adsabs/SciX_UAT_keywords huggingface dataset:
Galaxy Merger Rates up to z ∼ 3 Using a Bayesian Deep Learning Model: A Major-merger Classifier Using IllustrisTNG Simulation Data

Merging is potentially the dominant process in galaxy formation, yet there is still debate about its history over cosmic time. To address this, we classify major mergers and measure galaxy merger rates up to z ∼ 3 in all five CANDELS fields (UDS, EGS, GOODS-S, GOODS-N, COSMOS) using deep learning convolutional neural networks trained with simulated galaxies from the IllustrisTNG cosmological simulation. The deep learning architecture used is objectively selected by a Bayesian optimization process over the range of possible hyperparameters. We show that our model can achieve 90% accuracy when classifying mergers from the simulation and has the additional feature of separating mergers before the infall of stellar masses from post-mergers. We compare our machine-learning classifications on CANDELS galaxies and compare with visual merger classifications from Kartaltepe et al., and show that they are broadly consistent. We finish by demonstrating that our model is capable of measuring galaxy merger rates, ${ \mathcal R }$ , that are consistent with results found for CANDELS galaxies using close pairs statistics, with ${ \mathcal R }{(z)=0.02\pm 0.004\times (1+z)}^{2.76\pm 0.21}$ . This is the first general agreement between major mergers measured using pairs and structure at z < 3.

Keywords: galaxy mergers; convolutional neural networks
Subaru Medium-resolution Spectra of a QSO at z = 6.62: Three Reionization Tests

Investigating the Gunn-Peterson (GP) trough of high-redshift quasars (QSOs) is a powerful way to reveal the cosmic reionization. As one of such attempts, we perform a series of analyses to examine the absorption lines observed with one of the highest-redshift QSOs, PSO J006.1240+39.2219, which we previously discovered at z = 6.62. Using the Subaru telescope, we obtained medium-resolution spectrum with a total exposure time of 7.5 hr. We calculate the Lyα transmission in different redshift bins to determine the near zone radius and the optical depth at 5.6 < z < 6.5. We find a sudden change in the Lyα transmission at 5.75 < z < 5.86, which is consistent with the result from the literature. The near zone radius of the QSO is 5.79 ± 0.09 pMpc, within the scatter of the near zone radii of other QSOs measured in previous studies. We also analyze the dark gap distribution to probe the neutral hydrogen fractions beyond the saturation limit of the GP trough. We extend the measurement of the dark gaps to 5.7 < z < 6.3. We find that the gap widths increase with increasing redshifts, suggesting more neutral universe at higher redshifts. However, these measurements strongly depend on the continuum modeling. As a continuum model-free attempt, we also perform the dark pixel counting analysis to find the upper limit of $\langle {X}_{{\rm{H}}{\rm{I}}}\rangle \sim 0.6$ (0.8) at z < 5.8 (z > 5.8). All three analyses based on this QSO show increasingly neutral hydrogen toward higher redshifts, adding precious measurements up to z ∼ 6.5.

Keywords: reionization; early universe; quasars; quasar absorption line spectroscopy; observational cosmology; intergalactic medium; intergalactic medium phases
Observations of Magnetospheric Solar Wind Charge Exchange

The study of solar wind charge exchange (SWCX) emission is vital to both the X-ray astrophysics and heliophysics communities. SWCX emission contaminates all astrophysical observations in X-rays regardless of the direction. Ignoring this contribution to X-ray spectra can lead to erroneous conclusions regarding the astrophysical plasmas along the line of sight owing to the similar spectral distributions of SWCX and several common types of more distant astrophysical plasmas. Since its discovery, the literature has distinguished between diffuse SWCX emission resulting from solar wind-neutral interactions within Earth's magnetosphere, called magnetospheric SWCX, and similar interactions occurring more generally throughout the heliosphere, called heliospheric SWCX. Here we build on previous work validating a modeling method for the heliospheric SWCX contribution in X-ray spectra obtained with a medium-resolution CubeSat instrument named HaloSat at low ecliptic latitudes. We now apply this model to a specially designed set of extended observations with the same instrument and successfully separate the spectral contributions of the astrophysical background and the heliospheric SWCX from the remaining contributions. Specifically, we find significant excess emission for four observations in the O VII emission line not explained by other sources, possibly indicative of magnetospheric SWCX. We discuss these results in comparison with simulation results publicly available through the Community Coordinated Modeling Center. We also report an absorbed high-temperature component in 2 of the 12 fields of view analyzed.

Keywords: solar wind; diffuse x-ray background
Resolving the Emission Regions of the Crab Pulsar's Giant Pulses. II. Evidence for Relativistic Motion

The Crab Pulsar is the prime example of an emitter of giant pulses. These short, very bright pulses are thought to originate near the light cylinder, at ~1600 km from the pulsar. The pulsar's location inside the Crab Nebula offers an unusual opportunity to resolve the emission regions, using the nebula, which scatters radio waves, as a lens. We attempt to do this using a sample of 61,998 giant pulses found in coherently combined European VLBI network observations at 18 cm. These were taken at times of relatively strong scattering and hence good effective resolution. From correlations between pulse spectra, we show that the giant pulse emission regions are indeed resolved. We infer apparent diameters of ~2000 and ~2400 km for the main and interpulse components, respectively, and show that with these sizes the correlation amplitudes and decorrelation timescales and bandwidths can be understood quantitatively, both in our observations and in previous ones. Using pulse-spectra statistics and correlations between polarizations, we also show that the nebula resolves the nanoshots that comprise individual giant pulses. The implied diameters of ~1100 km far exceed light-travel-time estimates, suggesting the emitting plasma is moving relativistically, with γ ≃ 104, as inferred previously from drifting bands during the scattering tail of a giant pulse. If so, the emission happens over a region extended along the line of sight by ~107 km. We conclude that relativistic motion likely is important for producing giant pulses, and may be similarly for other sources of short, bright radio emission, such as fast radio bursts.

Keywords: pulsars; interstellar scintillation; radio bursts; very long baseline interferometry; supernova remnants
Semi-implicit Solver for the Heat Equation with Stefan–Boltzmann Law Boundary Condition

The surface energy balance on an atmosphereless body consists of solar irradiance, subsurface heat conduction, and thermal radiation to space by the Stefan–Boltzmann law. Here we extend the semi-implicit Crank–Nicolson method to this specific nonlinear boundary condition and validate its accuracy. A rapid change in incoming solar flux can cause a numerical instability, and several approaches to dampen this instability are analyzed. A predictor based on the Volterra integral equation formulation for the heat equation is also derived and can be used to improve accuracy and stability. The publicly available implementation provides a fast and robust thermophysical model that has been applied to lunar, Martian, and asteroidal surfaces, on occasion to millions of surface facets or parameter combinations.

Keywords: computational methods; planetary surfaces
Submillimeter Observations of Magnetic Fields in Massive Star-forming Region W75N

This paper presents the results of full polarization observations of the massive star-forming region W75N, conducted with ~3″ spatial resolutions at 345 GHz using the Submillimeter Array. The magnetic field structures in the dense cores of the region are derived using the linearly polarized continuum emission. The overall magnetic field strength and orientation are found to agree with those from the previous observations. The plane-of-sky component of the magnetic field in the region was calculated to be ~0.8 ± 0.1 mG using the angular dispersion function method. Further analyses involving the polarization-intensity gradient-local gravity method and H13CO+ (4-3) line data indicated that the cloud is undergoing global gravitational collapse and the magnetic field is shaped by gravity and outflows in the dense core regions.

Keywords: circumstellar matter; interstellar medium; magnetic fields; star formation
Global Mapping of an Exo-Earth Using Sparse Modeling

We develop a new retrieval scheme for obtaining two-dimensional surface maps of exoplanets from scattered light curves. In our scheme, the combination of the L1-norm and total squared variation, which is one of the techniques used in sparse modeling, is adopted to find the optimal map. We apply the new method to simulated scattered light curves of the Earth, and find that the new method provides a better spatial resolution of the reconstructed map than those using Tikhonov regularization. We also apply the new method to observed scattered light curves of the Earth obtained during the two-year Deep Space Climate Observatory/Earth Polychromatic Imaging Camera observations presented by Fan et al. The method with Tikhonov regularization enables us to resolve North America, Africa, Eurasia, and Antarctica. In addition to that, the sparse modeling identifies South America and Australia, although it fails to find Antarctica, maybe due to low observational weights on the poles. Besides, the proposed method is capable of retrieving maps from noise-injected light curves of a hypothetical Earthlike exoplanet at 5 pc with a noise level expected from coronagraphic images from a 8 m space telescope. We find that the sparse modeling resolves Australia, Afro-Eurasia, North America, and South America using 2 yr observation with a time interval of one month. Our study shows that the combination of sparse modeling and multiepoch observation with 1 day or 5 days per month can be used to identify main features of an Earth analog in future direct-imaging missions such as the Large UV/Optical/IR Surveyor.

Keywords: exoplanet astronomy; astrobiology; direct imaging
Constraints on the Bright Meyer Group Comet C/2023 F2 (SOHO)

Comet C/2023 F2 (SOHO) was one of the brightest members of the poorly understood Meyer near-Sun comet group. Here we report our unsuccessful attempt to recover this comet from the ground using the Danish 1.54 m telescope. We observed the predicted position of the comet on 2023 April 4-5 UT when the comet was at 0.6 au and 36°-38° from the Sun, and searched an area that has 5%-10% likelihood to contain the comet down to R ~ 20. Despite the search being unsuccessful, we show that it is possible to reach reasonable depth at small solar elongation, and that wide-field meter-class telescopes are desirable for the recovery of these objects from the ground.

Keywords: comets; near-sun comets; long period comets
A Spectral Method to Compute the Tides of Laterally Heterogeneous Bodies

Body tides reveal information about planetary interiors and affect their evolution. Most models to compute body tides rely on the assumption of a spherically symmetric interior. However, several processes can lead to lateral variations of interior properties. We present a new spectral method to compute the tidal response of laterally heterogeneous bodies. Compared to previous spectral methods, our approach is not limited to small-amplitude lateral variations; compared to finite element codes, this approach is more computationally efficient. While the tidal response of a spherically symmetric body has the same wavelength as the tidal force; lateral heterogeneities produce an additional tidal response with a spectra that depends on the spatial pattern of such variations. For Mercury, the Moon, and Io, the amplitude of this signal is as high as 1%–10% of the main tidal response for long-wavelength shear modulus variations higher than ∼10% of the mean shear modulus. For Europa, Ganymede, and Enceladus, shell-thickness variations of 50% of the mean shell thickness can cause an additional signal of ∼1% and ∼10% for the Jovian moons and Encelaudus, respectively. Future missions, such as BepiColombo and JUICE, might measure these signals. Lateral variations of viscosity affect the distribution of tidal heating. This can drive the thermal evolution of tidally active bodies and affect the distribution of active regions.

Keywords: solid body tides; planetary interior; natural satellites (solar system)
Exploring Spatial and Temporal Patterns in the Debrecen Solar Faculae Database: Part I

Photospheric faculae are markers of the solar magnetic field, appearing as bright regions along the edges of granules on the Sun's surface. Using data from the Debrecen Solar Faculae Database, we investigated the spatiotemporal distribution of photospheric faculae between 2010 May 1 and 2014 December 31 and found the following. (i) At lower latitudes, there is an enhanced abundance of faculae appearing as stripes at given Carrington longitudes, which are interpreted as indicative of the presence of active longitudes. (ii) At higher latitudes, we identified so-called crisscross patterns of facular appearance. These patterns are likely the result of faculae in regions situated along the boundaries of supergranules. Last but not least, (iii) various periods of oscillatory phenomena were identified in this facular data set, including a longer periodic range consistent with the quasi-biennial oscillations and shorter ones with periods of 4–12 days. Our findings are supported by the visualization of a simple heuristic thought experiment and more complex dynamo simulations, strengthening the proposed interpretation of the three observed solar phenomena reported.

Keywords: solar faculae
Kalman Filtering for Tip-tilt Correction in Adaptive Optics

Correcting the tip and tilt modes of optical aberrations can mitigate a large proportion of distortions in adaptive optics (AO) systems. We describe a method to greatly improve tip/tilt correction for the Keck telescopes, using a Kalman filter with a physics model conditioned by the expected tip/tilt power spectrum and vibration peaks. The model builds on similar implementations, such as that of the Gemini Planet Imager, by considering the effects of loop delays, the response of the control hardware, and systematics specific to Keck. We demonstrate improved correction in simulation, and discuss how this model could be tuned to a specific telescope and otherwise improved.

Keywords: astronomical optics
Harmonic Electron Cyclotron Maser Emission along the Coronal Loop

Efficient radiation at second and/or higher harmonics of Ωce has been suggested to circumvent the escaping difficulty of the electron cyclotron maser emission mechanism when it is applied to solar radio bursts, such as spikes. In our earlier study, we developed a three-step numerical scheme to connect the dynamics of energetic electrons within a large-scale coronal loop structure with the microscale kinetic instability energized by the obtained nonthermal velocity distribution and found that direct and efficient harmonic X-mode (X2 for short) emission can be achieved due to the strip-like features of the distribution. That study only considered the radiation from the loop top at a specific time. Here we present the emission properties along the loop at different locations and timings. We found that, in accordance with our earlier results, few to several strip-like features can appear in all cases, and the first two strips play the major role in exciting X2 and Z (i.e., the slow extraordinary mode) that propagate quasi-perpendicularly. For the four sections along the loop, significant excitation of X2 is observed from the upper two sections, and the strongest emission is from the top section. In addition, significant excitation of Z is observed for all loop sections, while there is no significant emission of the fundamental X mode. The study provides new insight into coherent maser emission along the coronal loop structure during solar flares.

Keywords: solar activity; solar corona; radio bursts; solar coronal radio emission
The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters. XXIV. Differences in Internal Kinematics of Multiple Stellar Populations

Our understanding of the kinematic properties of multiple stellar populations (mPOPs) in Galactic globular clusters (GCs) is still limited compared to what we know about their chemical and photometric characteristics. Such limitation arises from the lack of a comprehensive observational investigation of this topic. Here we present the first homogeneous kinematic analysis of mPOPs in 56 GCs based on high-precision proper motions computed with Hubble Space Telescope data. We focused on red-giant-branch stars, for which the mPOP tagging is clearer, and measured the velocity dispersion of stars belonging to first (1G) and second generations (2G). We find that 1G stars are generally kinematically isotropic even at the half-light radius, whereas 2G stars are isotropic at the center and become radially anisotropic before the half-light radius. The radial anisotropy is induced by a lower tangential velocity dispersion of 2G stars with respect to the 1G population, while the radial component of the motion is comparable. We also show possible evidence that the kinematic properties of mPOPs are affected by the Galactic tidal field, corroborating previous observational and theoretical results suggesting a relation between the strength of the external tidal field and some properties of mPOPs. Although limited to the GCs' central regions, our analysis leads to new insights into the mPOP phenomenon, and provides the motivation for future observational studies of the internal kinematics of mPOPs.

Keywords: globular star clusters; proper motions; stellar kinematics
Cosmic Tidal Reconstruction with Halo Fields

The gravitational coupling between large-scale perturbations and small-scale perturbations leads to anisotropic distortions of the small-scale matter distribution. The measured local small-scale power spectrum can thus be used to infer the large-scale matter distribution. In this paper, we present a new tidal reconstruction algorithm for reconstructing large-scale modes using the full three-dimensional tidal shear information. We apply it to simulated dark matter halo fields and find the reconstructed large-scale density field correlates well with the original matter density field on large scales, improving upon the previous tidal reconstruction method, which only uses two transverse shear fields. This has profound implications for recovering lost 21 cm radial modes due to foreground subtraction and constraining primordial non-Gaussianity using the multitracer method with future cosmological surveys.

Keywords: cosmology; n-body simulations; large-scale structure of the universe; dark matter distribution; non-gaussianity; astronomical methods; gravitational interaction
Revisiting the Red Giant Branch Hosts KOI-3886 and ι Draconis. Detailed Asteroseismic Modeling and Consolidated Stellar Parameters

Asteroseismology is playing an increasingly important role in the characterization of red giant host stars and their planetary systems. Here, we conduct detailed asteroseismic modeling of the evolved red giant branch (RGB) hosts KOI-3886 and ι Draconis, making use of end-of-mission Kepler (KOI-3886) and multisector TESS (ι Draconis) time-series photometry. We also model the benchmark star KIC 8410637, a member of an eclipsing binary, thus providing a direct test to the seismic determination. We test the impact of adopting different sets of observed modes as seismic constraints. Inclusion of ℓ = 1 and 2 modes improves the precision of the stellar parameters, albeit marginally, compared to adopting radial modes alone, with 1.9%-3.0% (radius), 5%-9% (mass), and 19%-25% (age) reached when using all p-dominated modes as constraints. Given the very small spacing of adjacent dipole mixed modes in evolved RGB stars, the sparse set of observed g-dominated modes is not able to provide extra constraints, further leading to highly multimodal posteriors. Access to multiyear time-series photometry does not improve matters, with detailed modeling of evolved RGB stars based on (lower-resolution) TESS data sets attaining a precision commensurate with that based on end-of-mission Kepler data. Furthermore, we test the impact of varying the atmospheric boundary condition in our stellar models. We find the mass and radius estimates to be insensitive to the description of the near-surface layers, at the expense of substantially changing both the near-surface structure of the best-fitting models and the values of associated parameters like the initial helium abundance, Y i . Attempts to measure Y i from seismic modeling of red giants may thus be systematically dependent on the choice of atmospheric physics.

Keywords: asteroseismology; stellar evolution; fundamental parameters of stars
Predicting the Yield of Small Transiting Exoplanets around Mid-M and Ultracool Dwarfs in the Nancy Grace Roman Space Telescope Galactic Bulge Time Domain Survey

We simulate the yield of small (0.5-4.0 R ⊕) transiting exoplanets around single mid-M and ultracool dwarfs (UCDs) in the Nancy Grace Roman Space Telescope Galactic Bulge Time Domain Survey. We consider multiple approaches for simulating M3-T9 sources within the survey fields, including scaling local space densities and using Galactic stellar population synthesis models. These approaches independently predict ~100,000 single mid-M dwarfs and UCDs brighter than a Roman F146 magnitude of 21 that are within the survey fields. Assuming planet occurrence statistics previously measured for early-to-mid-M dwarfs, we predict that the survey will discover ${1347}_{-124}^{+208}$ small transiting planets around these sources, each to a significance of 7.1σ or greater. Significant departures from this prediction would test whether the occurrence rates of small planets increase or decrease around mid-M dwarfs and UCDs compared to early-M dwarfs. We predict the detection of ${13}_{-3}^{+4}$ habitable, terrestrial planets (R p < 1.23 R ⊕) in the survey. However, atmospheric characterization of these planets will be challenging with current or near-future space telescope facilities due to the faintness of the host stars. Nevertheless, accurate statistics for the occurrence of small planets around mid-M dwarfs and UCDs will enable direct tests of predictions from planet formation theories and will determine our understanding of planet demographics around the objects at the bottom of the main sequence. This understanding is critical given the prevalence of such objects in our galaxy, whose planets may therefore comprise the bulk of the galactic census of exoplanets.

Keywords: exoplanet astronomy; transit photometry; astronomical simulations; extrasolar rocky planets; surveys; l dwarfs; brown dwarfs; m dwarf stars; late-type dwarf stars; t dwarfs