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We report the results of the deepest search to date for dwarf galaxies around NGC 3109, a barred spiral galaxy with a mass similar to that of the Small Magellanic Cloud (SMC), using a semiautomated search method. Using the Dark Energy Camera, we survey a region covering a projected distance of ∼70 kpc of NGC 3109 (D = 1.3 Mpc, Rvir ∼ 90 kpc, M ∼ 108M*) as part of the MADCASH and DELVE-DEEP programs. We introduce a newly developed semiresolved search method, used alongside a resolved search, to identify crowded dwarf galaxies around NGC 3109. Using both approaches, we successfully recover the known satellites Antlia and Antlia B. We identified a promising candidate, which was later confirmed to be a background dwarf through deep follow-up observations. Our detection limits are well defined, with the sample ∼80% complete down to MV ∼ −8.0, and include detections of dwarf galaxies as faint as MV ∼ −6.0. This is the first comprehensive study of a satellite system through resolved stars around an SMC mass host. Our results show that NGC 3109 has more bright (MV ∼ −9.0) satellites than the mean predictions from cold dark matter models, but well within the host-to-host scatter. A larger sample of LMC/SMC-mass hosts is needed to test whether or not the observations are consistent with current model expectations.

We present detailed chemical abundances of the brightest star in each of the ultrafaint dwarf galaxies Eridanus IV and Centaurus I using high-resolution Magellan/MIKE spectroscopy. The brightest star in Centaurus I, CenI-5136, is a very metal-poor star with metallicity [Fe/H] = −2.52 ± 0.17 and chemical abundances typical of a star in an ultrafaint dwarf galaxy. We confirm that the star in Eridanus IV, EriIV-9808, is extremely metal poor ([Fe/H] = −3.25 ± 0.19) and find that it is carbon enhanced ([C/Fe] = 1.07 ± 0.34), as is common for many stars at this metallicity. Both stars are also neutron-capture deficient, which is typical of stars in ultrafaint dwarf galaxies, but less common in other environments. We consider possible enrichment scenarios for EriIV-9808 and tentatively conclude that it is unlikely to be the descendant of a single Population III progenitor, despite its carbon enhancement and low metallicity.

We present deep Magellan+Megacam imaging of Centaurus I (Cen I) and Eridanus IV (Eri IV), two recently discovered Milky Way ultrafaint satellites. Our data reach ∼2–3 mag deeper than the discovery data from the DECam Local Volume Exploration Survey. We use these data to constrain their distances, structural properties (e.g., half-light radii, ellipticity, and position angle), and luminosities. We investigate whether these systems show signs of tidal disturbance and identify new potential member stars using Gaia EDR3. Our deep color–magnitude diagrams show that Cen I and Eri IV are consistent with an old (τ ∼ 13.0 Gyr) and metal-poor ([Fe/H] ≤ −2.2) stellar population. We find Cen I to have a half-light radius of rh=2.′60±0.′30 (90.6 ± 11 pc), an ellipticity of ϵ = 0.36 ± 0.05, a distance of D = 119.8 ± 4.1 kpc (m − M = 20.39 ± 0.08 mag), and an absolute magnitude of MV = −5.39 ± 0.19. Similarly, Eri IV has rh=3.′24±0.′48 (65.9 ± 10 pc), ϵ = 0.26 ± 0.09, D = 69.9 ± 3.6 kpc (m − M = 19.22 ± 0.11 mag), and MV = −3.55 ± 0.24. These systems occupy a space on the size–luminosity plane consistent with other known Milky Way dwarf galaxies, which supports the findings from our previous spectroscopic follow-up. Cen I has a well-defined morphology that lacks any clear evidence of tidal disruption, whereas Eri IV hosts a significant extended feature with multiple possible interpretations.

We present deep optical observations of the stellar halo of NGC 300, an LMC-mass galaxy, acquired with the DEEP subcomponent of the DECam Local Volume Exploration survey using the 4 m Blanco Telescope. Our resolved star analysis reveals a large, low surface brightness stellar stream (MV ∼ −8.5; [Fe/H] = −1.4 ± 0.15) extending more than 40 kpc north from the galaxy’s center. We also find other halo structures, including potentially an additional stream wrap to the south, which may be associated with the main stream. The morphology and derived low metallicities of the streams and shells discovered surrounding NGC 300 are highly suggestive of a past accretion event. Assuming a single progenitor, the accreted system is approximately Fornax-like in luminosity, with an inferred mass ratio to NGC 300 of approximately 1:15. We also present the discovery of a metal-poor globular cluster (GC) (Rproj = 23.3 kpc; MV = −8.99 ± 0.16; [Fe/H] ≈ −1.6 ± 0.6) in the halo of NGC 300, the furthest identified GC associated with NGC 300. The stellar structures around NGC 300 represent the richest features observed in a Magellanic Cloud analog to date, strongly supporting the idea that accretion and subsequent disruption is an important mechanism in the assembly of dwarf galaxy stellar halos.

The metallicity distribution function and internal chemical variations of a galaxy are fundamental to understand its formation and assembly history. In this work, we analyze photometric metallicities for 3883 stars over seven half-light radii (\\(\\rm r_h\\)) in the Sculptor dwarf spheroidal (Scl dSph) galaxy, using new narrow-band imaging data from the Mapping the Ancient Galaxy in CaHK (MAGIC) survey conducted with the Dark Energy Camera (DECam) at the 4-m Blanco Telescope. This work demonstrates the scientific potential of MAGIC using the Scl dSph galaxy, one of the most well-studied satellites of the Milky Way. Our sample ranges from \\(\\rm [Fe/H] \\approx - 4.0\\) to \\(\\rm [Fe/H] \\approx - 0.6\\), includes six new extremely metal-poor candidates (\\(\\rm [Fe/H] \\leq -3.0\\)), and is almost three times larger than the largest spectroscopic metallicity dataset in the Scl dSph. Our spatially unbiased sample of metallicities provides a more accurate representation of the metallicity distribution function, revealing a more metal-rich peak than observed in the most recent spectroscopic sample. It also reveals a break in the metallicity gradient, with a strong change in the slope: from \\(-3.26 \\pm 0.18 \\rm \\ dex/deg\\) for stars inside \\(\\sim 1\\ \\rm r_h\\) to \\(-0.55 \\pm 0.26 \\rm \\ dex/deg\\) for the outer part of the Scl dSph. Our study demonstrates that combining photometric metallicity analysis with the wide field of view of DECam offers an efficient and unbiased approach for studying the stellar populations of dwarf galaxies in the Local Group.

We present detailed chemical abundances of the brightest star in each of the ultra-faint dwarf galaxies Eridanus IV and Centaurus I using high-resolution Magellan/MIKE spectroscopy. The brightest star in Centaurus I, CenI-5136, is a very metal-poor star with metallicity [Fe/H] = \\(-2.52\\pm0.17\\) and chemical abundances typical of a star in an ultra-faint dwarf galaxy. We confirm that the star in Eridanus IV, EriIV-9808, is extremely metal-poor ([Fe/H] = \\(-3.25\\pm0.19\\)) and find that it is carbon-enhanced, with [C/Fe] = \\(1.07\\pm0.34\\), as is common for many stars at this metallicity. Both stars are also neutron-capture deficient, which is typical of stars in ultra-faint dwarf galaxies, but less common in other environments. We consider possible enrichment scenarios for EriIV-9808 and tentatively conclude that it is unlikely to be the descendant of a single Pop III progenitor, despite its carbon-enhancement and low metallicity.

We present deep Magellan\\(+\\)Megacam imaging of Centaurus I (Cen I) and Eridanus IV (Eri IV), two recently discovered Milky Way ultra-faint satellites. Our data reach \\(\\sim2-3\\) magnitudes deeper than the discovery data from the DECam Local Volume Exploration (DELVE) Survey. We use these data to constrain their distances, structural properties (e.g., half-light radii, ellipticity, and position angle), and luminosities. We investigate whether these systems show signs of tidal disturbance, and identify new potential member stars using Gaia EDR3. Our deep color-magnitude diagrams show that Cen I and Eri IV are consistent with an old (\\(\\tau\\sim 13.0\\) Gyr) and metal-poor (\\(\\text{[Fe/H]}\\le-2.2\\)) stellar population. We find Cen I to have a half-light radius of \\(r_{h}=2.60\\pm0.30'\\) (\\(90.6\\pm11\\) pc), an ellipticity of \\(\\epsilon=0.36\\pm0.05\\), a distance of \\(D=119.8\\pm4.1\\) kpc (\\(m-M=20.39\\pm0.08\\) mag), and an absolute magnitude of \\(M_{V}=-5.39\\pm0.19\\). Similarly, Eri IV has \\(r_{h}=3.24\\pm0.48'\\) (\\(65.9\\pm10\\) pc), \\(\\epsilon=0.26\\pm0.09\\), \\(D=69.9\\pm3.6\\) kpc (\\(m-M=19.22\\pm0.11\\) mag), and \\(M_{V}=-3.55\\pm0.24\\). These systems occupy a space on the size-luminosity plane consistent with other known Milky Way dwarf galaxies which supports the findings from our previous spectroscopic follow-up. Cen I has a well-defined morphology which lacks any clear evidence of tidal disruption, whereas Eri IV hosts a significant extended feature with multiple possible interpretations.

Crater II (CraII), a large and low-density dwarf spheroidal galaxy, has unusual observed properties that are difficult to reproduce in cold dark matter simulations. Ongoing tidal disruption may help explain the discrepancies, as evidenced by the recent discovery of tidal tails. Here we present metallicity-sensitive narrowband photometry of the Ca II H and K lines from the Dark Energy Camera, covering \\(128\\) deg\\(^2\\) across the center and identified tidal tails of CraII as part of the Mapping the Ancient Galaxy in CaHK (MAGIC) survey. Our combined photometric metallicity, color-magnitude, proper motion, and parallax selections identify 162 CraII candidates. Of these, 37 candidates are located in the tidal tails which extend at least \\(7^\\circ\\) (\\(\\sim 95\\) kpc) from the center of CraII, suggesting it has lost \\(\\gtrsim 25\\)% of its initial stellar mass. We confirm low contamination rates with dedicated control fields and highlight the extremely low surface brightness stellar features that can be uncovered with CaHK data, as faint as \\(\\sim 36\\) mag arcsec\\(^{-2}\\). We also make the first detection of a metallicity gradient (\\(-0.34\\pm0.17~{\\rm dex}~{\\rm deg}^{-1}\\)) in the center of the galaxy and infer a stream width of \\(w\\sim 0.8^\\circ\\), roughly 50% larger than the CraII half-light radius. The detection of candidates in the most distant CraII pointings from its center implies that the tidal tails extend beyond our footprint. We compare the CraII stream to \\(N\\)-body models with \"cored\" and \"cuspy\" dark matter halo progenitors, determining that CraII's density profile is still ambiguous and warrants further modeling.

We report the first comprehensive census of the satellite dwarf galaxies around NGC 55 (\\(2.1\\) Mpc) as a part of the DECam Local Volume Exploration DEEP (DELVE-DEEP) survey. NGC 55 is one of four isolated, Magellanic analogs in the Local Volume around which DELVE-DEEP aims to identify faint dwarfs and other substructures. We employ two complementary detection methods: one targets fully resolved dwarf galaxies by identifying them as stellar over-densities, while the other focuses on semi-resolved dwarf galaxies, detecting them through shredded unresolved light components. As shown through extensive tests with injected galaxies, our search is sensitive to candidates down to \\(M_V \\lesssim -6.6\\) and surface brightness \\(\\mu \\lesssim 28.5\\) mag arcsec\\(^{-2}\\), and \\(\\sim 80\\%\\) complete down to \\(M_V \\lesssim -7.8\\). We do not report any new confirmed satellites beyond two previously known systems, ESO 294-010 and NGC 55-dw1. We construct the satellite luminosity function of NGC 55 and find it to be consistent with the predictions from cosmological simulations. As one of the first complete luminosity functions for a Magellanic analog, our results provide a glimpse of the constraints on low-mass-host satellite populations that will be further explored by upcoming surveys, such as the Vera C. Rubin Observatory's Legacy Survey of Space and Time.

We present deep optical observations of the stellar halo of NGC 300, an LMC-mass galaxy, acquired with the DEEP sub-component of the DECam Local Volume Exploration survey (DELVE) using the 4 m Blanco Telescope. Our resolved star analysis reveals a large, low surface brightness stellar stream (\\(M_V-8.5\\); [Fe/H] \\(= -1.40.15\\)) extending more than 40 kpc north from the galaxy's center. We also find other halo structures, including potentially an additional stream wrap to the south, which may be associated with the main stream. The morphology and derived low metallicities of the streams and shells discovered surrounding NGC 300 are highly suggestive of a past accretion event. Assuming a single progenitor, the accreted system is approximately Fornax-like in luminosity, with an inferred mass ratio to NGC 300 of approximately \\(1:15\\). We also present the discovery of a metal-poor globular cluster (\\(R_proj=23.3\\)~kpc; \\(M_V=-8.990.16\\); [Fe/H] \\(-1.60.6\\)) in the halo of NGC 300, the furthest identified globular cluster associated with NGC 300. The stellar structures around NGC 300 represent the richest features observed in a Magellanic Cloud analog to date, strongly supporting the idea that accretion and subsequent disruption is an important mechanism in the assembly of dwarf galaxy stellar halos.