adsabs/SciX_UAT_keywords huggingface dataset:
New Determinations of the UV Luminosity Functions from z 9 to 2 Show a Remarkable Consistency with Halo Growth and a Constant Star Formation Efficiency

Here we provide the most comprehensive determinations of the rest-frame UV luminosity function (LF) available to date with the Hubble Space Telescope (HST) at z ~ 2-9. Essentially all of the noncluster extragalactic legacy fields are utilized, including the Hubble Ultra Deep Field, the Hubble Frontier Fields parallel fields, and all five CANDELS fields, for a total survey area of 1136 arcmin2. Our determinations include galaxies at z ~ 2-3 leveraging the deep HDUV, UVUDF, and ERS WFC3/UVIS observations available over an ~150 arcmin2 area in the GOODS-North and GOODS-South regions. All together, our collective samples include >24,000 sources, >2.3× larger than previous selections with HST. We identify 5766, 6332, 7240, 3449, 1066, 601, 246, and 33 sources at z ~ 2, 3, 4, 5, 6, 7, 8, and 9, respectively. Combining our results with an earlier z ~ 10 LF determination by Oesch et al., we quantify the evolution of the UV LF. Our results indicate that there is (1) a smooth flattening of the faint-end slope α from α ~ -2.4 at z ~ 10 to α ~ -1.5 at z ~ 2, (2) minimal evolution in the characteristic luminosity M* at z ≥ 2.5, and (3) a monotonic increase in the normalization ${\mathrm{log}}_{10}{\phi }^{* }$ from z ~ 10 to 2, which can be well described by a simple second-order polynomial, consistent with an "accelerated" evolution scenario. We find that each of these trends (from z ~ 10 to 2.5 at least) can be readily explained on the basis of the evolution of the halo mass function and a simple constant star formation efficiency model.

Keywords: lyman-break galaxies; high-redshift galaxies; galaxy evolution; luminosity function
Predicting Solar Flares Using a Novel Deep Convolutional Neural Network

Space weather forecasting is very important, and the prediction of space weather, especially for solar flares, has increasingly attracted research interests with the numerous recent breakthroughs in machine learning. In this study, we propose a novel convolutional neural network (CNN) model to make binary class prediction for both ≥C-class and ≥M-class flares within 24 hr. We collect magnetogram samples of solar active regions (ARs) provided by the Space-weather Helioseismic and Magnetic Imager Active Region Patches (SHARP) data from 2010 May to 2018 September. These samples are used to construct 10 separate data sets. Then, after training, validating, and testing our model, we compare the results of our model with previous studies in several metrics, with a focus on the true skill statistic (TSS). The major results are summarized as follows. (1) We propose a method of shuffle and split cross-validation (CV) based on AR segregation, which is the first attempt to verify the validity and stability of the model in flare prediction. (2) The proposed CNN model achieves a relatively high score of TSS = 0.749 ± 0.079 for ≥M-class prediction, and TSS = 0.679 ± 0.045 for ≥C-class prediction, which is greatly improved compared with previous studies. (3) The model trained on 10 CV data sets is considerably robust and stable in making flare prediction for both ≥C class and ≥M class. Our experimental results indicate that our proposed CNN model is a highly effective method for flare forecasting, with quite excellent prediction performance.

Keywords: convolutional neural networks; magnetic fields; solar activity; solar flares; astronomical techniques
Including Neutrino-driven Convection in the Force Explosion Condition to Predict Explodability of Multidimensional Core-collapse Supernovae (FEC+)

Most massive stars end their lives with core collapse. However, it is not clear which explode as a core-collapse supernova (CCSN), leaving behind a neutron star, and which collapse to a black hole, aborting the explosion. One path to predict explodability without expensive multidimensional simulations is to develop analytic explosion conditions. These analytic conditions also provide a deeper understanding of the explosion mechanism and they provide some insight into why some simulations explode and some do not. The analytic force explosion condition (FEC) reproduces the explosion conditions of spherically symmetric CCSN simulations. In this follow-up manuscript, we include the dominant multidimensional effect that aids explosion—neutrino-driven convection—in the FEC. This generalized critical condition (FEC+) is suitable for multidimensional simulations and has potential to accurately predict explosion conditions of two- and three-dimensional CCSN simulations. We show that adding neutrino-driven convection reduces the critical condition by ∼30%, which is consistent with previous multidimensional simulations.

Keywords: supernovae; core-collapse supernovae; hydrodynamics
Thermal Energy Budget of Electrons in the Inner Heliosphere: Parker Solar Probe Observations

We present an observational analysis of the electron thermal energy budget using data from Parker Solar Probe. We use the macroscopic moments, obtained from our fits to the measured electron distribution function, to evaluate the thermal energy budget based on the second moment of the Boltzmann equation. We separate contributions to the overall budget from reversible and irreversible processes. We find that an irreversible thermal energy source must be present in the inner heliosphere over the heliocentric distance range from 0.15 to 0.47 au. The divergence of the heat flux is positive at heliocentric distances below 0.33 au, while beyond 0.33 au, there is a measurable degradation of the heat flux. Expansion effects dominate the thermal energy budget below 0.3 au. Under our steady-state assumption, the free streaming of the electrons is not sufficient to explain the observed thermal energy density budget. We conjecture that the most likely driver for the required heating process is turbulence. Our results are consistent with the known nonadiabatic polytropic index of the electrons, which we measure as 1.18 in the explored range of heliocentric distances.

Keywords: the sun; solar wind; heliosphere; plasma physics
On the Escape of Low-frequency Waves from Magnetospheres of Neutron Stars

We study the nonlinear decay of the fast magnetosonic (fms) into the Alfvén waves in relativistic force-free magnetohydrodynamics. The work has been motivated by models of pulsar radio emission and fast radio bursts (FRBs), in which the emission is generated in neutron star magnetospheres at conditions when not only the Larmor but also the plasma frequencies significantly exceed the radiation frequency. The decay process places limits on the source luminosity in these models. We estimated the decay rate and showed that the phase volume of Alfvén waves available for the decay of an fms wave is infinite. Therefore, the energy of fms waves could be completely transferred to the small-scale Alfvén waves not via a cascade, as in the Kolmogorov turbulence, but directly. Our results explain the anomalously low radio efficiency of the Crab pulsar and show that FRBs could not be produced well within magnetar magnetospheres.

Keywords: magnetohydrodynamics; plasma astrophysics; radiative processes; pulsars; radio transient sources
Solar Flare Forecast Using 3D Convolutional Neural Networks

Solar flares are immense energy explosions in the solar atmosphere and severely influence space weather. So, forecasting solar flare eruptions is extremely important. Spatial distribution and evolution of active region (AR) magnetic fields are closely related to flare eruptions. In this paper, we simultaneously utilized the two characteristics to build two flare-forecast models using three-dimensional convolutional neural networks (3D CNNs). The two models forecast whether an AR would erupt a ≥C- or ≥M-class flare within the next 24 hr, respectively. The magnetogram sequences provided by the Space-weather Helioseismic and Magnetic Imager Active Region Patches are selected to train our models. We used several performance metrics, such as true skill statistics (TSS), to evaluate our models. The TSS scores of the ≥C and ≥M models reach 0.756 and 0.826, respectively, indicating that our models have superior forecast performance. We used the the gradient-weighted class activation mapping (Grad-CAM) method to visually explain our flare-forecast models. The Grad-CAM illustrates that the 3D CNNs may extract the spatial distribution and evolution of AR magnetic fields simultaneously for flare forecasts. So, the 3D CNN method is valid for flare forecasts, and it utilizes the characteristics related to flare eruptions.

Keywords: solar flares
The Iron Line Profile from Warped Black Hole Accretion Disks

The profile of the fluorescent iron line from black hole accretion disks is a powerful diagnostic of black hole properties, such as spin and inclination. The state of the art, however, considers an accretion disk whose angular momentum is aligned with that of the black hole; this is a very constraining assumption that is unlikely to apply to many astrophysical systems. Here, we present the first simulation of the reflection spectrum from warped accretion disks using a realistic model of the reflected emission based on the XILLVER code. We present the effects that the radial location of the warp and the tilt angle have on the line profile, showing that the affect becomes significant at relatively low angles, between 5° and 15°. We highlight that the results are highly dependent on the azimuth position of the observer relative to the tilt angle. We fit these profiles in XSPEC with the standard relxill lamppost model to quantify the effect that neglecting the disk warps has on the inferred black hole spins and inclinations, finding that the spin parameter can be off by as much as 0.2. We show that fits with two-component relxill can be used to derive more accurate parameter estimates and can recover the radial location of the warp.

Keywords: relativistic disks; black holes; high energy astrophysics; atomic spectroscopy
SCONE: Supernova Classification with a Convolutional Neural Network

We present a novel method of classifying Type Ia supernovae using convolutional neural networks, a neural network framework typically used for image recognition. Our model is trained on photometric information only, eliminating the need for accurate redshift data. Photometric data is preprocessed via 2D Gaussian process regression into two-dimensional images created from flux values at each location in wavelength-time space. These "flux heatmaps" of each supernova detection, along with "uncertainty heatmaps" of the Gaussian process uncertainty, constitute the data set for our model. This preprocessing step not only smooths over irregular sampling rates between filters but also allows SCONE to be independent of the filter set on which it was trained. Our model has achieved impressive performance without redshift on the in-distribution SNIa classification problem: 99.73 ± 0.26% test accuracy with no over/underfitting on a subset of supernovae from PLAsTiCC's unblinded test data set. We have also achieved 98.18 ± 0.3% test accuracy performing six-way classification of supernovae by type. The out-of-distribution performance does not fully match the in-distribution results, suggesting that the detailed characteristics of the training sample in comparison to the test sample have a big impact on the performance. We discuss the implication and directions for future work. All of the data processing and model code developed for this paper can be found in the SCONE software package located at github.com/helenqu/scone.

Keywords: type ia supernovae; classification; convolutional neural networks; supernovae; gaussian processes regression
A Highly Eccentric Warm Jupiter Orbiting TIC 237913194

The orbital parameters of warm Jupiters serve as a record of their formation history, providing constraints on formation scenarios for giant planets on close and intermediate orbits. Here, we report the discovery of TIC 237913194b, detected in full-frame images from Sectors 1 and 2 of the Transiting Exoplanet Survey Satellite (TESS), ground-based photometry (Chilean-Hungarian Automated Telescope, Las Cumbres Observatory Global Telescope), and Fiber-fed Extended Range Optical Spectrograph radial velocity time series. We constrain its mass to ${M}_{P}$ = ${1.942}_{-0.091}^{+0.091}$ ${M}_{J}$ and its radius to ${R}_{{\rm{P}}}$ = ${1.117}_{-0.047}^{+0.054}$ ${R}_{J}$ , implying a bulk density similar to Neptune's. It orbits a G-type star ( ${M}_{\star }$ = ${1.026}_{-0.055}^{+0.057}$ ${M}_{\odot }$ , V = 12.1 mag) with a period of 15.17 days on one of the most eccentric orbits of all known warm giants (e ≈ 0.58). This extreme dynamical state points to a past interaction with an additional, undetected massive companion. A tidal evolution analysis showed a large tidal dissipation timescale, suggesting that the planet is not a progenitor for a hot Jupiter caught during its high-eccentricity migration. TIC 237913194b further represents an attractive opportunity to study the energy deposition and redistribution in the atmosphere of a warm Jupiter with high eccentricity.

Keywords: exoplanet astronomy; transit photometry; radial velocity; exoplanet dynamics; exoplanet atmospheres; exoplanet structure; hot jupiters; extrasolar gaseous giant planets
MALS SALT-NOT Survey of MIR-selected Powerful Radio-bright AGN at 0 < z < 3.5

We present results of an optical spectroscopic survey using SALT and the Nordic Optical Telescope to build a Wide-field Infrared Survey Explorer mid-infrared color-based, dust-unbiased sample of powerful radio-bright (>200 mJy at 1.4 GHz) active galactic nuclei (AGN) for the MeerKAT Absorption Line Survey (MALS). Our sample has 250 AGN (median z = 1.8) showing emission lines, 26 with no emission lines, and 27 without optical counterparts. Overall, our sample is fainter (Δi = 0.6 mag) and redder (Δ(g-i) = 0.2 mag) than radio-selected quasars, and representative of fainter quasar population detected in optical surveys. About 20% of the sources are narrow-line AGN (NLAGN)-65% of these, at z < 0.5 are galaxies without strong nuclear emission, and 10% at z > 1.9, have emission line ratios similar to radio galaxies. The farthest NLAGN in our sample is M1513-2524 (z em = 3.132), and the largest radio source (size ~330 kpc) is M0909-3133 (z em = 0.884). We discuss in detail 110 AGN at 1.9 < z < 3.5. Despite representing the radio loudest quasars (median R = 3685), their Eddington ratios are similar to the Sloan Digital Sky Survey quasars having lower R. We detect four C IV broad-absorption line (BAL) QSOs, all among AGN with least R, and highest black hole masses and Eddington ratios. The BAL detection rate ( ${4}_{-2}^{+3}$ %) is consistent with that seen in extremely powerful (L 1.4GHz > 1025 W Hz-1) quasars. Using optical light curves, radio polarization, and γ-ray detections, we identify seven high-probability BL Lacertae objects. We also summarize the full MALS footprint to search for H I 21 cm and OH 18 cm lines at z < 2.

Keywords: active galactic nuclei; quasars; broad-absorption line quasar; blazars
Multipoint Observations of the Dynamics at an ICME Sheath-Ejecta Boundary

The radial evolution of interplanetary coronal mass ejections (ICMEs) is dependent on their interaction with the ambient medium, which causes ICME erosion and affects their geoefficiency. Here, an ICME front boundary, which separates the confined ejecta from the mixed, interacted sheath-ejecta plasma upstream, is analyzed in a multipoint study examining the ICME at 1 au on 2020 April 20. A bifurcated current sheet, highly filamented currents, and a two-sided jet were observed at the boundary. The two-sided jet, which was recorded for the first time for a magnetic shear angle <40°, implies multiple (patchy) reconnection sites associated with the ICME erosion. The reconnection exhaust exhibited fine structure, including multistep magnetic field rotation and localized structures that were measured only by separate Cluster spacecraft with the mission inter-spacecraft separation of 0.4-1.6 R E. The mixed plasma upstream of the boundary with a precursor at 0.8 au lacked coherency at 1 au and exhibited substantial variations of southward magnetic fields over radial (transverse) distances of 41-237 R E (114 R E). This incoherence demonstrates the need for continuous (sub)second-resolution plasma and field measurements at multiple locations in the solar wind to adequately address the spatiotemporal structure of ICMEs and to produce accurate space weather predictions.

Keywords: solar coronal mass ejections; interplanetary magnetic fields; solar magnetic reconnection; solar wind
First Sagittarius A* Event Horizon Telescope Results. VII. Polarization of the Ring

The Event Horizon Telescope observed the horizon-scale synchrotron emission region around the Galactic center supermassive black hole, Sagittarius A* (Sgr A*), in 2017. These observations revealed a bright, thick ring morphology with a diameter of 51.8 ± 2.3 μas and modest azimuthal brightness asymmetry, consistent with the expected appearance of a black hole with mass M ≈ 4 × 106 M ⊙. From these observations, we present the first resolved linear and circular polarimetric images of Sgr A*. The linear polarization images demonstrate that the emission ring is highly polarized, exhibiting a prominent spiral electric vector polarization angle pattern with a peak fractional polarization of ∼40% in the western portion of the ring. The circular polarization images feature a modestly (∼5%–10%) polarized dipole structure along the emission ring, with negative circular polarization in the western region and positive circular polarization in the eastern region, although our methods exhibit stronger disagreement than for linear polarization. We analyze the data using multiple independent imaging and modeling methods, each of which is validated using a standardized suite of synthetic data sets. While the detailed spatial distribution of the linear polarization along the ring remains uncertain owing to the intrinsic variability of the source, the spiraling polarization structure is robust to methodological choices. The degree and orientation of the linear polarization provide stringent constraints for the black hole and its surrounding magnetic fields, which we discuss in an accompanying publication.

Keywords: black holes; supermassive black holes; polarimetry; radio interferometry; very long baseline interferometry; galactic center
Statistical Study of Small-scale Magnetic Holes in the Upstream Regime of the Martian Bow Shock

Small-scale magnetic holes (SSMHs) are frequently observed in the solar wind at 1 au, as well as the terrestrial current sheet and magnetosheath. These kinetic-size structures play an important role in energy dissipation and particle transportation. Here, we report the existence of SSMHs in the upstream regime of the Martian bow shock and statistically investigate these SSMHs based on 5 yr observations of the Mars Atmosphere and Volatile EvolutioN spacecraft. A total of 549 SSMHs are found, and their durations and sizes obey the lognormal distribution. The median duration is ~0.46 s, and the median size is ~2 ion inertial lengths. We regard an isolated SSMH or a train of SSMHs as a SSMH event. The average occurrence rate of the SSMH events is ~0.6 event per day. The occurrence rate is much larger in the region belonging to the ion foreshock on average, suggesting that the ion foreshock is an important source of SSMHs. The occurrence of the SSMH events tends to be larger when the ion number density and the interplanetary magnetic field (IMF) strength are larger, indicating that the generation of SSMHs might be associated with ions and the IMF strength. Although their generation mechanism is still unclear, the finding of the link between the occurrence rate of the SSMH events and ion number density, as well as the IMF strength, might provide a clue to further reveal the generation mechanism of SSMHs in the solar wind or planetary foreshock.

Keywords: solar wind; solar-planetary interactions; interplanetary magnetic fields
Giant Planets, Tiny Stars: Producing Short-period Planets around White Dwarfs with the Eccentric Kozai-Lidov Mechanism

The recent discoveries of WD J091405.30+191412.25 (WD J0914 hereafter), a white dwarf (WD) likely accreting material from an ice-giant planet, and WD 1856+534 b (WD 1856 b hereafter), a Jupiter-sized planet transiting a WD, are the first direct evidence of giant planets orbiting WDs. However, for both systems, the observations indicate that the planets' current orbital distances would have put them inside the stellar envelope during the red-giant phase, implying that the planets must have migrated to their current orbits after their host stars became WDs. Furthermore, WD J0914 is a very hot WD with a short cooling time that indicates a fast migration mechanism. Here, we demonstrate that the Eccentric Kozai-Lidov Mechanism, combined with stellar evolution and tidal effects, can naturally produce the observed orbital configurations, assuming that the WDs have distant stellar companions. Indeed, WD 1856 is part of a stellar triple system, being a distant companion to a stellar binary. We provide constraints for the orbital and physical characteristics for the potential stellar companion of WD J0914 and determine the initial orbital parameters of the WD 1856 system.

Keywords: white dwarf stars; binary stars; exoplanet dynamics; exoplanet evolution; stellar dynamics; late stellar evolution
A New Reaction Rate of the 27Al(p/α)24Mg Reaction Based on Indirect Measurements at Astrophysical Energies and Implications for 27Al Yields of Intermediate-mass Stars

The abundance of 26Al carries a special role in astrophysics, since it probes active nucleosynthesis in the Milky Way and constrains the Galactic core-collapse supernovae rate. It is estimated through the detection of the 1809 keV γ-line and from the superabundance of 26Mg in comparison with the most abundant Mg isotope (A = 24) in meteorites. For this reason, high precision is necessary also in the investigation of the stable 27Al and 24Mg isotopes. Moreover, these nuclei enter the so-called MgAl cycle, playing an important role in the production of Al and Mg. Recently, high-resolution stellar surveys have shown that the Mg-Al anticorrelation in red-giant stars in globular clusters may hide the existence of multiple stellar populations, and that the relative abundances of Mg isotopes may not be correlated with Al. The common thread running through these astrophysical scenarios is the 27Al(p,α)24Mg reaction, which is the main 27Al destruction channel and directly correlates its abundance with the 24Mg one. Since available reaction rates show large uncertainties owing to the vanishingly small cross section at astrophysical energies, we have applied the Trojan Horse Method to deduce the reaction rate with no need of extrapolation. The indirect measurement made it possible to assess the contribution of the 84 keV resonance and to lower upper limits on the strength of nearby resonances. In intermediate-mass AGB stars experiencing hot bottom burning, a sizeable increase in surface aluminum abundance is observed at the lowest masses, while 24Mg is essentially unaffected by the change in the reaction rate.

Keywords: nuclear abundances; nuclear astrophysics; nucleosynthesis; stellar nucleosynthesis; hydrogen burning; asymptotic giant branch stars