adsabs/SciX_UAT_keywords huggingface dataset:
Brightest Cluster Galaxies and Intracluster Light: Their Mass Distribution in the Innermost Regions of Groups and Clusters

We improve the model presented in Contini & Gu that describes the radial mass distribution of brightest cluster galaxies (BCGs) and the diffuse component also known as intracluster light (ICL), by assuming that the global BCG+ICL radial mass distribution follows the sum of three profiles: Jaffe and exponential profiles for the bulge and disk of the BCG, respectively, and a modified version of an NFW profile for the ICL. We take advantage of a wide sample of BCG+ICL systems simulated with our state-of-the-art semianalytic model to (a) investigate the reliability of our BCG+ICL distribution by looking at several scaling relations between the BCG+ICL stellar mass within different apertures and the total BCG+ICL/halo mass, at different redshifts; (b) make a prediction of the distance where the radial distribution transitions from BCG to ICL dominated. We find that our model nicely reproduces all the observed scaling relations investigated at the present time with a compelling degree of precision, but slightly biased low with respect to observations at higher redshifts (z ≳ 0.5). The transition radius predicted by our model is in good agreement with recent observational results, and spans a range between ~15 kpc and ~100 kpc. It mostly depends on the morphology of the BCG, whether it is bulge or disk dominated, on the amount of ICL with respect to the bulge and/or disk, and on the dynamical state of the group/cluster.

Keywords: galaxy clusters; galaxy evolution
Coma Anisotropy and the Rotation Pole of Interstellar Comet 2I/Borisov

Hubble Space Telescope observations of interstellar comet 2I/Borisov near perihelion show the ejection of large ( $\gtrsim 100$ μm) particles at $\lesssim 9$ m s-1 speeds, with estimated mass-loss rates of ∼35 kg s-1. The total mass loss from comet Borisov corresponds to loss of a surface shell on the nucleus only ∼0.4 m thick. This shell is thin enough to be susceptible to past chemical processing in the interstellar medium by cosmic rays, meaning that the ejected materials cannot necessarily be considered as pristine. Our high-resolution images reveal persistent asymmetry in the dust coma, best explained by a thermal lag on the rotating nucleus causing peak mass loss to occur in the comet nucleus afternoon. In this interpretation, the nucleus rotates with an obliquity of $30^\circ $ (pole direction R.A. = $205^\circ $ and decl. = $52^\circ $ ). The subsolar latitude varied from $-35^\circ $ (southern solstice) at the time of discovery to $0^\circ $ (equinox) in 2020 January, suggesting the importance of seasonal effects. Subsequent activity likely results from regions freshly activated as the northern hemisphere is illuminated for the first time.

Keywords: comets; long period comets
SOFIA FEEDBACK Survey: PDR Diagnostics of Stellar Feedback in Different Regions of RCW 49

We quantified the effects of stellar feedback in RCW 49 by determining the physical conditions in different regions using the [C II] 158 μm and [O I] 63 μm observations from SOFIA, the 12CO (3-2) observations from APEX, and the H2 line observations from Spitzer telescopes. Large maps of RCW 49 were observed with the SOFIA and APEX telescopes, while the Spitzer observations were only available toward three small areas. From our qualitative analysis, we found that the H2 0-0 S(2) emission line probes denser gas compared to the H2 0-0 S(1) line. In four regions ("northern cloud," "pillar," "ridge," and "shell"), we compared our observations with the updated PDR Toolbox models and derived the integrated far-ultraviolet flux between 6 and 13.6 eV (G 0), H nucleus density (n), temperatures, and pressures. We found the ridge to have the highest G 0 (2.4 × 103 Habing units), while the northern cloud has the lowest G 0 (5 × 102 Habing units). This is a direct consequence of the location of these regions with respect to the Wd2 cluster. The ridge also has a high density (6.4 × 103 cm-3), which is consistent with its ongoing star formation. Among the Spitzer positions, we found the one closest to the Wd2 cluster to be the densest, suggesting an early phase of star formation. Furthermore, the Spitzer position that overlaps with the shell was found to have the highest G 0, and we expect this to be a result of its proximity to an O9V star.

Keywords: photodissociation regions; stellar feedback; molecular clouds
Calcium Chemistry in Carbon-rich Circumstellar Environments: The Laboratory and Astronomical Discovery of Calcium Dicarbide, CaC2

Calcium dicarbide, CaC2, has been characterized at high resolution in the laboratory, and its main isotopologue, 40CaC2, has been assigned to 14 rotational emission lines between 14 and 115 GHz, including 12 previously unassigned lines, in the expanding molecular envelope of the evolved carbon star IRC+10216. Aided by high-level quantum calculations and measurements of multiple isotopologues, CaC2 is determined to be a T-shaped molecule with a highly ionic bond linking the metal atom to the C2 unit, very similar in structure to isovalent magnesium dicarbide (MgC2). The excitation of CaC2 is characterized by a very low rotational temperature of 5.8 ± 0.6 K and a kinetic temperature of 36 ± 16 K, similar to values derived for MgC2. On the assumption that the emission originates from a 30″ shell in IRC+10216, the column density of CaC2 is (5.6 ± 1.7) × 1011 cm‑2. CaC2 is only the second Ca-bearing molecule besides CaNC and only the second metal dicarbide besides MgC2 identified in space. Owing to the similarity between the predicted ion–molecule chemistry of Ca and Mg, a comparison of the CaC2 abundance with that of MgC2 and related species permits empirical inferences about the radiative association–dissociative recombination processes postulated to yield metal-bearing molecules in IRC+10216 and similar objects. * This work is based on observations done using the 100 m Green Bank Telescope (GBT), the Yebes 40 m telescope (projects 19A010, 20A017, 20B014, and 21A019), and the IRAM 30 m telescope. The 100 m GBT is an instrument of the Green Bank Observatory, which is a major research facility funded by the National Science Foundation and operated by Associated Universities, Inc. The Yebes 40 m radio telescope at Yebes Observatory is operated by the Spanish National Geographic Institute (Instituto Geográfico Nacional, IGN). IRAM is supported by INSU/CNRS (France), Max-Planck-Gesellschaft (MPG; Germany), and IGN (Spain).

Keywords: circumstellar envelopes; carbon stars; metal-containing molecules; laboratory astrophysics
The Orbit of NGC 5907 ULX-1

We report on the orbit of the binary system powering the most extreme ultraluminous X-ray pulsar known to date: NGC 5907 ULX-1 (hereafter ULX1). ULX1 has been the target of a substantial multi-instrument campaign, mainly in the X-ray band, but no clear counterparts are known in other bands. Although ULX1 is highly variable and pulsations can be transient (regardless of the source flux), the timing data collected so far allow us to investigate the orbit of this system. We find an orbital period ${P}_{\mathrm{orb}}={5.7}_{-0.6}^{+0.1}\,\mathrm{days}$ and a projected semi-axis ${A}_{1}={3.1}_{-0.9}^{+0.8}\,\mathrm{lt}\mbox{--}{\rm{s}}$ . The most likely ephemeris is P orb = 5.6585(6) days, A 1 = 3.1(4) lt-s, and the epoch of ascending nodes passage is T asc = 57751.37(5) MJD. However, there are six similar solutions acceptable within 3σ. We find further indications that ULX1 is a high-mass X-ray binary. This implies that we are observing its orbit face on, with an inclination <5°.

Keywords: ultraluminous x-ray sources; orbit determination; high mass x-ray binary stars; high time resolution astrophysics
PHANGS-JWST First Results: A Global and Moderately Resolved View of Mid-infrared and CO Line Emission from Galaxies at the Start of the JWST Era

We explore the relationship between mid-infrared (mid-IR) and CO rotational line emission from massive star-forming galaxies, which is one of the tightest scalings in the local universe. We assemble a large set of unresolved and moderately (~1 kpc) spatially resolved measurements of CO (1-0) and CO (2-1) intensity, I CO, and mid-IR intensity, I MIR, at 8, 12, 22, and 24 μm. The I CO versus I MIR relationship is reasonably described by a power law with slopes 0.7-1.2 and normalization I CO ~ 1 K km s-1 at I MIR ~ 1 MJy sr-1. Both the slopes and intercepts vary systematically with choice of line and band. The comparison between the relations measured for CO (1-0) and CO (2-1) allow us to infer that ${R}_{21}\propto {I}_{\mathrm{MIR}}^{0.2}$ , in good agreement with other work. The 8 μm and 12 μm bands, with strong polycyclic aromatic hydrocarbon (PAH) features, show steeper CO versus mid-IR slopes than the 22 and 24 μm, consistent with PAH emission arising not just from CO-bright gas but also from atomic or CO-dark gas. The CO-to-mid-IR ratio correlates with global galaxy stellar mass (M ⋆) and anticorrelates with star formation rate/M ⋆. At ~1 kpc resolution, the first four PHANGS-JWST targets show CO-to-mid-IR relationships that are quantitatively similar to our larger literature sample, including showing the steep CO-to-mid-IR slopes for the JWST PAH-tracing bands, although we caution that these initial data have a small sample size and span a limited range of intensities.

Keywords: disk galaxies; galaxy physics; molecular gas; dust continuum emission; infrared astronomy; millimeter astronomy
EDEN: Sensitivity Analysis and Transiting Planet Detection Limits for Nearby Late Red Dwarfs

Small planets are common around late-M dwarfs and can be detected through highly precise photometry by the transit method. Planets orbiting nearby stars are particularly important as they are often the best-suited for future follow-up studies. We present observations of three nearby M dwarfs referred to as EIC-1, EIC-2, and EIC-3, and use them to search for transits and set limits on the presence of planets. On most nights our observations are sensitive to Earth-sized transiting planets, and photometric precision is similar to or better than TESS for faint late-M dwarfs of the same magnitude (I ≈ 15 mag). We present our photometry and transit search pipeline, which utilizes simple median detrending in combination with transit least-squares-based transit detection. For these targets, and transiting planets between one and two Earth radii, we achieve an average transit detection probability of ∼60% between periods of 0.5 and 2 days, ∼30% between 2 and 5 days, and ∼10% between 5 and 10 days. These sensitivities are conservative compared to visual searches.

Keywords: exoplanet astronomy; exoplanets; habitable planets; transit photometry
GW170817 and GW190814: Tension on the Maximum Mass

The detection of the binary events GW170817 and GW190814 has provided invaluable constraints on the maximum mass of nonrotating configurations of neutron stars, MTOV. However, the large differences in the neutron-star masses measured in GW170817 and GW190814 has also lead to significant tension between the predictions for such maximum masses, with GW170817 suggesting that MTOV ≲ 2.3 M⊙, and GW190814 requiring MTOV ≳ 2.5 M⊙ if the secondary was a (non- or slowly rotating) neutron star at merger. Using a genetic algorithm, we sample the multidimensional space of parameters spanned by gravitational-wave and astronomical observations associated with GW170817. Consistent with previous estimates, we find that all of the physical quantities are in agreement with the observations if the maximum mass is in the range of ${M}_{\mathrm{TOV}}={2.210}_{-0.123}^{+0.116}\,{M}_{\odot }$ within a 2σ confidence level. By contrast, maximum masses with MTOV ≳ 2.5 M⊙, not only require efficiencies in the gravitational-wave emission that are well above the numerical-relativity estimates, but they also lead to a significant underproduction of the ejected mass. Hence, the tension can be released by assuming that the secondary in GW190814 was a black hole at merger, although it could have been a rotating neutron star before.

Keywords: neutron stars; nuclear astrophysics; gravitational waves; analytical mathematics
A Massive Protocluster Anchored by a Luminous Quasar at z = 6.63

Protoclusters, the progenitors of galaxy clusters, trace large scale structures in the early Universe and are important to our understanding of structure formation and galaxy evolution. To date, only a handful of protoclusters have been identified in the Epoch of Reionization. As one of the rarest populations in the early Universe, distant quasars that host active supermassive black holes are thought to reside in the most massive dark matter halos at that cosmic epoch and could thus potentially pinpoint some of the earliest protoclusters. In this Letter, we report the discovery of a massive protocluster around a luminous quasar at z = 6.63. This protocluster is anchored by the quasar and includes three [C II] emitters at z ∼ 6.63, 12 spectroscopically confirmed Lyα emitters (LAEs) at 6.54 < z ≤ 6.64, and a large number of narrow-band-imaging selected LAE candidates at the same redshift. This structure has an overall overdensity of $\delta ={3.3}_{-0.9}^{+1.1}$ within ∼35 × 74 cMpc2 on the sky and an extreme overdensity of δ > 30 in its central region (i.e., R ≲ 2 cMpc). We estimate that this protocluster will collapse into a galaxy cluster with a mass of ${6.9}_{-1.4}^{+1.2}\times {10}^{15}\,{M}_{\odot }$ at the current epoch, more massive than the most massive clusters known in the local Universe such as Coma. In the quasar vicinity, we discover a double-peaked LAE, which implies that the quasar has a UV lifetime greater than 0.8 Myrs and has already ionized its surrounding intergalactic medium.

Keywords: quasars; protoclusters; supermassive black holes; reionization; early universe
On the Spectral Evolution of Hot White Dwarf Stars. III. The PG 1159-DO-DB-DQ Evolutionary Channel Revisited

We continue our comprehensive theoretical investigation of the spectral evolution of white dwarfs based on sophisticated simulations of element transport. In this paper, we focus on the transformation of PG 1159 stars into DO/DB white dwarfs due to the gravitational settling of heavy elements and then into DQ white dwarfs through the convective dredge-up of carbon. We study the impact of several physical parameters on the evolution of the surface carbon abundance over a wide range of effective temperatures. In the hot PG 1159 and DO phases, our calculations confirm that the temperature of the PG 1159-to-DO transition depends sensitively on the stellar mass and the wind mass-loss rate. We show that measured carbon abundances of DOZ white dwarfs are mostly accounted for by our models, with the notable exception of the coolest DOZ stars. In the cooler DB and DQ phases, the predicted atmospheric composition is strongly influenced by the stellar mass, the thickness of the envelope, the initial carbon content, the efficiency of convective overshoot, and the presence of residual hydrogen. We demonstrate that, under reasonable assumptions, our simulations reproduce very well the observed carbon abundance pattern of DQ stars, which thus allows us to constrain the extent of the overshoot region in cool helium-rich white dwarfs. We also argue that our calculations naturally explain a number of recent empirical results, such as the relative excess of low-mass DQ stars and the presence of trace hydrogen and/or carbon at the surface of most DC and DZ stars.

Keywords: white dwarf stars; stellar evolutionary models; do stars; db stars; dq stars; atmospheric composition; stellar diffusion; stellar winds; stellar convection envelopes
First Infrared Coronal Spectra from DKIST/Cryo-NIRSP: Comparisons with Global MHD Models

The Cryogenic Near-Infrared Spectropolarimeter (Cryo-NIRSP) is now conducting science operations at the National Science Foundation's Daniel K. Inouye Solar Telescope (DKIST). We report results obtained during instrument commissioning that advance multiwavelength coronagraphic observations in the infrared. This includes the first observations of the Fe XIII 1075 nm, Fe XIII 1079 nm, Si X 1430 nm, and Si IX 3934 nm forbidden lines. The Si IX observations, in particular, significantly improve upon the few previous ground-based detections and open up this diagnostic for more routine study. We analyse long-slit spectra in each line sampling elongations from 1.06 to 1.52 solar radii above the northeast solar limb on 2022 February 14. Line characteristics as a function of radial distance are derived and discussed in comparison to modeled emission emergent from global coronal magnetohydrodynamic models with different heating prescriptions. We find favorable correspondence between the observations and different aspects of these models, and further demonstrate the utility of infrared observations for constraining coronal models. Continued DKIST/Cryo-NIRSP observations including polarimetric data, together with ongoing improvements in data calibrations, promise significant value for coronal studies.

Keywords: solar corona; solar coronal lines; solar e corona; solar coronal streamers
Elemental Abundances in the Diffuse Interstellar Medium from Joint Far-ultraviolet and X-Ray Spectroscopy: Iron, Oxygen, Carbon, and Sulfur

In this study, we investigate interstellar absorption lines along the line of sight toward the galactic low-mass X-ray binary Cygnus X-2. We combine absorption line data obtained from high-resolution X-ray spectra collected with the Chandra and XMM-Newton satellites, along with far-UV absorption lines observed by the Hubble Space Telescope's (HST) Cosmic Origins Spectrograph (COS) instrument. Our primary objective is to understand the abundance and depletion of oxygen, iron, sulfur, and carbon. To achieve this, we have developed an analysis pipeline that simultaneously fits both the UV and X-ray data sets. This novel approach takes into account the line-spread function of HST/COS, enhancing the precision of our results. We examine the absorption lines of Fe II, S II, C II, and C I present in the far-UV spectrum of Cygnus X-2, revealing the presence of at least two distinct absorbers characterized by different velocities. Additionally, we employ Cloudy simulations to compare our findings concerning the ionic ratios for the studied elements. We find that gaseous iron and sulfur exist in their singly ionized forms, Fe II and S II, respectively, while the abundances of C II and C I do not agree with the Cloudy simulations of the neutral ISM. Finally, we explore discrepancies in the X-ray atomic data of iron and discuss their impact on the overall abundance and depletion of iron.

Keywords: chemical abundances
Formation of Solar Quiescent Coronal Loops through Magnetic Reconnection in an Emerging Active Region

Coronal loops are the building blocks of solar active regions. However, their formation mechanism remains poorly understood. Here we present direct observational evidence for the formation of coronal loops through magnetic reconnection as new magnetic fluxes emerge into the solar atmosphere. Extreme-ultraviolet observations by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO) clearly show the newly formed loops following magnetic reconnection within a plasma sheet. Formation of the loops is also seen in the Hα line-core images taken by the New Vacuum Solar Telescope. Observations from the Helioseismic and Magnetic Imager on board SDO show that a positive-polarity flux concentration moves toward a negative-polarity one with a speed of ~0.4 km s-1 before the formation of coronal loops. During the loop formation process, we found signatures of flux cancellation and subsequent enhancement of the transverse field between the two polarities. The three-dimensional magnetic field structure reconstructed through a magnetohydrostatic model shows field lines consistent with the loops in AIA images. Numerous bright blobs with an average width of 1.37 Mm appear intermittently in the plasma sheet and move upward with a projected velocity of ~114 km s-1. The temperature, emission measure, and density of these blobs are about 3 MK, 2.0 × 1028 cm-5, and 1.2 × 1010 cm-3, respectively. A power spectral analysis of these blobs indicates that the observed reconnection is likely not dominated by a turbulent process. We have also identified flows with a velocity of 20-50 km s-1 toward the footpoints of the newly formed coronal loops.

Keywords: solar coronal loops; solar magnetic reconnection; solar physics; solar active regions; solar magnetic flux emergence
A Survey for C II Emission-line Stars in the Large Magellanic Cloud

We present a narrowband imaging survey of the Large Magellanic Cloud (LMC), designed to isolate the C II λλ7231, 7236 emission lines in objects as faint as mλ7400 ∼ 18. The work is motivated by the recent serendipitous discovery in the LMC of the first confirmed extragalactic [WC11] star, whose spectrum is dominated by C II emission, and the realization that the number of such objects is currently largely unconstrained. The survey, which imaged ∼50 deg2 using on-band and off-band filters, will significantly increase the total census of these rare stars. In addition, each new LMC [WC] star has a known luminosity, a quantity quite uncertain in the Galactic sample. Multiple known C II emitters were easily recovered, validating the survey design. We find 38 new C II emission candidates; spectroscopy of the complete sample will be needed to ascertain their nature. In a preliminary spectroscopic reconnaissance, we observed three candidates, finding C II emission in each. One is a new [WC11]. Another shows both the narrow C II emission lines characteristic of a [WC11], but also broad emission of C IV, O V, and He II characteristic of a much hotter [WC4] star; we speculate that this is a binary [WC]. The third object shows weak C II emission, but the spectrum is dominated by a dense thicket of strong absorption lines, including numerous O II transitions. We conclude it is likely an unusual hot, hydrogen-poor post-AGB star, possibly in transition from [WC] to white dwarf. Even lacking a complete spectroscopic program, we can infer that late [WC] stars do not dominate the central stars of LMC planetary nebulae, and that the detected C II emitters are largely of an old population.

Keywords: wc stars; planetary nebulae nuclei
Detailed Shapes of the Line-of-sight Velocity Distributions in Massive Early-type Galaxies from Nonparametric Spectral Models

We present the first systematic study of the detailed shapes of the line-of-sight velocity distributions (LOSVDs) in nine massive early-type galaxies (ETGs) using the novel nonparametric modeling code WINGFIT. High-signal spectral observations with the Multi-Unit Spectroscopic Explorer (MUSE) at the Very Large Telescope allow us to measure between 40 and 400 individual LOSVDs in each galaxy at a signal-to-noise ratio level better than 100 per spectral bin and to trace the LOSVDs all the way out to the highest stellar velocities. We extensively discuss potential LOSVD distortions due to template mismatch and strategies to avoid them. Our analysis uncovers a plethora of complex, large-scale kinematic structures for the shapes of the LOSVDs. Most notably, in the centers of all ETGs in our sample, we detect faint, broad LOSVD "wings" extending the line-of-sight velocities, v los, well beyond 3σ to v los ~ ± 1000-1500 km s-1 on both sides of the peak of the LOSVDs. These wings likely originate from point-spread function effects and contain velocity information about the very central unresolved regions of the galaxies. In several galaxies, we detect wings of similar shape also toward the outer parts of the MUSE field of view. We propose that these wings originate from faint halos of loosely bound stars around the ETGs, similar to the cluster-bound stellar envelopes found around many brightest cluster galaxies.

Keywords: elliptical galaxies; stellar kinematics; galaxy dark matter halos; supermassive black holes; galaxy spectroscopy; galaxy structure