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Abstract We present results from Identifying Dwarfs of MC Analog GalaxiEs (ID-MAGE), a survey aimed at identifying and characterizing unresolved satellite galaxies around 35 nearby LMC- and SMC-mass hosts (D = 4−10 Mpc). We use archival DESI Legacy Survey imaging data and perform an extensive search for dwarf satellites, extending out to a radius of 150 kpc (∼R_vir). We identify 355 candidate satellite galaxies, including 264 new discoveries. Extensive tests with injected galaxies demonstrate that the survey is complete down toM_V ∼ −9.0 (assuming the distance of the host) andμ_0,V ∼ 26 mag arcsec⁻²(assuming ann = 1 Sérsic profile). We perform consistent photometry, via Sérsic profile fitting, on all candidates and have initiated a comprehensive follow-up campaign to confirm and characterize candidates. Through a systematic visual inspection campaign, we classify the top candidates as high-likelihood satellites. On average, we find 4.0 ± 1.4 high-likelihood candidate satellites per LMC-mass host and 2.1 ± 0.6 per SMC-mass host, which is within the range predicted by cosmological models. We use this sample to establish upper and lower estimates on the satellite luminosity function of LMC-/SMC-mass galaxies. ID-MAGE nearly triples the number of low-mass galaxies surveyed for satellites with well-characterized completeness limits, providing a unique data set to explore small-scale structure and dwarf galaxy evolution around low-mass hosts in diverse environments. 

Abstract The Virgo Filament Survey (VFS) is a comprehensive study of galaxies that reside in the extended filamentary structures surrounding the Virgo Cluster, out to 12 virial radii. The primary goal is to characterize all of the dominant baryonic components within galaxies and to understand whether and how they are affected by the filament environment. A key constituent of VFS is a narrowband Hαimaging survey of over 600 galaxies, VFS-Hα. The Hαimages reveal detailed, resolved maps of the ionized gas and massive star formation. This imaging is particularly powerful as a probe of environmentally induced quenching because different physical processes affect the spatial distribution of star formation in different ways. In this paper, we present the first results from the VFS-Hαfor the NGC 5364 group, a low-mass ( ${\log }_{10}(M_{\mathrm{dyn}}/M_{\odot })<13$) system located at the western edge of the Virgo III filament. We combine Hαimaging with resolved Hiobservations from MeerKAT for eight group members. These galaxies exhibit peculiar morphologies, including strong distortions in the stars and the gas, truncated Hiand Hαdisks, H itails, extraplanar Hαemission, and off-center Hαemission. These signatures are suggestive of environmental processing such as tidal interactions, ram pressure stripping, and starvation. We quantify the role of ram pressure stripping expected in this group, and find that it can explain the cases of Hitails and truncated Hαfor all but one of the disk-dominated galaxies. Our observations indicate that multiple physical mechanisms are disrupting the baryon cycle in these group galaxies. 

ABSTRACT High-redshift ($$z\sim 1$$) galaxy clusters are the domain where environmental quenching mechanisms are expected to emerge as important factors in the evolution of the quiescent galaxy population. Uncovering these initially subtle effects requires exploring multiple dependencies of quenching across the cluster environment, and through time. We analyse the stellar mass functions (SMFs) of 17 galaxy clusters within the GOGREEN and GCLASS surveys in the range $0.8< z<1.5$, and with $$\log {(M/{\rm {M_\odot }})}>9.5$$. The data are fit simultaneously with a Bayesian model that allows the Schechter function parameters of the quiescent and star-forming populations to vary smoothly with cluster-centric radius and redshift. The model also fits the radial galaxy number density profile of each population, allowing the global quenched fraction to be parametrized as a function of redshift and cluster velocity dispersion. We find the star-forming SMF to not depend on radius or redshift. For the quiescent population however, there is $$\sim 2\sigma$$ evidence for a radial dependence. Outside the cluster core ($$R>0.3\, R_{\rm 200}$$), the quenched fraction above $$\log {(M/{\rm {M_\odot }})}=9.5$$ is $$\sim 40{\rm\,\,per\, cent}$$, and the quiescent SMF is similar in shape to the star-forming field. In contrast, the cluster core has an elevated quenched fraction ($$\sim 70{\rm \,\,per\, cent}$$), and a quiescent SMF similar in shape to the quiescent field population. We explore contributions of ‘early mass-quenching’ and mass-independent ‘environmental-quenching’ models in each of these radial regimes. The core is well described primarily by early mass-quenching, which we interpret as accelerated quenching of massive galaxies in protoclusters, possibly through merger-driven feedback mechanisms. The non-core is better described through mass-independent environmental-quenching of the infalling field population. 

Abstract Using the Systematically Measuring Ultra-Diffuse Galaxies and Sloan Digital Sky Survey catalogs and our own reprocessing of the Legacy Survey imaging, we investigate the properties of nuclear star clusters (NSCs) in galaxies having central surface brightnesses as low as 27 mag arcsec⁻². We identify 273 (123 with known redshift) and 32 NSC-bearing galaxies in the two samples, respectively, where we require candidate NSCs to have a separation of less than 0.10r_efrom the galaxy center. We find that galaxies with low central surface brightness (μ_0,g> 24 mag arcsec⁻²) are more likely to contain an NSC if they (1) have a higher stellar mass, (2) have a higher stellar-to-total mass ratio, (3) have a brighter central surface brightness, (4) have a larger axis ratio, or (5) lie in a denser environment. Because of the correlations among these various quantities, it is likely that only one or two are true physical drivers. We also find scaling relations for the NSC mass with stellar mass (M_NSC/ $M_{\odot }={10}^{6.02\pm 0.03}{(M_{*,\mathrm{gal}}/{10}^8{M}_{\odot })}^{0.77\pm 0.04}$) and halo mass (M_NSC/ $M_{\odot }={10}^{6.11\pm 0.05}{(M_{h,\mathrm{gal}}/{10}^{10}{M}_{\odot })}^{0.92\pm 0.05}$), although it is the scaling with halo mass that is consistent with a direct proportionality. In galaxies with an NSC,M_NSC≈ 10⁻⁴M_h,gal. This proportionality echoes the finding of a direct proportionality between the mass (or number) of globular clusters (GCs) in galaxies and the galaxy’s total mass. These findings favor a related origin for GCs and NSCs. 

Abstract Stellar streams in the Milky Way are promising detectors of low-mass dark matter (DM) subhalos predicted by ΛCDM. Passing subhalos induce perturbations in streams that indicate the presence of the subhalos. Understanding how known DM-dominated satellites impact streams is a crucial step toward using stream perturbations to constrain the properties of dark perturbers. Here, we cross-match a Gaia Early Data Release 3 and SEGUE member catalog of the Cetus-Palca stream (CPS) with H3 for additional radial velocity measurements and fit the orbit of the CPS using this six-dimensional (6D) data. We demonstrate for the first time that the ultra-faint dwarf Segue 2 had a recent (77 ± 5 Myr ago) close flyby (within the stream's 2σwidth) with the CPS. This interaction enables constraints on Segue 2’s mass and density profile at larger radii ( $O\left(1\right)$kpc) than are probed by its stars ( $O\left(10\right)$pc). While Segue 2 is not expected to strongly affect the portion of the stream covered by our 6D data, we predict that if Segue 2’s mass within ∼ 6 kpc is 5 × 10⁹M_⊙, the CPS's velocity dispersion will be ∼ 40 km s⁻¹larger atϕ₁ > 20° than atϕ₁ < 0°. If no such heating is detected, Segue 2’s mass cannot exceed 10⁹M_⊙within ∼ 6 kpc. The proper motion distribution of the CPS near the impact site is mildly sensitive to the shape of Segue 2’s density profile. This study presents a critical test for frameworks designed to constrain properties of dark subhalos from stream perturbations. 

Abstract Recent theoretical work and targeted observational studies suggest that filaments are sites of galaxy preprocessing. The aim of the WISESize project is to directly probe galaxies over the full range of environments to quantify and characterize extrinsic galaxy quenching in the local universe. In this paper, we useGALFITto measure the IR 12μm (R₁₂) and 3.4μm (R_3.4) effective radii of 603 late-type galaxies in and surrounding the Virgo cluster. We find that Virgo cluster galaxies show smaller star-forming disks relative to their field counterparts at the 2.5σlevel, while filament galaxies show smaller star-forming disks to almost 1.5σ. Our data, therefore, show that cluster galaxies experience significant effects on their star-forming disks prior to their final quenching period. There is also tentative support for the hypothesis that galaxies are preprocessed in filamentary regions surrounding clusters. On the other hand, galaxies belonging to rich groups and poor groups do not differ significantly from those in the field. We additionally find hints of a positive correlation between stellar mass and size ratio for both rich group and filament galaxies, though the uncertainties on these data are consistent with no correlation. We compare our size measurements with the predictions from two variants of a state-of-the-art semi-analytic model (SAM), one which includes starvation and the other incorporating both starvation and ram pressure stripping (RPS). Our data appear to disfavor the SAM, which includes RPS for the rich group, filament, and cluster samples, which contributes to improved constraints for general models of galaxy quenching. 

Abstract We present our photometric search for potential nuclear star clusters (NSCs) in ultra-diffuse galaxies (UDGs) as an extension of the SMUDGes catalog. We identify 325 SMUDGes galaxies with NSCs and, from the 144 with existing distance estimates, identify 33 NSC hosts as UDGs (μ_0,g≥ 24 mag arcsec⁻²,r_e≥ 1.5 kpc). The SMUDGes with NSCs lie on the galaxy red sequence, satisfy the relationship between NSC and host galaxy stellar masses, have a mean NSC stellar mass fraction of 0.02 but reach as high as 0.1, have NSCs that are displaced from the host center with a standard deviation of 0.10r_e, and weakly favor higher-density environments. All of these properties are consistent with previous results from higher surface brightness galaxy samples, allowing for at most a relatively weak dependence of NSC behavior on host galaxy surface brightness. 

Abstract We report the discovery of Corvus A, a low-mass, gas-rich galaxy at a distance of approximately 3.5 Mpc, identified in DR10 of the Dark Energy Camera Legacy Imaging Survey during the initial phase of our ongoing SEmi-Automated Machine LEarning Search for Semi-resolved galaxies (SEAMLESS). Jansky Very Large Array observations of Corvus A detect Hiline emission at a radial velocity of 523 ± 2 km s⁻¹. Magellan/Megacam imaging reveals an irregular and complex stellar population with both young and old stars. We detect UV emission in Neil Gehrels Swift observations, indicative of recent star formation. However, there are no signs of Hiiregions in Hαimaging from Steward Observatory’s Kuiper telescope. Based on the Megacam color–magnitude diagram we measure the distance to Corvus A via the tip of the red giant branch standard candle as 3.48 ± 0.24 Mpc. This makes Corvus A remarkably isolated, with no known galaxy within ∼1 Mpc. Based on this distance, we estimate the Hiand stellar mass of Corvus A to be $\log M_{\mathrm{H}\mathrm{I}}/M_{\odot }=6.59$and $\log M_{*}/M_{\odot }=6.0$, respectively. Although there are some signs of rotation, the Hidistribution of Corvus A appears to be close to face on, analogous to that of Leo T, and we therefore do not attempt to infer a dynamical mass from its Hiline width. Higher-resolution synthesis imaging is required to confirm this morphology and to draw robust conclusions from its gas kinematics. 

Abstract To better understand the formation of large, low-surface-brightness galaxies, we measure the correlation function between ultradiffuse galaxy (UDG) candidates and Milky Way analogs (MWAs). We find that: (1) the projected radial distribution of UDG satellites (projected surface density ∝r^{−0.84±0.06}) is consistent with that of normal satellite galaxies; (2) the number of UDG satellites per MWA (S_UDG) is ∼0.5 ± 0.1 over projected radii from 20 to 250 kpc and −17 <M_r< −13.5; (3)S_UDGis consistent with a linear extrapolation of the relationship between the number of UDGs per halo versus halo mass obtained over galaxy group and cluster scales; (4) red UDG satellites dominate the population of UDG satellites (∼80%); (5) over the range of satellite magnitudes studied, UDG satellites comprise ∼10% of the satellite galaxy population of MWAs; and (6) a significant fraction of these (∼13%) have estimated total masses >10^10.9M_⊙or, equivalently, at least half the halo mass of the LMC, and populate a large fraction (∼18%) of the expected subhalos down to these masses. All of these results suggest a close association between the overall low-mass galaxy population and UDGs, which we interpret as favoring models where UDG formation principally occurs within the general context of low-mass galaxy formation over models invoking more exotic physical processes specifically invoked to form UDGs. 

ABSTRACT We present the first detailed chemical-abundance analysis of stars from the dwarf-galaxy stellar stream Wukong/LMS-1 covering a wide metallicity range ($$-3.5 \lt \rm [Fe/H] \lesssim -1.3$$). We find abundance patterns that are effectively indistinguishable from the bulk of Indus and Jhelum, a pair of smaller stellar streams proposed to be dynamically associated with Wukong/LMS-1. We confirmed a carbon-enhanced metal-poor star ($$\rm [C/Fe] \gt +0.7$$ and $$\rm [Fe/H] \sim -2.9$$) in Wukong/LMS-1 with strong enhancements in Sr, Y, and Zr, which is peculiar given its solar-level [Ba/Fe]. Wukong/LMS-1 stars have high abundances of α elements up to $$\rm [Fe/H] \gtrsim -2$$, which is expected for relatively massive dwarfs. Towards the high-metallicity end, Wukong/LMS-1 becomes α-poor, revealing that it probably experienced fairly standard chemical evolution. We identified a pair of N- and Na-rich stars in Wukong/LMS-1, reminiscent of multiple stellar populations in globular clusters. This indicates that this dwarf galaxy contained at least one globular cluster that was completely disrupted in addition to two intact ones previously known to be associated with Wukong/LMS-1, which is possibly connected to similar evidence found in Indus. From these ≥3 globular clusters, we estimate the total mass of Wukong/LMS-1 to be $${\approx }10^{10} \, \mathrm{M}_\odot$$, representing ∼1 per cent of the present-day Milky Way. Finally, the [Eu/Mg] ratio in Wukong/LMS-1 continuously increases with metallicity, making this the first example of a dwarf galaxy where the production of r-process elements is clearly dominated by delayed sources, presumably neutron-star mergers.