adsabs/SciX_UAT_keywords huggingface dataset:
The Population of H II Regions in NGC 7020

The galaxy NGC 7020 displays an exotic hexagonal ringlike central structure with conspicuous ansae located at two opposite vertices and a tenuous external ring populated by H II regions. Inside and around the hexagonal structure, Hα emission is also present at the inner disk. To characterize the population of the H II regions, as well as their ionizing clusters, we imaged NGC 7020 with narrowband Hα and nearby continuum filters attached to GMOS-S installed on the Gemini South telescope. We found 202 H II regions or complexes of H II regions evenly distributed between the outer ring and the central disk The nucleus and ansae also present Hα emission. The equivalent width of the Hα line (WHα) is systematically greater at the regions of the outer ring relative to those of the inner disk. We discuss the influence of the metallicity gradient of the disk and the upper limit of the masses of the initial mass function on WHα, and we conclude that the data are still consistent with the occurrence of a younger burst of H II region formation in the outer ring. The central regions present more massive clusters, M ≥ 106 M⊙, than those of the outer ring (M ≤ 106 M⊙). Three clusters within 5″ of the nucleus present masses higher than 108 M⊙. The presence of diffuse Hα emission in the inner 5″ suggests gas flows in the nuclear region.

Keywords: galaxies; galaxy nuclei; h ii regions; barred spiral galaxies; narrow band photometry
Properties of Globular Clusters in Galaxy Clusters: Sensitivity from the Formation and Evolution of Globular Clusters

We investigate the properties of globular clusters (GCs) in a galaxy cluster, using the particle tagging method with a semianalytical approach in a cosmological context. We assume GCs form from dark matter halo mergers and their metallicity is assigned based on the stellar mass of the host dark matter halos and the formation redshift of GCs. Dynamical evolution and disruption of GCs are considered using semianalytical approaches, controlled by several free parameters. In this paper, we investigate how our results are changed by the choice of free parameters. We compare our fiducial results with representative observations, including the mass ratio between the GC system and its host galaxy, the GC occupancy, the number fraction of blue GCs, and the metallicity gradient with the GC mass. Because we can know the positions of GCs with time, comparison with additional observations is possible, e.g., the median radii of the GC system in individual galaxies, the mean projected density profiles of intracluster GCs, and the metallicity and age gradients of GCs with a clustercentric radius. We also find that the specific mass of the GC system in each galaxy is different with a clustercentric radius.

Keywords: galaxy clusters; galaxy formation; globular star clusters; computational astronomy
Constraints from Gravitational-wave Detections of Binary Black Hole Mergers on the 12C(α, γ)16O Rate

Gravitational-wave detections are starting to allow us to probe the physical processes in the evolution of very massive stars through the imprints they leave on their final remnants. Stellar evolution theory predicts the existence of a gap in the black hole mass distribution at high mass due to the effects of pair instability. Previously, we showed that the location of the gap is robust against model uncertainties, but it does depend sensitively on the uncertain ${}^{12}{\rm{C}}{(\alpha ,\gamma )}^{16}{\rm{O}}$ rate. This rate is of great astrophysical significance and governs the production of oxygen at the expense of carbon. We use the open-source MESA stellar evolution code to evolve massive helium stars to probe the location of the mass gap. We find that the maximum black hole mass below the gap varies between $40\,{M}_{\odot }$ and $90\,{M}_{\odot }$ , depending on the strength of the uncertain ${}^{12}{\rm{C}}{(\alpha ,\gamma )}^{16}{\rm{O}}$ reaction rate. With the first 10 gravitational-wave detections of black holes, we constrain the astrophysical S-factor for ${}^{12}{\rm{C}}{(\alpha ,\gamma )}^{16}{\rm{O}}$ , at $300\,\mathrm{keV}$ , to ${S}_{300}\gt 175\,\,{\rm{keV}}\,{\rm{b}}$ at 68% confidence. With ${ \mathcal O }(50)$ detected binary black hole mergers, we expect to constrain the S-factor to within ±10-30 ${\rm{keV}}\,{\rm{b}}$ . We also highlight a role for independent constraints from electromagnetic transient surveys. The unambiguous detection of pulsational pair-instability supernovae would imply that ${S}_{300}\gt 79\,{\rm{keV}}\,{\rm{b}}$ . Degeneracies with other model uncertainties need to be investigated further, but probing nuclear stellar astrophysics poses a promising science case for the future gravitational-wave detectors.

Keywords: stellar evolution; supernovae; core-collapse supernovae; nuclear astrophysics; stellar mass black holes; astrophysical black holes; massive stars; late stellar evolution
Hubble WFC3 Spectroscopy of the Rocky Planet L 98-59 b: No Evidence for a Cloud-free Primordial Atmosphere

We are using archived data from HST of transiting exoplanet L 98-59 b to place constraints on its potentially hot atmosphere. We analyze the data from five transit visits and extract the final combined transmission spectrum using Iraclis. Then we use the inverse atmospheric retrieval code TauREx to analyze the combined transmission spectrum. There is a weak absorption feature near 1.40 μm and 1.55 μm in the transmission spectrum, which can be modeled by a cloudy atmosphere with abundant hydrogen cyanide (HCN). However, the unrealistically high abundance of HCN derived cannot be explained by any equilibrium chemical model with reasonable assumptions. Thus, the likeliest scenario is that L 98-59 b has a flat, featureless transmission spectrum in the WFC3/G141 bandpass due to a thin atmosphere with high mean molecular weight, an atmosphere with an opaque aerosol layer, or no atmosphere, and it is very unlikely for L 98-59 b to have a clear hydrogen-dominated primary atmosphere. Due to the narrow wavelength coverage and low spectral resolution of HST/WFC3 G141 grism observation, we cannot tell these different scenarios apart. Our simulation shows future higher precision measurements over wider wavelengths from the James Webb Space Telescope can be used to better characterize the planetary atmosphere of L 98-59 b.

Keywords: exoplanet atmospheres; exoplanet atmospheric composition; exoplanets; hubble space telescope; extrasolar rocky planets
Improving the X-Ray Energy Resolution of a Scientific CMOS Detector by Pixel-level Gain Correction

Scientific Complementary Metal Oxide Semiconductor (sCMOS) sensors are finding increasingly more applications in astronomical observations, thanks to their advantages over charge-coupled devices such as a higher readout frame rate, higher radiation tolerance, and higher working temperature. In this work, we investigate the performance at the individual pixel level of a large-format sCMOS sensor, GSENSE1516BSI, which has 4096 × 4096 pixels, each of 15 μm in size. To achieve this, three areas on the sCMOS sensor, each consisting of 99 × 99 pixels, are chosen for the experiment. The readout noise, conversion gain and energy resolutions of the individual pixels in these areas are measured from a large number (more than 25,000) of X-ray events accumulated for each of the pixels through long time exposures. The energy resolution of these pixels can reach 140 eV at 6.4 keV at room temperature and shows a significant positive correlation with the readout noise. The accurate gain can also be derived individually for each of the pixels from its X-ray spectrum obtained. Variations of the gain values are found at a level of 0.56% statistically among the 30 thousand pixels in the areas studied. With the gain of each pixel determined accurately, a precise gain correction is performed pixel by pixel in these areas, in contrast to the standardized ensemble gain used in the conventional method. In this way, we could almost completely eliminate the degradation of energy resolutions caused by gain variations among pixels. As a result, the energy resolution at room temperature can be significantly improved to 124.6 eV at 4.5 keV and 140.7 eV at 6.4 keV. This pixel-by-pixel gain correction method can be applied to all kinds of CMOS sensors, and is expected to find interesting applications in X-ray spectroscopic observations in the future.

Keywords: x-ray detectors; astronomical instrumentation; astronomical detectors
High Equivalent Width of Hα+[N II] Emission in z 8 Lyman-break Galaxies from IRAC 5.8 μm Observations: Evidence for Efficient Lyman-continuum Photon Production in the Epoch of Reionization

We measure, for the first time, the median equivalent width (EW) of Hα+[N II] in star-forming galaxies at z ~ 8. Our estimate leverages the unique photometric depth of the Spitzer/IRAC 5.8 μm band mosaics (probing ≈5500-7100 Å at z ~ 8) of the GOODS Reionization Era Wide Area Treasury from Spitzer (GREATS) program. We median-stacked the stamps of 102 Lyman-break galaxies in the 3.6, 4.5, 5.8, and 8.0 μm bands, after carefully removing potential contamination from neighboring sources. We infer an extreme rest-frame EW0(Hα+[N II]) = ${2328}_{-1127}^{+1326}$ Å from the measured red [3.6] - [5.8] = 0.82 ± 0.27 mag, consistent with young (≲107 yr) average stellar population ages at z ~ 8. This implies an ionizing photon production efficiency of ${\rm{l}}{\rm{o}}{\rm{g}}({\xi }_{{\rm{i}}{\rm{o}}{\rm{n}},0}/{\rm{e}}{\rm{r}}{\rm{g}}\,{{\rm{H}}{\rm{z}}}^{-1})={25.97}_{-0.28}^{+0.18}$ . Such a high value for photoproduction, similar to the highest values found at z ≲ 4, indicates that only modest escape fractions f esc ≲ 0.3 (at 2σ) are sufficient for galaxies brighter than M UV < -18 mag to reionize the neutral hydrogen at z ~ 8. This requirement is relaxed even more to f esc ≤ 0.1 when considering galaxies brighter than M UV ≈ -13 mag, consistent with recent luminosity functions and as typically assumed in studies addressing reionization. These exceptional results clearly indicate that galaxies can be the dominant source of reionizing photons, and provide us with an exciting glimpse into what we might soon learn about the early universe, and particularly about the reionization epoch, from forthcoming JWST/MIRI and NIRCam programs.

Keywords: reionization; lyman-break galaxies; high-redshift galaxies; h alpha photometry; early universe
Developing a Drift Rate Distribution for Technosignature Searches of Exoplanets

A stable-frequency transmitter with relative radial acceleration to a receiver will show a change in received frequency over time, known as a "drift rate." For a transmission from an exoplanet, we must account for multiple components of drift rate: the exoplanet's orbit and rotation, the Earth's orbit and rotation, and other contributions. Understanding the drift rate distribution produced by exoplanets relative to Earth, can (a) help us constrain the range of drift rates to check in a Search for Extraterrestrial Intelligence project to detect radio technosignatures, and (b) help us decide validity of signals-of-interest, as we can compare drifting signals with expected drift rates from the target star. In this paper, we modeled the drift rate distribution for ~5300 confirmed exoplanets, using parameters from the NASA Exoplanet Archive (NEA). We find that confirmed exoplanets have drift rates such that 99% of them fall within the ±53 nHz range. This implies a distribution-informed maximum drift rate ~4 times lower than previous work. To mitigate the observational biases inherent in the NEA, we also simulated an exoplanet population built to reduce these biases. The results suggest that, for a Kepler-like target star without known exoplanets, ±0.44 nHz would be sufficient to account for 99% of signals. This reduction in recommended maximum drift rate is partially due to inclination effects and bias toward short orbital periods in the NEA. These narrowed drift rate maxima will increase the efficiency of searches and save significant computational effort in future radio technosignature searches.

Keywords: search for extraterrestrial intelligence; astrobiology; technosignatures; radio astronomy; exoplanets
Gravitational Redshift for Wide Binaries in Gaia eDR3

The Doppler effect is commonly used to infer the velocity difference between stars based on the relative shifts in the rest-frame wavelengths of their spectral features. In wide binaries, the difference in gravitational redshift from the surfaces of the constituent stars with distinct compactness dominates at separations ≳10-2 pc. I suggest that this effect became apparent for wide pairs in the Gaia eDR3 catalog but was incorrectly interpreted as a possible modification of Newtonian gravity in the internal kinematics of very wide binaries.

Keywords: binary stars
Redshift Evolution of the Feedback-Cooling Equilibrium in the Core of 48 SPT Galaxy Clusters: A Joint Chandra-SPT-ATCA Analysis

We analyze the cooling and feedback properties of 48 galaxy clusters at redshifts 0.4 < z < 1.3 selected from the South Pole Telescope (SPT) catalogs to evolve like the progenitors of massive and well-studied systems at z ~ 0. We estimate the radio power at the brightest cluster galaxy (BCG) location of each cluster from an analysis of Australia Telescope Compact Array data. Assuming that the scaling relation between the radio power and active galactic nucleus (AGN) cavity power P cav observed at low redshift does not evolve with redshift, we use these measurements in order to estimate the expected AGN cavity power in the core of each system. We estimate the X-ray luminosity within the cooling radius L cool of each cluster from a joint analysis of the available Chandra X-ray and SPT Sunyaev-Zel'dovich (SZ) data. This allows us to characterize the redshift evolution of the P cav/L cool ratio. When combined with low-redshift results, these constraints enable investigations of the properties of the feedback-cooling cycle across 9 Gyr of cluster growth. We model the redshift evolution of this ratio measured for cool-core clusters by a log-normal distribution $\mathrm{Log}$ - ${ \mathcal N }(\alpha +\beta z,{\sigma }^{2})$ and constrain the slope of the mean evolution to β = -0.05 ± 0.47. This analysis improves the constraints on the slope of this relation by a factor of two. We find no evidence of redshift evolution of the feedback-cooling equilibrium in these clusters, which suggests that the onset of radio-mode feedback took place at an early stage of cluster formation. High values of P cav/L cool are found at the BCG location of noncool-core clusters, which might suggest that the timescales of the AGN feedback cycle and the cool core-noncool core transition are different. This work demonstrates that the joint analysis of radio, SZ, and X-ray data solidifies the investigation of AGN feedback at high redshifts.

Keywords: galaxy clusters; active galactic nuclei; x-ray astronomy; sunyaev-zeldovich effect; radio active galactic nuclei
300: An ACA 870 μm Continuum Survey of Orion Protostars and Their Evolution

We present an 870 μm continuum survey of 300 protostars from the Herschel Orion Protostar Survey using the Atacama Compact Array (ACA). These data measure protostellar flux densities on envelope scales ≤8000 au (20″) and resolve the structure of envelopes with 1600 au (4″) resolution, a factor of 3-5 improvement in angular resolution over existing single-dish 870 μm observations. We compare the ACA observations to Atacama Large Millimeter/submillimeter Array 12 m array observations at 870 μm with ~0.″1 (40 au) resolution. Using the 12 m data to measure the fluxes from disks and the ACA data within 2500 au to measure the combined disk plus envelope fluxes, we calculate the 12 m/ACA 870 μm flux ratios. Our sample shows a clear evolution in this ratio. Class 0 protostars are mostly envelope-dominated with ratios <0.5. In contrast, Flat Spectrum protostars are primarily disk-dominated with ratios near 1, although with a number of face-on protostars dominated by their envelopes. Class I protostars span the range from envelope to disk-dominated. The increase in ratio is accompanied by a decrease in the envelope fluxes and estimated mass infall rates. We estimate that 80% of the mass is accreted during the envelope-dominated phase. We find that the 12 m/ACA flux ratio is an evolutionary indicator that largely avoids the inclination and foreground extinction dependence of spectral energy distribution-based indicators.

Keywords: protostars; young stellar objects; star formation
Dynamics of Colombo's Top: Generating Exoplanet Obliquities from Planet-Disk Interactions

Large planetary spin-orbit misalignments (obliquities) may strongly influence atmospheric circulation and tidal heating in a planet. A promising avenue to generate obliquities is via spin-orbit resonances, where the spin and orbital precession frequencies of a planet cross each other as the system evolves in time. One such mechanism involves a dissipating (mass-losing) protoplanetary disk that drives orbital precession of an interior planet. We study this scenario analytically in this paper, and obtain the mapping between the general initial spin orientation and the final obliquity. We show that (i) under adiabatic evolution (i.e., the disk dissipates at a sufficiently slow rate), the final planetary obliquity as a function of the initial spin orientation bifurcates into distinct tracks governed by interactions with the resonance; and (ii) under nonadiabatic evolution, a broad range of obliquities can be excited. We obtain analytical expressions for the final obliquities for various regimes of parameter space. The dynamical system studied in this paper is an example of "Colombo's top," and our analysis and results can be adapted to other applications.

Keywords: exoplanet dynamics
Boundary Conditions at the Heliospheric Termination Shock with Pickup Ions

In a collisionless shock the directed flow energy is converted mainly in thermal energy of the plasma species. At the termination shock (TS) a substantial portion of energy goes into heating of pickup ions (PUIs), while heating of the solar wind protons (SW) is weaker than it would be without PUI. Heating of both species is nonadiabatic. Downstream pressure of the mixture is determined by conservation laws for the whole mixture. SW heating is sensitive to the details of the shock front, while heating of PUI is not. The profile is an analytical approximation of the observed TS. Here the downstream temperature and pressure of PUIs are obtained for the first time using test particle analysis in a model shock profile for various magnetic compression ratios and shock angles. The profile is an analytical approximation of the observed TS. The results of the analysis are used in the pressure balance equation and the corresponding SW heating is estimated. The analysis is supported by full particle simulations, except for the SW heating that was not studied using test particle data due to its apparent dependence on fine structure of the shock front.

Keywords: shocks; termination shock; interplanetary shocks; heliosphere
Acceleration and Spectral Redistribution of Cosmic Rays in Radio-jet Shear Flows

A steady-state, semi-analytical model of energetic particle acceleration in radio-jet shear flows due to cosmic-ray viscosity obtained by Webb et al. is generalized to take into account more general cosmic-ray boundary spectra. This involves solving a mixed Dirichlet-Von Neumann boundary value problem at the edge of the jet. The energetic particle distribution function f 0(r, p) at cylindrical radius r from the jet axis (assumed to lie along the z-axis) is given by convolving the particle momentum spectrum ${f}_{0}(\infty ,p^{\prime} )$ with the Green's function $G(r,p;p^{\prime} )$ , which describes the monoenergetic spectrum solution in which ${f}_{0}\to \delta (p-p^{\prime} )$ as r → ∞ . Previous work by Webb et al. studied only the Green's function solution for $G(r,p;p^{\prime} )$ . In this paper, we explore for the first time, solutions for more general and realistic forms for ${f}_{0}(\infty ,p^{\prime} )$ . The flow velocity u = u(r) e z is along the axis of the jet (the z-axis). u is independent of z, and u(r) is a monotonic decreasing function of r. The scattering time $\tau {(r,p)={\tau }_{0}(p/{p}_{0})}^{\alpha }$ in the shear flow region 0 < r < r 2, and $\tau {(r,p)={\tau }_{0}(p/{p}_{0})}^{\alpha }{(r/{r}_{2})}^{s}$ , where s > 0 in the region r > r 2 is outside the jet. Other original aspects of the analysis are (i) the use of cosmic ray flow lines in (r, p) space to clarify the particle spatial transport and momentum changes and (ii) the determination of the probability distribution ${\psi }_{p}(r,p;p^{\prime} )$ that particles observed at (r, p) originated from r → ∞ with momentum $p^{\prime} $ . The acceleration of ultrahigh-energy cosmic rays in active galactic nuclei jet sources is discussed. Leaky box models for electron acceleration are described.

Keywords: radio jets; high-energy cosmic radiation; ultra-high-energy cosmic radiation; relativistic jets
Characterizing Interplanetary Coronal Mass Ejection-related Forbush Decreases at Mercury Using MESSENGER Observations: Identification of a One- or Two-step Structure

The large-scale magnetic structure of interplanetary coronal mass ejections (ICMEs) has been shown to cause decreases in the galactic cosmic ray (GCR) flux measured in situ by spacecraft, known as Forbush decreases (Fds). We use measurements of the GCR count rate obtained by NASA's MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft during its orbital phase around Mercury to identify such Fds related to the passage of ICMEs and characterize their structure. Of the 42 ICMEs with corresponding high-quality GCR data, 79% are associated with a Fd. Thus, a total of 33 ICME-related Fds were identified, 24 of which (73%) have a two-step structure. We use a superposed epoch analysis to build an average Fd profile at MESSENGER and find that despite the variability of individual events, a two-step structure is produced and is directly linked with the magnetic boundaries of the ICME. By using results from previous studies at Earth and Mars, we also address whether two-step Fds are more commonly observed closer to the Sun; we found that, although likely, this is not conclusive when comparing to the wide range of results of previous studies conducted at Earth. Finally, we find that the percentage decrease in GCR flux of the Fd is greater at MESSENGER on average than at Earth and Mars, decreasing with increasing heliocentric distance. The relationship between the percentage decrease and maximum hourly decrease is also in agreement with previous studies, and follows trends relating to the expansion of ICMEs as they propagate through the heliosphere.

Keywords: solar coronal mass ejections; forbush effect; galactic cosmic rays; heliosphere