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DOE OSTI2026

H I Depletion Begins Well Beyond the Virial Radius: A FAST Stacking Study of 36 Galaxy Clusters to 5 × R 200

Abstract We present a stacking study of the neutral atomic hydrogen (H i ) content in and around 36 local galaxy clusters at z < 0.07, using a combination of the FAST All Sky H i survey (FASHI) and the extensive spectroscopic catalog mainly from the Dark Energy Spectroscopic Instrument (DESI). We employ spectral stacking techniques to probe the average H i mass and HI-to-stellar mass ratio ( M HI / M * ) for member galaxies down to stellar masses of M * ∼ 10 9 M ⊙ , spanning a projected cluster-centric distance of up to 5 R 200 . Our analysis reveals a pronounced environmental effect; both M HI and M HI / M * decrease steadily toward the cluster center, dropping by ∼0.5 dex on average from the outskirts to the core. Crucially, we find that M HI / M * of galaxies remain lower than the field galaxies even at the 5 R 200 . This provides direct, statistical evidence for substantial gas stripping and preprocessing in the cluster outskirts, likely occurring in infalling groups and large-scale filaments. By further splitting the sample by g − r color, we show that the H i deficiency persists at fixed galaxy color; even the bluest cluster members exhibit ∼0.5 dex lower M HI / M * than field galaxies of similar color, reflecting environmental effects on the cold gas reservoir prior to full optical transformation. The total H i mass within clusters and their outskirts agrees broadly with predictions from cosmological simulations. Our results underscore the critical role of the extended cluster environment in quenching galaxies by depleting their cold gas reservoirs well before they enter the dense cluster core.

Cheng, Cheng [Chinese Academy of Sciences South Am↗

DOE OSTI2025

Evaluating the Potential to Constrain Dark Matter Annihilation with Fermi-LAT Observations of Ultrafaint Compact Stellar Systems

Recent results from numerical simulations and models of galaxy formation suggest that recently discovered ultrafaint compact stellar systems (UFCSs) in the halo of the Milky Way (MW) may be some of the smallest and faintest galaxies. If this is the case, these systems would be attractive targets for indirect searches of weakly interacting massive particle dark matter (DM) annihilation due to their relative proximity and high expected DM content. In this study, we analyze 14.3 yr of γ-ray data collected by the Fermi-Large Area Telescope coincident with 26 UFCSs. No significant excess γ-ray emission is detected, and we present γ-ray flux upper limits for these systems. Assuming that the UFCSs are DM-dominated galaxies consistent with being among the faintest and least massive MW dwarf spheroidal (dSph) satellite galaxies, we derive the projected sensitivity for a DM annihilation signal. We find that observations of UFCSs have the potential to yield some of the most powerful constraints on DM annihilation, with sensitivity comparable to observations of known dSphs and the Galactic center. This result emphasizes the importance of precise kinematic studies of UFCSs to empirically determine their DM content.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2021

Terminus: A Versatile Simulator for Space-based Telescopes

Space-based telescopes offer unparalleled opportunities for characterizing exoplanets, solar system bodies, and stellar objects. However, observatories in low-Earth orbits (e.g., Hubble, CHaracterising ExOPlanets Satellite, Twinkle, and an ever-increasing number of cubesats) cannot always be continuously pointed at a target due to Earth obscuration. For exoplanet observations consisting of transit, or eclipse, spectroscopy, this causes gaps in the light curve, which reduces the information content and can diminish the science return of the observation. Terminus, a time-domain simulator, has been developed to model the occurrence of these gaps to predict the potential impact on future observations. The simulator is capable of radiometrically modeling exoplanet observations as well as producing light curves and spectra. Here, Terminus is baselined on the Twinkle mission, but the model can be adapted for any space-based telescope and is especially applicable to those in a low-Earth orbit. Terminus also has the capability to model observations of other targets such as asteroids or brown dwarfs.

47 OTHER INSTRUMENTATION↗

DOE OSTI2023

Barless flocculent galaxies: a dynamic puzzle

We draw attention to the bright galaxies that do not show a bar in their structure but have a flocculent spiral structure. Using the THINGS and HERACLES kinematic data for four barless galaxies (NGC 2841, NGC 3512, NGC 5055, NGC 7331), we built their mass models including dark haloes. We concluded that the fraction of the dark matter does not exceed 50 per cent within the optical radii of the galaxies. This is too little to explain the lack of a bar in these galaxies. In an attempt to understand the featureless structure of these galaxies, we constructed several N-body models with an initially reduced content of dark matter. We concluded that, in addition to the low mass of the dark halo, the decisive factor that leads to a barless disc is the start from an initially unstable state. An isolated dynamically cold disc (with the Toomre parameter Q < 0.5) settled into rotational equilibrium passes through the short stage of violent instability with fragmentation and formation of stellar clumps. After that, it evolves passively and ends up with a featureless structure. We assume that the barless flocculent galaxies studied in this work may be descendants of galaxies at high redshifts with rotation curves that are consistent with the high mass fraction of baryons relative to the total dark matter halo.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2021

The Red Supergiant Content of M31 and M33

We identify red supergiants (RSGs) in our spiral neighbors M31 and M33 using near-IR (NIR) photometry complete to a luminosity limit of logL/L{sub ⊙}=4.0. Our archival survey data cover 5 deg{sup 2} of M31, and 3 deg{sup 2} for M33, and are likely spatially complete for these massive stars. Gaia is used to remove foreground stars, after which the RSGs can be separated from asymptotic giant branch (AGB) stars in the color–magnitude diagram. The photometry is used to derive effective temperatures and bolometric luminosities via MARCS stellar atmosphere models. The resulting H-R diagrams show superb agreement with the evolutionary tracks of the Geneva evolutionary group. Our census includes 6400 RSGs in M31 and 2850 RSGs in M33 within their Holmberg radii; by contrast, only a few hundred RSGs are known so far in the Milky Way. Our catalog serves as the basis for a study of the RSG binary frequency being published separately, as well as future studies relating to the evolution of massive stars. Here we use the matches between the NIR-selected RSGs and their optical counterparts to show that the apparent similarity in the reddening of OB stars in M31 and M33 is the result of Malmquist bias; the average extinction in M31 is likely higher than that of M33. As expected, the distribution of RSGs follows that of the spiral arms, while the much older AGB population is more uniformly spread across each galaxy’s disk.

47 OTHER INSTRUMENTATION↗

DOE OSTI2023

Catching Tidal Dwarf Galaxies at a Later Evolutionary Stage with ALFALFA

We present deep optical imaging and photometry of four objects classified as “Almost-Dark” galaxies in the Arecibo Legacy Fast Arecibo L-band Feed Array (ALFALFA) survey because of their gas-rich nature and extremely faint or missing optical emission in existing catalogs. They have H I masses of 10 7 –10 9 M ⊙ and distances of ~9–100 Mpc. Observations with the WIYN 3.5 m telescope and One Degree Imager reveal faint stellar components with central surface brightnesses of ~24–25 m - ag arcsec 2 in the g band. We also present the results of H I synthesis observations with the Westerbork Synthesis Radio Telescope. These Almost-Dark galaxies have been identified as possible tidal dwarf galaxies (TDGs) based on their proximity to one or more massive galaxies. We demonstrate that AGC 229398 and AGC 333576 likely have the low dark matter content and large effective radii representative of TDGs. They are located much farther from their progenitors than previously studied TDGs, suggesting they are older and more evolved. AGC 219369 is likely dark matter dominated, while AGC 123216 has a dark matter content that is unusually high for a TDG, but low for a normal dwarf galaxy. We consider possible mechanisms for the formation of the TDG candidates such as a traditional major merger scenario and gas ejection from a high-velocity flyby. Blind H I surveys like ALFALFA enable the detection of gas-rich, optically faint TDGs that can be overlooked in other surveys, thereby providing a more complete census of the low-mass galaxy population and an opportunity to study TDGs at a more advanced stage of their life cycle.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2022

Investigating the architecture and internal structure of the TOI-561 system planets with CHEOPS, HARPS-N, and TESS

ABSTRACT We present a precise characterization of the TOI-561 planetary system obtained by combining previously published data with TESS and CHEOPS photometry, and a new set of 62 HARPS-N radial velocities (RVs). Our joint analysis confirms the presence of four transiting planets, namely TOI-561 b (P = 0.45 d, R = 1.42 R⊕, M = 2.0 M⊕), c (P = 10.78 d, R = 2.91 R⊕, M = 5.4 M⊕), d (P = 25.7 d, R = 2.82 R⊕, M = 13.2 M⊕), and e (P = 77 d, R = 2.55 R⊕, M = 12.6 R⊕). Moreover, we identify an additional, long-period signal (>450 d) in the RVs, which could be due to either an external planetary companion or to stellar magnetic activity. The precise masses and radii obtained for the four planets allowed us to conduct interior structure and atmospheric escape modelling. TOI-561 b is confirmed to be the lowest density (ρb = 3.8 ± 0.5 g cm−3) ultra-short period (USP) planet known to date, and the low metallicity of the host star makes it consistent with the general bulk density-stellar metallicity trend. According to our interior structure modelling, planet b has basically no gas envelope, and it could host a certain amount of water. In contrast, TOI-561 c, d, and e likely retained an H/He envelope, in addition to a possibly large water layer. The inferred planetary compositions suggest different atmospheric evolutionary paths, with planets b and c having experienced significant gas loss, and planets d and e showing an atmospheric content consistent with the original one. The uniqueness of the USP planet, the presence of the long-period planet TOI-561 e, and the complex architecture make this system an appealing target for follow-up studies.

Lacedelli, G. (ORCID:0000000241977374)↗

DOE OSTI2023

The bar rotation rate as a diagnostic of dark matter content in the centre of disc galaxies

We investigate the link between the bar rotation rate and dark matter content in barred galaxies by concentrating on the cases of the lenticular galaxies NGC 4264 and NGC 4277. These two gas-poor galaxies have similar morphologies, sizes, and luminosities. But, NGC 4264 hosts a fast bar, which extends to nearly the corotation, while the bar embedded in NGC 4277 is slow and falls short of corotation. We derive the fraction of dark matter ƒ DM, bar within the bar region from Jeans axisymmetric dynamical models by matching the stellar kinematics obtained with the MUSE integral-field spectrograph and using SDSS images to recover the stellar mass distribution. We build mass-follows-light models as well as mass models with a spherical halo of dark matter, which is not tied to the stars. We find that the inner regions of NGC 4277 host a larger fraction of dark matter (⁠ƒ DM,bar = 0.53±0.02⁠) with respect to NGC 4264 (⁠(⁠ƒ DM,bar = 0.33±0.04⁠) in agreement with the predictions of theoretical works and the findings of numerical simulations, which have found that fast bars live in baryon-dominated discs, whereas slow bars experienced a strong drag from the dynamical friction due to a dense DM halo. This is the first time that the bar rotation rate is coupled to fDM, bar derived from dynamical modelling.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2023

The Baryonic Content of Galaxies Mapped by MaNGA and the Gas Around Them

We analyze the cool gas in and around 14 nearby galaxies (at z < 0.1) mapped with the Sloan Digital Sky Survey IV MaNGA survey by measuring absorption lines produced by gas in spectra of background quasars/active galactic nuclei at impact parameters of 0–25 effective radii from the galactic centers. Using Hubble Space Telescope/Cosmic Origins Spectrograph, we detect absorption at the galactic redshift and measure or constrain column densities of neutral (H I, N I, O I, and Ar I), low-ionization (Si II, S II, C II, N II, and Fe II), and high-ionization (Si III, Fe III, N v, and O vI) species for 11 galaxies. We derive the ionization parameter and ionization-corrected metallicity using cloudy photoionization models. The H i column density ranges from ~1013 to ~1020 cm-2 and decreases with impact parameter for r ≳ Re. Galaxies with higher stellar mass have weaker H I absorption. Comparing absorption velocities with MaNGA radial velocity maps of ionized gas line emissions in galactic disks, we find that the neutral gas seen in absorption corotates with the disk out to ~10 R e . Sight lines with lower elevation angles show lower metallicities, consistent with the metallicity gradient in the disk derived from MaNGA maps. Higher-elevation angle sight lines show higher ionization, lower H I column density, supersolar metallicity, and velocities consistent with the direction of galactic outflow. Our data offer the first detailed comparisons of circumgalactic medium (CGM) properties (kinematics and metallicity) with extrapolations of detailed galaxy maps from integral field spectroscopy; similar studies for larger samples are needed to more fully understand how galaxies interact with their CGM.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2026

H I Gas and Star Formation in Major Galaxy Pairs from the FAST All Sky H I Survey (FASHI)

Atomic hydrogen (H I ) plays a fundamental role in fueling star formation in galaxies. However, the behavior of H I gas in interacting systems, particularly galaxy pairs, remains elusive. In this work, we investigate the H I content of major mergers by crossmatching the extragalactic H I catalog from the Five-hundred-meter Aperture Spherical radio Telescope (FAST) All-Sky H I Survey with a previously established sample of isolated galaxy pairs. With the superior sensitivity of FAST, we have constructed the largest sample of major mergers with H I detections, consisting of 440 galaxy pairs: 364 spiral-spiral (S+S) and 76 spiral-elliptical (S+E) systems. We examine the H I gas fraction (f H I ), star formation rate (SFR), and H I star formation efficiency (SFE H I = SFR/M H I ) for individual galaxies in pairs. The control sample is matched in both stellar mass and redshift. We find that paired galaxies, particularly those in pairs with small projected separations (d p < 50 h −1 kpc), exhibit systematically lower (by 8.8%) H I gas fractions compared to the control galaxies. The SFR is enhanced for galaxies in the S+S pairs. The SFE H I is ∼15% higher for galaxies in the S+S pairs than in the control galaxies, while spiral galaxies in the S+E pairs show no significant difference in SFE H I compared to the control sample. These findings suggest that the merger process triggers efficient H I gas depletion and enhances star formation, especially in close S+S pairs. Notably, our sample includes 26 red spirals in paired systems. These galaxies exhibit H I deficiency and suppressed star formation activity compared to the isolated galaxies, indicating that interactions may affect quiescent spirals differently, potentially due to mechanisms similar to those of ellipticals.

Yan, Shulan 淑澜鄢 [Xiamen University (China); SDSS C↗

DOE OSTI2024

Copacabana: a probabilistic membership assignment method for galaxy clusters

Cosmological analyses using galaxy clusters in optical/near-infrared photometric surveys require robust characterization of their galaxy content. Precisely determining which galaxies belong to a cluster is crucial. In this paper, we present the COlor Probabilistic Assignment of Clusters And BAyesiaN Analysis (Copacabana) algorithm. Copacabana computes membership probabilities for all galaxies within an aperture centred on the cluster using photometric redshifts, colours, and projected radial probability density functions. We use simulations to validate Copacabana and we show that it achieves up to 89 per cent membership accuracy with a mild dependence on photometric redshift uncertainties and choice of aperture size. We find that the precision of the photometric redshifts has the largest impact on the determination of the membership probabilities followed by the choice of the cluster aperture size. We also quantify how much these uncertainties in the membership probabilities affect the stellar mass–cluster mass scaling relation, a relation that directly impacts cosmology. Using the sum of the stellar masses weighted by membership probabilities (⁠μ * ⁠) as the observable, we find that Copacabana can reach an accuracy of 0.06 dex in the measurement of the scaling relation at low redshift for a Legacy Survey of Space and Time type survey. These results indicate the potential of Copacabana and μ * to be used in cosmological analyses of optically selected clusters in the future.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2021

Galaxy assembly bias and large-scale distribution: a comparison between IllustrisTNG and a semi-analytic model

In this work, we compare large scale structure observables for stellar mass selected samples at z = 0, as predicted by two galaxy models, the hydrodynamical simulation IllustrisTNG and the Santa-Cruz semi-analytic model (SC-SAM). Although both models have been independently calibrated to match observations, rather than each other, we find good agreement between the two models for two-point clustering and galaxy assembly bias signatures. The models also show a qualitatively similar response of occupancy and clustering to secondary halo parameters other than mass, such as formation history and concentration, although with some quantitative differences. Thus, our results demonstrate that the galaxy–halo relationships in SC-SAM and TNG are quite similar to first order. However, we also find areas in which the models differ. For example, we note a strong correlation between halo gas content and environment in TNG, which is lacking in the SC-SAM, as well as differences in the occupancy predictions for low-mass haloes. Moreover, we show that higher order statistics, such as cumulants of the density field, help us to accurately describe the galaxy distribution and discriminate between models that show degenerate behaviour for two-point statistics. Our results suggest that SAMs are a promising cost-effective and intuitive method for generating mock catalogues for next generation cosmological surveys.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2025

Counterpart identification and classification for eRASS1 and characterisation of the active galactic nuclei content

Context. Accurately accounting for the Active Galactic Nucleus (AGN) phase in galaxy evolution requires a large, clean AGN sample. This is now possible with SRG/eROSITA, which completed its first all-sky X-ray survey (eRASS1) on June 12, 2020. The public Data Release 1 (DR1, Jan 31, 2024) includes 930,203 sources from the western Galactic hemisphere. Aims. The data enable the selection of a large AGN sample and the discovery of rare sources. However, scientific return depends on accurate characterisation of the X-ray emitters, requiring high-quality multi-wavelength data. This paper presents the identification and classification of optical and infrared counterparts to eRASS1 sources. Methods. Counterparts to eRASS1 X-ray point sources were identified using Gaia DR3, CatWISE2020, and Legacy Survey DR10 (LS10) with the Bayesian NWAY algorithm and trained priors. Sources were classified as Galactic or extragalactic via a machine-learning model combining optical/IR and X-ray properties, trained on a reference sample. For extragalactic LS10 sources, photometric redshifts were computed using CIRCLEZ. Results. Within the LS10 footprint, all 656,614 eROSITA/DR1 sources have at least one possible optical counterpart; ∼570 000 are extragalactic and likely AGN. Half are new detections compared to AllWISE, Gaia, and Quaia AGN catalogues. Gaia and CatWISE2020 counterparts are less reliable, due to the survey’s shallowness and the limited amount of features available to assess the probability of being an X-ray emitter. In the Galactic plane, where the overdensity of stellar sources also increases the chance of associations, using conservative reliability cuts, we identified approximately 18 000 Gaia and 55 000 CatWISE2020 extragalactic sources. Conclusions. We have released three high-quality counterpart catalogues – plus the training and validation sets – as a benchmark for the field. These datasets have many applications, but in particular, they empower researchers to build AGN samples tailored for completeness and purity, accelerating the hunt for the Universe’s most energetic engines.

X-rays: general↗

DOE OSTI2022

On the origin of red spirals: does assembly bias play a role?

The formation of the red spirals is a puzzling issue in the standard picture of galaxy formation and evolution. Most studies attribute the colour of the red spirals to different environmental effects. We analyze a volume limited sample from the SDSS to study the roles of small-scale and large-scale environments on the colour of spiral galaxies. We compare the star formation rate, stellar age and stellar mass distributions of the red and blue spirals and find statistically significant differences between them at 99.9% confidence level. The red spirals inhabit significantly denser regions than the blue spirals, explaining some of the observed differences in their physical properties. However, the differences persist in all types of environments, indicating that the local density alone is not sufficient to explain the origin of the red spirals. Using an information theoretic framework, we find a small but non-zero mutual information between the colour of spiral galaxies and their large-scale environment that are statistically significant (99.9% confidence level) throughout the entire length scale probed. Such correlations between the colour and the large-scale environment of spiral galaxies may result from the assembly bias. Thus both the local environment and the assembly bias may play essential roles in forming the red spirals. The spiral galaxies may have different assembly history across all types of environments. We propose a picture where the differences in the assembly history may produce spiral galaxies with different cold gas content. Such a difference would make some spirals more susceptible to quenching. Finally, in all environments, the spirals with high cold gas content could delay the quenching and maintain a blue colour, whereas the spirals with low cold gas fractions would be easily quenched and become red.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2023

Weak Gravitational Lensing of Low Surface Brightness Galaxies in the Dark Energy Year 3 Catalog

We present galaxy-galaxy lensing measurements of a sample of low surface brightness galaxies (LSBGs) drawn from the Dark Energy Survey Year 3 (Y3) data. LSBGs are diffuse galaxies with a surface brightness dimmer than the ambient night sky. Given their faintness, the use of standard observational techniques proves challenging. Weak gravitational lensing probes both the baryonic and dark matter content of galaxies, rendering it a powerful technique to estimate LSBG masses. The LSBG lens sample consists of 23, 790 total extended galaxies separated into red and blue color types at $g-i\ge 0.60$ and $g-i\le 0.60$, respectively. We use the Y3 \sc{metacalibration} shape catalog as the source sample, with a number density of $5.59 \mathrm{gal}/\mathrm{arcmin}^2$. We measure the tangential shear around the lens galaxies across angular scales of $0.25-400$ arcmin and find a signal-to-noise of 6.67 for red galaxies, 2.17 for blue galaxies, and 5.30 for the total sample. We fit a model built from two NFW profiles corresponding to the LSBG dark matter subhalo and host halo to the red LSBG shear measurements with an MCMC. We estimate the host halo mass at $7.3 ^{+2.0}_{-1.6}\times 10^{12} M_\mathrm{\odot}$. We place a 95\% upper bound on the subhalo mass at $3\times 10^{11} M_\mathrm{\odot}$. We utilize the lens sample photometry to obtain an estimate of the red LSBG stellar mass distribution. We compare the ratio between the stellar mass and the subhalo mass to the parameterized, satellite-specific SHMR. This work represents the first example of an attempted constraint on the masses of LSBGs using weak gravitational lensing.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2023

Weak Gravitational Lensing of Low Surface Brightness Galaxies in the DES Year 3 Catalog

We present galaxy-galaxy lensing measurements of a sample of low surface brightness galaxies (LSBGs) drawn from the Dark Energy Survey Year 3 (Y3) data. LSBGs are diffuse galaxies with a surface brightness dimmer than the ambient night sky. Given their faintness, the use of standard observational techniques proves challenging. Weak gravitational lensing probes both the baryonic and dark matter content of galaxies, rendering it a powerful technique to estimate LSBG masses. The LSBG lens sample consists of 23, 790 total extended galaxies separated into red and blue color types at $g-i\ge 0.60$ and $g-i\le 0.60$, respectively. We use the Y3 \metacal\ shape catalog as the source sample, with a number density of {\color{red}$5.59 \mathrm{gal}/\mathrm{arcmin}^2$}. We measure the tangential shear around the lens galaxies across angular scales of $0.25-400$ arcmin and find a signal-to-noise of 6.67 for red galaxies, 2.17 for blue galaxies, and 5.30 for the total sample. W e fit a model built from two NFW profiles corresponding to the LSBG dark matter subhalo and host halo to the red LSBG shear measurements with an MCMC. We estimate the host halo mass at $7.3 ^{+2.0}_{-1.6}\times 10^{12} M_\mathrm{\odot}$. We place a 95\% upper bound on the subhalo mass at $2.8\times 10^{11} M_\mathrm{\odot}$. We utilize the lens sample photometry to obtain an estimate of the red LSBG stellar mass distribution. We compare the ratio between the stellar mass and the subhalo mass to the parameterized, satellite-specific SHMR \citep{Moster2010}. This work represents the first example of an attempted constraint on the masses of LSBGs using weak gravitational lensing.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2023

The Dependence of Iron-rich Metal-poor Star Occurrence on Galactic Environment Supports an Origin in Thermonuclear Supernova Nucleosynthesis

It has been suggested that a class of chemically peculiar metal-poor stars called iron-rich metal-poor (IRMP) stars formed from molecular cores with metal contents dominated by thermonuclear supernova nucleosynthesis. If this interpretation is accurate, then IRMP stars should be more common in environments where thermonuclear supernovae were important contributors to chemical evolution. Conversely, IRMP stars should be less common in environments where thermonuclear supernovae were not important contributors to chemical evolution. At constant [Fe/H] ≲ -1, the Milky Way's satellite classical dwarf spheroidal (dSph) galaxies and the Magellanic Clouds have lower [α/Fe] than the Milky Way field and globular cluster populations. This difference is thought to demonstrate the importance of thermonuclear supernova nucleosynthesis for the chemical evolution of the Milky Way's satellite classical dSph galaxies and the Magellanic Clouds. We use data from the Sloan Digital Sky Survey Apache Point Observatory Galactic Evolution Experiment and Gaia to infer the occurrence of IRMP stars in the Milky Way's satellite classical dSph galaxies η dSph and the Magellanic Clouds η Mag , as well as in the Milky Way field η MWF and globular cluster populations η MWGC . In order of decreasing occurrence, we find η dSph = $0.07$$^{+0.02}_{-0.02}$, η Mag = $0.037$$^{+0.007}_{-0.006}$, η MWF = $0.0013$$^{+0.0006}_{-0.0005}$, and a 1σ upper limit η MWGC < 0.00057. These occurrences support the inference that IRMP stars formed in environments dominated by thermonuclear supernova nucleosynthesis and that the time lag between the formation of the first and second stellar generations in globular clusters was longer than the thermonuclear supernova delay time.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2022

Discovery of a Damped Lyα Absorber Originating in a Spectacular Interacting Dwarf Galaxy Pair at z = 0.026

We present the discovery of neutral gas detected in both damped Lyα absorption (DLA) and H I 21 cm emission outside of the stellar body of a galaxy, the first such detection in the literature. A joint analysis between the Cosmic Ultraviolet Baryon Survey and the MeerKAT Absorption Line Survey reveals an H I bridge connecting two interacting dwarf galaxies (log (M star /M ⊙ ) = 8.5 ± 0.2) that host a z = 0.026 DLA with log[N(H I )/cm –2 ] = 20.60 ± 0.05 toward the QSO J2339–5523 (z QSO = 1.35). At impact parameters of d = 6 and 33 kpc, the dwarf galaxies have no companions more luminous than ≈0.05L * within at least Δv = ±300 km s –1 and d ≈ 350 kpc. The H I 21 cm emission is spatially coincident with the DLA at the 2σ–3σ level per spectral channel over several adjacent beams. However, H I 21 cm absorption is not detected against the radio-bright QSO; if the background UV and radio sources are spatially aligned, the gas is either warm or clumpy (with a spin temperature to covering factor ratio T s /f c > 1880 K). Observations with VLT-MUSE demonstrate that the α-element abundance of the ionized interstellar medium (ISM) is consistent with the DLA (≈10% solar), suggesting that the neutral gas envelope is perturbed ISM gas. This study showcases the impact of dwarf–dwarf interactions on the physical and chemical state of neutral gas outside of star-forming regions. In the SKA era, joint UV and H I 21 cm analyses will be critical for connecting the cosmic neutral gas content to galaxy environments.

79 ASTRONOMY AND ASTROPHYSICS↗