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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 A subset of galaxies have dense nuclei, and when these galaxies are accreted and tidally stripped, the nuclei can masquerade as globular clusters in the halos of large galaxies. If these nuclei contain massive central black holes, some may accrete gas and become observable as active galactic nuclei. Previous studies have found that candidate stripped nuclei rarely host luminous X-ray sources, but these studies were typically restricted to both the most massive candidate nuclei and the most luminous X-ray sources. Here we use new and archival Chandra and XMM-Newton data to search for X-ray emission in a near-complete sample of massive globular clusters and candidate stripped nuclei in the nearest accessible elliptical galaxy, NGC 5128. This sample has the unique advantage that the candidate stripped nuclei are identified dynamically via elevated mass-to-light ratios (M/L_V). Our central result is that 5/22 ( $23_{-6}^{+11}$%) of the candidate stripped nuclei have X-ray sources down to a typical limit ofL_X∼ 5 × 10³⁶erg s⁻¹, a fraction lower than or comparable to that among massive clusters with normalM/L_V(16/41; $39_{-7}^{+8}$%). Hence we confirm and extend the result that nearly all X-ray sources in stripped nuclei are likely to be X-ray binaries rather than active galactic nuclei. If the candidate stripped nuclei have black holes of typical masses ∼2 × 10⁵M_⊙needed to explain their elevatedM/L_V, then they have typical Eddington ratios of ≲ 2 × 10⁻⁶. This suggests that it will be challenging to conduct an accretion census of wandering black holes around even nearby galaxies. 

Abstract We present a catalog of 34 new candidate (13 high confidence) isolated, young stellar systems within the Virgo galaxy cluster identified through a citizen science search of public optical and ultraviolet imaging. “Blue blobs” are a class of blue, faint, isolated, extremely low stellar mass, and metal-rich star-forming clouds embedded in the hot intracluster medium of the Virgo cluster. Only six blue blobs were known previously and here we confirm an additional six of our candidates through velocity and metallicity measurements from follow-up optical spectroscopy on the Hobby–Eberly Telescope (HET). Our 13 high confidence candidates (including the six confirmed) have properties consistent with prior known blue blobs and are inconsistent with being low-mass galaxies. Most candidates are concentrated in relatively dense regions, roughly following filamentary structures within the cluster, but avoiding its center. Three of our candidates are likely the stellar counterparts of known “optically dark” clouds of neutral hydrogen in the cluster, while a further four are widely separated extensions to previously known blue blobs. The properties of our new candidates are consistent with previous conclusions that blue blobs likely originated from ram pressure stripping events, however, their locations in velocity–projected cluster-centric radius phase space imply that their parent galaxies are not on their first infall into the cluster. Through our ongoing follow-up program with HET we aim to confirm additional candidates, however, detailed understanding of the stellar populations and star formation histories of blue blobs will require JWST observations. 

Abstract We present optical photometry and spectroscopy of SN 2019hnl. Discovered within ∼26 hr of explosion by the ATLAS survey, SN 2019hnl is a typical Type IIP supernova (SN) with a peak absoluteV-band magnitude of −16.7 ± 0.1 mag, a plateau length of ∼107 days, and an early decline rate of 0.0086 ± 0.0006 mag (50 days)⁻¹. We use nebular spectroscopy and hydrodynamic modeling with thesnec,mesa, andstellacodes to infer that the progenitor of SN 2019hnl was anM_ZAMS ∼ 11M_⊙red supergiant, which produced 0.047 ± 0.007M_⊙of⁵⁶Ni in the explosion. As a part of our hydrodynamic modeling, we reduced hydrogen envelope mass by scaling the mass loss within the “Dutch” wind scheme to fit our light curve, showing that the progenitor of a relatively typical Type IIP SN may experience partial stripping during their evolution and establish massive (∼0.2M_⊙) circumstellar material environments prior to core collapse. 

Abstract MeerKAT observations of the recently discovered, extremely low mass galaxy Pavo have revealed a neutral gas (Hi) reservoir that was undetected in archival Hisingle dish data. We measure Pavo’s Himass as $\log M_{\mathrm{HI}}/M_{\odot }=5.79\pm 0.05$, making it the lowest mass Hireservoir currently known in an isolated galaxy (with a robust distance measurement). Despite Pavo’s extreme isolation, with no known neighbor within over 700 kpc, its Hireservoir is highly disturbed. It does not show clear signs of rotation, and its center of mass is offset from the stellar body center by 320 pc, while its peak is offset by 82 pc (both in projection). Despite this disturbed morphology, Pavo still appears to be consistent with the Hisize–mass relation, although it is not possible to accurately determine a suitable inclination correction. Such disturbed, offset, and disorganized Hireservoirs are predicted by simulations of low-mass, star-forming dwarfs in which supernova-driven outflows efficiently disrupt the interstellar medium after a star formation (SF) event. It is likely that we are witnessing Pavo in precisely this period, tens to a few hundred Myr after a SF episode, when internal feedback has disrupted its gas reservoir. 

Context.Core-collapse supernovae (CCSNe) may have contributed a significant amount of dust in the early Universe. Freshly formed coolant molecules (e.g., CO) and warm dust can be found in CCSNe as early as ∼100 d after the SN explosion, allowing the study of their evolution with time series observations. Aims.Through study of the Type II SN 2023ixf, we aim to investigate the temporal evolution of the temperature, velocity, and mass of CO and compare them with other CCSNe, exploring their implications for the dust formation in CCSNe. From observations of velocity profiles of lines of other species (e.g., H and He), we also aim to characterize and understand the interaction of the SN ejecta with preexisting circumstellar material (CSM). Methods.We present a time series of 16 near-infrared spectra of SN 2023ixf from 9 to 307 d, taken with multiple instruments: Gemini/GNIRS, Keck/NIRES, IRTF/SpeX, and MMT/MMIRS. Results.The early (t ≲ 70 d) spectra indicate interaction between the expanding ejecta and nearby CSM. Att ≲ 20 d, intermediate-width line profiles corresponding to the ejecta-wind interaction are superposed on evolving broad P Cygni profiles. We find intermediate-width and narrow lines in the spectra untilt ≲ 70 d, which suggest continued CSM interaction. We also observe and discuss high-velocity absorption features in Hαand Hβline profiles formed by CSM interaction. The spectra contain CO first overtone emission between 199 and 307 d after the explosion. We modeled the CO emission and found the CO to have a higher velocity (3000–3500 km s⁻¹) than that in Type II-pec SN 1987A (1800–2000 km s⁻¹) during similar phases (t = 199 − 307 d) and a comparable CO temperature to SN 1987A. A flattened continuum at wavelengths greater than 1.5 μm accompanies the CO emission, suggesting that the warm dust is likely formed in the ejecta. The warm dust masses are estimated to be on the order of ∼10⁻⁵ M_⊙. 

Abstract 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 $r_h=2.\prime 60\pm 0.\prime 30$(90.6 ± 11 pc), an ellipticity ofϵ= 0.36 ± 0.05, a distance ofD= 119.8 ± 4.1 kpc (m−M= 20.39 ± 0.08 mag), and an absolute magnitude ofM_V= −5.39 ± 0.19. Similarly, Eri IV has $r_h=3.\prime 24\pm 0.\prime 48$(65.9 ± 10 pc),ϵ= 0.26 ± 0.09,D= 69.9 ± 3.6 kpc (m−M= 19.22 ± 0.11 mag), andM_V= −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. 

Abstract We present and analyze the extensive optical broadband photometry of the Type II SN 2023ixf up to 1 yr after explosion. We find that, when compared to two preexisting model grids, the bolometric light curve is consistent with drastically different combinations of progenitor and explosion properties. This may be an effect of known degeneracies in Type IIP light-curve models. We independently compute a large grid ofMESA+STELLAsingle-star progenitor and light-curve models with various zero-age main-sequence masses, mass-loss efficiencies, and convective efficiencies. Using the observed progenitor variability as an additional constraint, we select stellar models consistent with the pulsation period and explode them according to previously established scaling laws to match plateau properties. Our hydrodynamic modeling indicates that SN 2023ixf is most consistent with a moderate-energy ( $E_{\exp }\approx 7\times 10^{50}$erg) explosion of an initially high-mass red supergiant progenitor (≳16.5M_⊙) that lost a significant amount of mass in its prior evolution, leaving a low-mass hydrogen envelope (≲3M_⊙) at the time of explosion, with a radius ≳950R_⊙and a synthesized⁵⁶Ni mass of ≈0.068M_⊙. We posit that previous mass transfer in a binary system may have stripped the envelope of SN 2023ixf’s progenitor. The analysis method with pulsation period presented in this work offers a way to break degeneracies in light-curve modeling in the future, particularly with the upcoming Vera C. Rubin Observatory Legacy Survey of Space and Time, when a record of progenitor variability will be more common. 

Abstract 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,R_vir∼ 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 toM_V∼ −8.0, and include detections of dwarf galaxies as faint asM_V∼ −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 (M_V∼ −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. 

Abstract We present early multiwavelength photometric and spectroscopic observations of the Type IIb supernova SN 2024uwq, capturing its shock-cooling emission phase and double-peaked light-curve evolution. Early spectra reveal broad Hα(v ∼ 15,500 km s⁻¹) and HeIP Cygni profiles of similar strengths. Over time the HeIlines increase in strength while the Hαdecreases, consistent with a hydrogen envelope (M_env = 0.7–1.35M_⊙) overlying helium-rich ejecta. Analytic modeling of early shock cooling emission and bolometric light analysis constrains the progenitor to a partially stripped star with radiusR = 10–60R_⊙, consistent with a blue/yellow supergiant with an initial zero-age main-sequence mass of 12–20M_⊙likely stripped via binary interaction. SN 2024uwq occupies a transitional position between compact and extended Type IIb supernovae, highlighting the role of binary mass transfer efficiency in shaping a continuum of stripped-envelope progenitors. Our results underscore the importance of early UV/optical observations to characterize shock breakout signatures critical to map the diversity in evolutionary pathways of massive stars. Upcoming time-domain surveys, including Rubin Observatory’s LSST and UV missions like ULTRASAT and UVEX, will revolutionize our ability to systematically capture these early signatures, probing the full diversity of stripped progenitors and their explosive endpoints.