosmic Microwave Background Polarization Signals with Machine Learning

Primordial B-mode detection is one of the main goals of current and future cosmic microwave background (CMB) experiments. However, the weak B-mode signal is overshadowed by several Galactic polarized emissions, such as thermal dust emission and synchrotron radiation. Subtracting foreground components from CMB observations is one of the key challenges in searching for the primordial B-mode signal. Here, we construct a deep convolutional neural network (CNN) model, called CMBFSCNN (Cosmic Microwave Background Foreground Subtraction with CNN), which can cleanly remove various foreground components from simulated CMB observational maps at the sensitivity of the CMB-S4 experiment. Noisy CMB Q (or U) maps are recovered with a mean absolute difference of 0.018 ± 0.023 μK (or 0.021 ± 0.028 μK). To remove the residual instrumental noise from the foreground-cleaned map, inspired by the needlet internal linear combination method, we divide the whole data set into two "half-split maps," which share the same sky signal, but have uncorrelated noise, and perform a cross-correlation technique to reduce the instrumental noise effects at the power spectrum level. We find that the CMB EE and BB power spectra can be precisely recovered with significantly reduced noise effects. Finally, we apply this pipeline to current Planck observations. As expected, various foregrounds are cleanly removed from the Planck observational maps, with the recovered EE and BB power spectra being in good agreement with the official Planck results.

Keywords: cosmic microwave background radiation; observational cosmology; convolutional neural networks
The Imprint of Intermittent Interchange Reconnection on the Solar Wind

The solar wind is known to be highly structured in space and time. Observations from Parker Solar Probe have revealed an abundance of so-called magnetic switchbacks within the near-Sun solar wind. In this Letter, we use a high-resolution, adaptive-mesh, magnetohydrodynamics simulation to explore the disturbances launched into the solar wind by intermittent/bursty interchange reconnection and how they may be related to magnetic switchbacks. We find that repeated ejection of plasmoid flux ropes into the solar wind produces a curtain of propagating and interacting torsional Alfvénic waves. We demonstrate that this curtain forms when plasmoid flux ropes dynamically realign with the radial field as they are ejected from the current layer and that this is a robust effect of the 3D geometry of the interchange reconnection region. Simulated flythroughs of this curtain in the low corona reveal an Alfvénic patch that closely resembles observations of switchback patches, but with relatively small magnetic field deflections. Therefore, we suggest that switchbacks could be the solar wind imprint of intermittent interchange reconnection in the corona, provided an in situ process subsequently amplifies the disturbances to generate the large deflections or reversals of radial field that are typically observed. That is to say, our results indicate that a combination of low-coronal and inner-heliospheric mechanisms may be required to explain switchback observations.

Keywords: solar corona; solar coronal holes; solar wind; solar magnetic reconnection; solar magnetic fields; solar physics
Broken Power-law Energy Spectra of the Accelerated Electrons Detected in Radio and Hard X-Rays during the SOL2013-05-13 Event

Solar flares, resulting from magnetic activity of the Sun, are among the most energetic events in the solar system and in extreme cases directly affect our highly technological society. In this work, we analyze a solar flare detected at millimeter and centimeter wavelengths, as well as X-rays above 1 MeV. Observations of solar flares at these energy bands provide diagnostics of the energetic accelerated electrons and the magnetic fields where the emission is produced. During the SOL2013-05-13 solar flare, radio data were obtained by the telescope system POlarisation Emission of Millimeter Activity at the Sun, which observes the Sun at 45 and 90 GHz with polarization measurements, and at microwaves (1-15 GHz) by the Radio Solar Telescope Network. For the same event, X-ray emission was detected by the RHESSI and Fermi satellites. Spectra at both wavelengths were constructed and fit separately to yield the accelerated electron energy distribution that produced the emission. The optically thin radio spectral index was calculated by fitting the Ramaty model of gyrosynchrotron emission to the observed radio spectrum, whereas the hard X-ray spectral index was obtained from the spectral fit assuming a thermal emission model plus a nonthermal broken power-law distribution. Finally, both spectral indexes were compared and confirmed that the index obtained from the radio spectrum agrees with the index of the X-ray spectrum for energies above the break energy of ~600 keV. Thus, the hard X-rays more energetic than 600 keV and high radio frequencies of solar flares are emitted by the same population of high-energy accelerated electrons. This result indicates that the accelerated electrons have an energy distribution best represented by a broken power law, with a breakup above energies around 1 MeV.

Keywords: x-ray transient sources
The Long-term Spectroscopic and Photometric Behavior of the Carbon Star RS Cygni

RS Cygni is a semiregular variable carbon star that has a distinctive light curve. Twenty-one years of optical spectroscopic and photometric observations of this star made at Grinnell College have been used not only to produce a comprehensive survey of the behavior of this star but also to compare these two sets of data. A number of spectral features vary in strength with the cycle of the star and some, but not all, of this variation is correlated with the dips that often occur near the maxima of the light curve. In particular, the strengths of the Balmer emission lines often have two peaks per cycle. Such correlation might be consistent with a mechanism for producing the dips, such as dust formation, that reduces the brightness in a way that does not involve rapid changes in photospheric characteristics. The large amount of data and the precision of the photometry presented give an unusually detailed view of how the light of RS Cyg varies over time.

Keywords: spectroscopy; bv photometry; circumstellar dust; semi-regular variable stars; carbon stars
Understanding How Fast Black Holes Spin by Analyzing Data from the Second Gravitational-wave Catalogue

The Advanced LIGO and Virgo detectors have now observed approximately 50 black hole binary mergers, from which we can begin to infer how rapidly astrophysical black holes spin. The LIGO-Virgo Collaboration (LVC) analysis of detections up to the end of the first half of the third observing run (O3a) appeared to uncover a distribution of spin magnitudes that peaks at ~0.2. This is surprising: is there a black hole formation mechanism that prefers a particular, nonzero spin magnitude, or could this be the cumulative effect of multiple formation processes? We perform an independent analysis of the most recent gravitational-wave (GW) catalog, and find that (a) the support for the LVC spin magnitude is tenuous; in particular, adding or removing just one signal from the catalog can remove the statistical preference for this distribution; and (b) we find potential evidence for two spin subpopulations in the observed black holes: one with extremely low spins and one with larger spin magnitudes. We make the connection that these spin subpopulations could be correlated with the mass of the binary, with more massive binaries preferring larger spin magnitudes, and argue that this may provide evidence for hierarchical mergers in the second GW catalog.

Keywords: black hole physics; gravitational waves