adsabs/SciX_UAT_keywords huggingface dataset:
Spectral Analysis of GRB 220426A: Another Case of a Thermally Dominated Burst

We report a very bright, long-duration gamma-ray burst (GRB), GRB 220426A, observed by the Fermi satellite. GRB 220426A, with a total duration of T 90 = 6 s, is composed of two main pulses and some subpeaks. The spectral analysis of this burst with a Band function reveals that both the time-integrated and the time-resolved spectra are very narrow with a high α ≳ 0.2 and low β ≲ -3.1. It is highly reminiscent of GRB 090902B, a special GRB with a photospheric emission identification. Then, we perform the spectral analysis of this burst based on nondissipated photospheric emission, which can be well modeled by a multicolor blackbody with a cutoff power-law distribution of the thermal temperature. The spectral fittings reveal that the photospheric emission can well describe the radiation spectrum of this burst. We conclude that this burst would be a second burst in the class of GRB 090902B observed by the Fermi satellite. We also discuss the physics of the photosphere and the origin of the high-energy component in GRB 220426A.

Keywords: gamma-ray bursts
Unveiling the Importance of Magnetic Fields in the Evolution of Dense Clumps Formed at the Waist of Bipolar H II Regions: A Case Study of Sh 2-201 with JCMT SCUBA-2/POL-2

We present the properties of magnetic fields (B fields) in two clumps (clump 1 and clump 2), located at the waist of the bipolar H II region Sh 2-201, based on James Clerk Maxwell Telescope SCUBA-2/POL-2 observations of 850 μm polarized dust emission. We find that B fields in the direction of the clumps are bent and compressed, showing bow-like morphologies, which we attribute to the feedback effect of the H II region on the surface of the clumps. Using the modified Davis-Chandrasekhar-Fermi method, we estimate B-field strengths of 266 and 65 μG for clump 1 and clump 2, respectively. From virial analyses and critical mass ratio estimates, we argue that clump 1 is gravitationally bound and could be undergoing collapse, whereas clump 2 is unbound and stable. We hypothesize that the interplay of the thermal pressure imparted by the H II region, the B-field morphologies, and the various internal pressures of the clumps (such as magnetic, turbulent, and gas thermal pressures) has the following consequences: (a) formation of clumps at the waist of the H II region; (b) progressive compression and enhancement of the B fields in the clumps; (c) stronger B fields that will shield the clumps from erosion by the H II region and cause pressure equilibrium between the clumps and the H II region, thereby allowing expanding ionization fronts to blow away from the filament ridge, forming bipolar H II regions; and (d) stronger B fields and turbulence that will be able to stabilize the clumps. A study of a larger sample of bipolar H II regions would help to determine whether our hypotheses are widely applicable.

Keywords: interstellar magnetic fields; submillimeter astronomy; dust continuum emission; star formation; h ii regions; magnetic fields; stellar feedback
A Probabilistic Approach to Kepler Completeness and Reliability for Exoplanet Occurrence Rates

Exoplanet catalogs produced by surveys suffer from a lack of completeness (not every planet is detected) and less than perfect reliability (not every planet in the catalog is a true planet), particularly near the survey's detection limit. Exoplanet occurrence rate studies based on such a catalog must be corrected for completeness and reliability. The final Kepler data release, DR25, features a uniformly vetted planet candidate catalog and data products that facilitate corrections. We present a new probabilistic approach to the characterization of Kepler completeness and reliability, making full use of the Kepler DR25 products. We illustrate the impact of completeness and reliability corrections with a Poisson-likelihood occurrence rate method, using a recent stellar properties catalog that incorporates Gaia stellar radii and essentially uniform treatment of the stellar population. Correcting for reliability has a significant impact: the exoplanet occurrence rate for orbital period and radius within 20% of Earth's around GK dwarf stars, corrected for reliability, is ${0.015}_{-0.007}^{+0.011}$ , whereas not correcting results in ${0.034}_{-0.012}^{+0.018}$ —correcting for reliability reduces this occurrence rate by more than a factor of two. We further show that using Gaia-based versus DR25 stellar properties impacts the same occurrence rate by a factor of two. We critically examine the the DR25 catalog and the assumptions behind our occurrence rate method. We propose several ways in which confidence in both the Kepler catalog and occurrence rate calculations can be improved. This work provides an example of how the community can use the DR25 completeness and reliability products.

Keywords: exoplanet catalogs; exoplanets; exoplanet detection methods
Star Formation and AGN Activity 500 Myr after the Big Bang: Insights from JWST

We consider the effect of including an active galactic nuclei (AGN) component when fitting spectral energy distributions of 109 spectroscopically confirmed z ≈ 3.5-12.5 galaxies with JWST. Remarkably, we find that the resulting cosmic star formation history is ≈0.4 dex lower at z ≳ 9.5 when an AGN component is included in the fitting. This alleviates previously reported excess star formation at z ≳ 9.5 compared to models based on typical baryon conversion efficiencies inside dark matter halos. We find that the individual stellar masses and star formation rates can be as much as ≈4 dex lower when fitting with an AGN component. These results highlight the importance of considering both stellar mass assembly and supermassive black hole growth when interpreting the light distributions of among the first galaxies to ever exist.

Keywords: high-redshift galaxies; quasars; supermassive black holes; active galactic nuclei
Multiband Polarimetric Imaging of HR 4796A with the Gemini Planet Imager

HR4796A hosts a well-studied debris disk with a long history due to its high fractional luminosity and favorable inclination, which facilitate both unresolved and resolved observations. We present new J- and K1-band images of the resolved debris disk HR4796A taken in the polarimetric mode of the Gemini Planet Imager (GPI). The polarized intensity features a strongly forward-scattered brightness distribution and is undetected at the far side of the disk. The total intensity is detected at all scattering angles and also exhibits a strong forward-scattering peak. We use a forward-modeled geometric disk in order to extract geometric parameters, polarized fraction, and total intensity scattering phase functions for these data as well as H-band data previously taken by GPI. We find the polarized phase function becomes increasingly more forward-scattering as wavelength increases. We fit Mie and distribution of hollow spheres (DHS) grain models to the extracted functions. We find that it is possible to generate a satisfactory model for the total intensity using a DHS model, but not with a Mie model. We find that no single grain population of DHS or Mie grains of arbitrary composition can simultaneously reproduce the polarized fraction and total intensity scattering phase functions, indicating the need for more sophisticated grain models.

Keywords: debris disks; circumstellar disks; circumstellar dust; polarimetry; near infrared astronomy; coronagraphic imaging
The Roles of Mass and Environment in the Quenching of Galaxies. II.

We take advantage of an analytic model of galaxy formation coupled to the merger tree of an N-body simulation to study the roles of environment and stellar mass in the quenching of galaxies. The model has been originally set in order to provide the observed evolution of the stellar mass function as well as reasonable predictions of the star formation rate-stellar mass relation, from high redshift to the present time. We analyze the stellar mass and environmental quenching efficiencies and their dependence on stellar mass, halo mass (taken as a proxy for the environment), and redshift. Our analysis shows that the two quenching efficiencies are dependent on redshift and stellar and halo mass, and that the halo mass is also a good proxy for the environment. The environmental quenching increases with decreasing redshift and is inefficient below log M* ∼ 9.5, reaches the maximum value at log M* ∼ 10.5, and decreases again, becoming poorly efficient at very high stellar mass (log M* ≳ 11.5). Central and satellites galaxies are mass quenched differently: for the former, the quenching efficiency depends very weakly on redshift but strongly on stellar mass; for the latter, it strongly depends on both stellar mass and redshift in the range $10\lesssim \mathrm{log}{M}_{* }\lesssim 11$ . According to the most recent observational results, we find that the two quenching efficiencies are not separable: intermediate-mass galaxies, as well as intermediate/massive galaxies in more massive halos, are environmentally quenched faster. At stellar masses lower than log M* ≲ 9.5, both quenching mechanisms become inefficient, independently of the redshift.

Keywords: galaxy formation; galaxy evolution
Energy Partition of Thermal and Nonthermal Particles in Magnetic Reconnection

Magnetic reconnection has long been known to be the most important mechanism for quick conversion of magnetic field energy into plasma kinetic energy. In addition, energy dissipation by reconnection has gained attention not only as a plasma heating mechanism, but also as a plasma mechanism for accelerating nonthermal particles. However, the energy partitioning of thermal and nonthermal plasmas during magnetic reconnection is not understood. Here, we studied energy partition as a function of plasma sheet temperature and guide magnetic field. In relativistic reconnection with an antiparallel magnetic field or a weak guide magnetic field, it was found that the nonthermal energy density can occupy more than 90% of the total kinetic plasma energy density, but strengthening the guide magnetic field suppresses the efficiency of the nonthermal particle acceleration. In nonrelativistic reconnection for an antiparallel magnetic field, most dissipated magnetic field energy is converted into thermal plasma heating. For a weak guide magnetic field with a moderate value, however, the nonthermal particle acceleration efficiency was enhanced, but strengthening the guide field beyond the moderate value suppresses the efficiency.

Keywords: plasma astrophysics; plasma physics; solar magnetic reconnection; astronomical simulations; pulsar wind nebulae; magnetars; pulsars; space plasmas
Discovery of the Optical Afterglow and Host Galaxy of Short GRB 181123B at z = 1.754: Implications for Delay Time Distributions

We present the discovery of the optical afterglow and host galaxy of the Swift short-duration gamma-ray burst (SGRB) GRB 181123B. Observations with Gemini-North starting ≈9.1 hr after the burst reveal a faint optical afterglow with i ≈ 25.1 mag at an angular offset of 0"59 ± 0"16 from its host galaxy. Using grizYJHK observations, we measure a photometric redshift of the host galaxy of $z={1.77}_{-0.17}^{+0.30}$ . From a combination of Gemini and Keck spectroscopy of the host galaxy spanning 4500-18000 Å, we detect a single emission line at 13390 Å, inferred as Hβ at z = 1.754 ± 0.001 and corroborating the photometric redshift. The host galaxy properties of GRB 181123B are typical of those of other SGRB hosts, with an inferred stellar mass of ≈9.1 × 109 M⊙, a mass-weighted age of ≈0.9 Gyr, and an optical luminosity of ≈0.9L*. At z = 1.754, GRB 181123B is the most distant secure SGRB with an optical afterglow detection and one of only three at z > 1.5. Motivated by a growing number of high-z SGRBs, we explore the effects of a missing z > 1.5 SGRB population among the current Swift sample on delay time distribution (DTD) models. We find that lognormal models with mean delay times of ≈4-6 Gyr are consistent with the observed distribution but can be ruled out to 95% confidence, with an additional ≈one to five Swift SGRBs recovered at z > 1.5. In contrast, power-law models with ∝t-1 are consistent with the redshift distribution and can accommodate up to ≈30 SGRBs at these redshifts. Under this model, we predict that ≈1/3 of the current Swift population of SGRBs is at z > 1. The future discovery or recovery of existing high-z SGRBs will provide significant discriminating power on their DTDs and thus their formation channels.

Keywords: gamma-ray bursts
One Solar Cycle of Heliosphere Observations with the Interstellar Boundary Explorer: Energetic Neutral Hydrogen Atoms Observed with IBEX-Lo from 10 eV to 2 keV

The Interstellar Boundary Explorer (IBEX) is a NASA satellite in Earth orbit, dedicated to observing both interstellar neutral atoms entering the heliosphere and energetic neutral atoms (ENAs) from the interstellar boundaries from roughly 10 eV to 6 keV. This work presents the averaged maps, energy spectra, and temporal variability of heliospheric ENA intensities measured with the IBEX-Lo instrument at 1 au at energies between 10 eV and 2 keV, covering one entire solar cycle from 2009 through 2019. These results expand the range in time and energy for studying the globally distributed ENA flux and the IBEX Ribbon. The observed ENA intensities exceed model predictions, in particular below 500 eV. Moreover, the ENA intensities between 50-200 eV energy show an unexpected rise and fall around the year 2015 in most sky regions.

Keywords: heliosphere; heliosheath
Masers and Star Formation Activities in W51A

Concurrently with the maser flare observed in W51-North during the 3 month monitoring of H2O, NH3, and CH3OH maser variability from 2020 January to April using the Tianma 65 m Radio Telescope, we conducted Very Large Array mappings for these three maser species across the entirety of W51A region. After finding the ring-shaped H2O maser which might trace the disk surrounding the protostar residing in W51-North, the NH3 (9,6) maser delineated a jet which might be illuminated in the luminosity outburst possibly caused by the infalling streamer's interaction with the protostar's disk. An analysis of the comprehensive distribution of maser spots allowed us to affirm that W51N4 or ALMAmm31 serves as the primary source of the Lacy jet. Furthermore, we observed that class I methanol maser spots may extend beyond the locations of the H2O and NH3 (9,6) masers within the outflow. Additionally, emissions from other NH3 maser transitions coincided with specific 1.3 mm continuum sources. The arrangement of H2O maser spots in the vicinity of W51e2-E potentially indicates episodic accretions in this source. Combining the data from the Atacama Large Millimeter/submillimeter Array data archive for W51-North, W51e2, and W51e8, we have discovered that the H2O, NH3, and CH3OH masers, as well as the HC3N and SiO emissions are found to be good tools for tracing outflow in this work for W51A.

Keywords: star formation; interstellar masers; astrophysical masers; young stellar objects; protostars
Discovery of a Radio-loud Narrow-line Seyfert 1 Galaxy at z = 0.9 Reddened with a Strong 2175 Å Bump

We present a broadband spectrophotometric analysis of an unusual quasar, SDSS J160558.86+474300.1, at z = 0.9, found in a systematic search for reddened radio-loud narrow-line Seyfert 1 galaxies (NLS1s). J1605+4743 qualifies for the conventional definition of an NLS1 in its permitted emission line widths and Hβ/[O III] flux ratio. It also shows strong Fe II emissions. J1605+4743 has a steep radio spectrum. With a radio loudness of ~150 (70) before (after) reddening correction, it is among the most radio-loud NLS1s discovered. In addition, the blueshifted emission lines are also found to be weak, suggesting that it can be an exotic "wind-dominated" Seyfert similar to weak-line quasars, especially the ones with strong reddening. As an extreme hybrid central engine, its environment and host galaxy become rather intriguing. We discover in it a proximate 2175 Å absorber with a bump strength similar to the average value of 2175 Å absorbers in the Milky Way, which we suspect can be intrinsic to the quasar. In addition, the quasar seems to have enhanced instead of suppressed star formation at a rate of ≳94 M ⊙ yr-1. The combination of these unusual properties, i.e., the unique extinction, strong Fe II and [O II] lines, weak [O III], Mg II, and Balmer lines, and large radio loudness, might hold important clues to accretion physics, the formation/destruction of dust grains in the environment of active galactic nuclei, and possibly also the coevolution of supermassive black holes and their host galaxies in general.

Keywords: active galaxies; emission line galaxies; quasar absorption line spectroscopy; extinction; radio active galactic nuclei
Revisiting Rotation Measures from the Canadian Galactic Plane Survey: the Magnetic Field in the Disk of the Outer Galaxy

Faraday rotation provides a valuable tracer of magnetic fields in the interstellar medium; catalogs of Faraday rotation measures provide key observations for studies of the Galactic magnetic field. We present a new catalog of rotation measures derived from the Canadian Galactic Plane Survey, covering a large region of the Galactic plane spanning 52° < l < 192°, -3° < b < 5°, along with northern and southern latitude extensions around l ≈ 105°. We have derived rotation measures for 2234 sources (4 of which are known pulsars), 75% of which have no previous measurements, over an area of approximately 1300 deg2. These new rotation measures increase the measurement density for this region of the Galactic plane by a factor of 2.

Keywords: catalogs; milky way magnetic fields; polarimetry
Mind the Gap. I. Hα Activity of M Dwarfs Near the Partially/Fully Convective Boundary and a New Hα Emission Deficiency Zone on the Main Sequence

Since identifying the gap in the H-R Diagram (HRD) marking the transition between partially and fully-convective interiors, a unique type of slowly pulsating M dwarf has been proposed. These unstable M dwarfs provide new laboratories in which to understand how changing interior structures can produce potentially observable activity at the surface. In this work, we report the results of the largest high-resolution spectroscopic Hα emission survey to date spanning this transition region, including 480 M dwarfs observed using the CHIRON spectrograph at CTIO/SMARTS 1.5 m. We find that M dwarfs with Hα in emission are almost entirely found 0-0.5 mag above the top edge of the gap in the HRD, whereas effectively no stars in and below the gap show emission. Thus, the top edge of the gap marks a relatively sharp activity transition, and there is no anomalous Hα activity for stars in the gap. We also identify a new region at 10.3 < M G < 10.8 on the main sequence where fewer M dwarfs exhibit Hα emission compared to M dwarfs above and below this magnitude range. Careful evaluation of the results in the literature indicates that (1) rotation and Hα activity distributions on the main-sequence are closely related, and (2) fewer stars in this absolute magnitude range rotate in less than ~13 days than populations surrounding this region. This result suggests that the most massive fully-convective stars lose their angular momentum faster than both partially convective stars and less massive fully-convective stars.

Keywords: hertzsprung russell diagram; m dwarf stars; stellar activity; stellar rotation; high resolution spectroscopy
Introducing the Search for Intermediate-mass Black Holes in Nearby Galaxies (SIBLING) Survey

Intermediate-mass black holes (IMBHs) have masses between 102 and 106 M⊙ and are key to our understanding of the formation of massive black holes. The known population of IMBHs remains small, with a few hundred candidates and only a handful of them confirmed as bona fide IMBHs. Until now, the most widely used selection method is based on spectral analysis. Here we present a methodology to select IMBH candidates via optical variability analysis of the nuclear region of local galaxies ( $z\leqslant 0.35$ ). Active IMBHs accreting at low rates show small amplitude variability with timescales of hours, as is seen in one of the known IMBHs, NGC 4395. We found a sample of ∼500 galaxies demonstrating fast and small amplitude variation in their week-based light curves. We estimate an average occupancy fraction of 4% and a surface density of ∼3 deg-2, which represent an increase by a factor of ∼40 compared to previous searches. A large fraction (78%) of the candidates are in spiral galaxies. We preliminarily confirm the active galactic nucleus nature of 22 sources via Baldwin, Phillips, and Terlevich diagrams using Sloan Digital Sky Survey legacy spectra. Further confirmation of these candidates will require multiwavelength observations, especially in X-ray and radio bands.

Keywords: surveys; active galaxies; galaxies; agn host galaxies; intermediate-mass black holes; galaxy counts
Learning How to Surf: Reconstructing the Propagation and Origin of Gravitational Waves with Gaussian Processes

Soon, the combination of electromagnetic and gravitational signals will open the door to a new era of gravitational-wave (GW) cosmology. It will allow us to test the propagation of tensor perturbations across cosmic time and study the distribution of their sources over large scales. In this work, we show how machine-learning techniques can be used to reconstruct new physics by leveraging the spatial correlation between GW mergers and galaxies. We explore the possibility of jointly reconstructing the modified GW propagation law and the linear bias of GW sources, as well as breaking the slight degeneracy between them by combining multiple techniques. We show predictions roughly based on a network of Einstein Telescopes combined with a high-redshift galaxy survey (z ≲ 3). Moreover, we investigate how these results can be rescaled to other instrumental configurations. In the long run, we find that obtaining accurate and precise luminosity distance measurements (extracted directly from the individual GW signals) will be the most important factor to consider when maximizing the constraining power.

Keywords: gravitational wave astronomy; large-scale structure of the universe; gaussian processes regression; non-standard theories of gravity
Background Contamination of the Project Hephaistos Dyson Spheres Candidates

Project Hephaistos recently identified seven M-dwarfs as possible Dyson Spheres (DS) candidates. We have cross-matched three of these candidates (A, B and G) with radio sources detected in various all-sky surveys. The radio sources are offset from the Gaia stellar positions by ∼4.9, ∼0.4 and ∼5.″0 for candidates A, B, and G respectively. We propose that Dust obscured galaxies (DOGs) lying close to the line-of-sight of these M-dwarf stars significantly contribute to the measured WISE mid-IR flux densities in the WISE W3 and W4 wave bands. These three stars have therefore been misidentified as DS candidates. We also note that with an areal sky density of 9 × 10‑6 per square arcsecond, Hot DOGs can probably account for the contamination of all 7 DS candidates drawn from an original sample of 5 million stars.

Keywords: search for extraterrestrial intelligence; extragalactic radio sources; technosignatures; infrared sources