Abstract We present new Hubble Space Telescope (HST) imaging of three recently discovered star-forming dwarf galaxies beyond the Local Group: Pavo, Corvus A, and Kamino. The discovery of Kamino is reported here for the first time. They rank among the most isolated faint dwarf galaxies known; hence they provide unique opportunities to study galaxy evolution at the smallest scales, free from the environmental effects of more massive galaxies. Our HST data reach ∼2–4 magnitudes below the tip of the red giant branch (TRGB) for each dwarf, allowing us to measure their distances, structural properties, and recent star formation histories (SFHs). All three galaxies contain a complex stellar population of young and old stars, and are typical of field galaxies in this mass regime ( M V = −10.62 ± 0.08 and D = 2.1 6 − 0.07 + 0.08 Mpc for Pavo, M V = −10.91 ± 0.10 and D = 3.34 ± 0.11 Mpc for Corvus A, and M V = −12.02 ± 0.12 and D = 6.5 0 − 0.11 + 0.15 Mpc for Kamino). Our HST-derived SFHs reveal differences among the three dwarfs: Pavo and Kamino show relatively steady, continuous star formation, while Corvus A formed ∼60% of its stellar mass by 10 Gyr ago. These results align with theoretical predictions of diverse evolutionary pathways for isolated low-mass galaxies.

Abstract SBS 0335-052E is a young star-forming dwarf galaxy with a total stellar mass of M * ≲ 10 8 M ⊙ and an extremely low metallicity ( Z ∼ 1/40 Z ⊙ ), which has long been considered to be devoid of an active galactic nucleus (AGN). Here, we report the detection of temporal flux variability of SBS 0335-052E in near-infrared (NIR) 3–4 μ m bands on timescales of several years, showing dimming and brightening of up to 50% over 14 yr, based on archival data from the Wide-field Infrared Survey Explorer. Our spectral energy distribution (SED) fitting of archival ultraviolet (UV)-NIR photometry, including AGN SED models, indicates that the variable NIR emission arises from an edge-on AGN dust torus. The UV-optical emission from the accretion disk is obscured and does not reach us, leading to the dominance of the host galaxy’s young stellar population in the UV-optical wavelengths. This analysis favors the presence of a Compton-thick, heavily obscured AGN in SBS 0335-052E, consistent with its observed X-ray weakness. From the SED fitting, we estimate an AGN bolometric luminosity of L bol = 1.2 × 10 43 erg s −1 , which implies a black hole (BH) mass of M BH ≃ 10 5 M ⊙ if the AGN is accreting at the Eddington limit. If confirmed, SBS 0335-052E would be the least massive galaxy known to host an AGN, likely harboring an intermediate-mass BH.

Interactions and mergers possibly enhance the star formation in dwarf galaxies in a group environment. We aim to study star-forming regions and the spectral energy distribution of two possibly interacting galaxies, PGC 56121 and PGC 56125, in the Hickson Compact Group 77. We utilized the far-ultraviolet (FUV) channel of the Ultra Violet Imaging Telescope (UVIT) on board AstroSat to observe and produce FUV images of the galaxies. Our FUV images are at a much higher resolution in comparison to those obtained from previous galaxy surveys by GALEX in the near-UV and those from PS-1, DSS. We have identified several star-forming regions in the two possibly interacting galaxies, PGC 56121 and PGC 56125. These two galaxies form a pair widely separated in redshift and are seen in projection. We also report the presence of a candidate tidal dwarf galaxy at the end of one of the tidal tails located to the east of the pair, and we identified three major star-forming regions in the tidal dwarf. The spectral energy distribution of three galaxies in the system is presented and analyzed to investigate the key physical properties, such as stellar mass, dust mass, total luminosity, and star formation history, of the three galaxies. Based on these observations and on a comparison with observations in radio, these three galaxies are probably part of a small group of interacting galaxies.

Abstract In dwarf galaxy models, outflows expel metal-enriched interstellar medium (ISM) into the circumgalactic medium (CGM) to reproduce their observed low metallicities, but measurements of dwarf CGM properties are scarce. We present a study of the CGM of an isolated dwarf at z = 0.5723 with a stellar mass of ≈5 × 10 7 M ⊙ and star formation rate (≈0.05 M ⊙ yr −1 ) and ISM metallicity ([O/H] ≈ −0.9) consistent with the star-forming main sequence and mass–metallicity relation. A background quasar sight line with archival UV spectra probes the dwarf’s CGM at a projected distance of 28 kpc, corresponding to approximately half of the estimated virial radius. The dwarf’s CGM is detected in H i; intermediate metal ions of C iii , O iii , O iv , and S v ; and kinematically broader, highly ionized O vi but is undetected in N iv and Ne viii . Photoionization modeling of the intermediate ions indicates a modest volume filling factor (∼6% along the sight line or ∼2% globally) and a mass of ∼2 × 10 8 M ⊙ , ∼4× higher than the dwarf’s stellar mass but ∼10× less than the highly ionized CGM. The O vi kinematics are comparable to the dwarf’s estimated virial velocity, suggesting that it is likely associated with cool, photoionized, and volume-filling CGM, with bulk motion or turbulence dominating over thermal pressure. The metallicity inferred for the intermediate ions is [O/H] = −0.6, but with low relative abundances of [C/O] = −0.6 and [N/O] < −1.0. The [N/O] is below levels expected of the dwarf’s ISM but consistent with core-collapse supernova ejecta, suggesting that supernova-enriched gas escaped the dwarf without mixing significantly with ISM enriched in nitrogen from evolved, low-mass stars.

Abstract We report the milliarcsecond localization of a high (∼1379 pc cm −3 ) dispersion measure (DM) repeating fast radio burst (FRB), FRB 20190417A. Combining European VLBI Network detections of five repeat bursts, we confirm the FRB’s host to be a low-metallicity, star-forming dwarf galaxy at z = 0.12817, similar to the hosts of FRB 20121102A, FRB 20190520B, and FRB 20240114A. We also confirm that it is associated with a previously reported persistent radio source (PRS), which is compact on milliarcsecond scales. Visibility-domain model fitting constrains the transverse physical size of the PRS to <23 pc and yields an integrated flux density of 190 ± 40 μ Jy at 1.4 GHz. Though we do not find significant evidence for DM evolution, FRB 20190417A exhibits a time-variable rotation measure (RM) ranging between +3958 ± 11 rad m −2 and +5061 ± 24 rad m −2 over a 50-day period. We find no evidence for intervening galaxy clusters in the FRB’s line of sight and place a conservative lower limit on the rest-frame host DM contribution of 1228 pc cm −3 (90% confidence)—the largest known for any FRB so far. This system strengthens the emerging picture of a rare subclass of repeating FRBs with large and variable RMs, above-average host DMs, and luminous PRS counterparts in metal-poor dwarf galaxies. Our results suggest that these systems are the result of environmental selection, or a distinct engine for FRB emission.

Abstract We present a spatially resolved analysis of the molecular star formation law (SFL) and gravitational instability in a sample of nearby dwarf galaxies (NGC 1035, NGC 4310, NGC 4451, NGC 4701, NGC 5692, and NGC 6106), using high-resolution 12 CO ( J = 1 → 0) data from the Atacama Large Millimeter/submillimeter Array. We estimate the star formation rate (SFR) by combining the Galaxy Evolution Explorer near-ultraviolet and the Wide-field Infrared Survey Explorer 12 μ m imaging data to examine the relationship between molecular gas and SFR densities on scales of several hundred parsecs. We find that the power-law slope of the molecular SFL ranges from 0.62 to 1.08, with an average value of N = 0.81 ± 0.18, increasing to N = 0.87 ± 0.05 when excluding galaxies with poorly constrained CO data. These results are roughly consistent with values observed in massive spiral galaxies, suggesting a universal molecular SFL when analyzed with sufficient resolution and sensitivity. Radial profiles of the Toomre Q parameter remain close to unity across the disks, with minimal radial variation, consistent with a self-regulated star formation model. Our results suggest that, despite their lower mass and metallicity, star formation in dwarf galaxies is governed by the same fundamental physical processes as in larger systems. This highlights the significance of high-resolution molecular gas observations in low-mass galaxies.

KK 153 is a star-forming dwarf galaxy that has been recently proposed as a new member of the sparsely populated class of gas-rich ultra-faint dwarfs that lie in the outskirts of the Local Group. We used the Large Binocular Telescope under sub-arcsec seeing conditions to resolve the outer regions of KK 153 into individual stars for the first time, reaching the red giant branch. The magnitude of the red giant branch tip was used to measure a distance of D=3.06^ +0.17 _ -0.14 Mpc, which is much more accurate and precise than the estimate previously available in the literature, based on the baryonic Tully-Fisher relation (D=2.0^ +1.7 _ -0.8 Mpc). The new distance places KK 153 clearly beyond the boundaries of the Local Group, and, together with a new measurement of the integrated magnitude, implies a stellar mass of $ ̊m M_⋆ =2.4 ± 0.2 $. The dwarf populates the extreme low-mass tail of the M_⋆ distribution of gas-rich galaxies but it is significantly more massive than the faintest local gas-rich dwarfs, Leo T and Leo P. In an analogy with similar systems, the star formation history of KK 153 may have been impacted by the re-ionisation of the Universe while keeping a sufficient gas reservoir to form new stars several Gigayear later. 10^6 ̊m M_

Low-metallicity stellar populations are very abundant in the Universe, either as the remnants of the past history of the Milky Way or similar spiral galaxies, or the young low-metallicity stellar populations that are being observed in the local dwarf galaxies or in the high-z objects with low metal content recently found with JWST. Our goal is to develop new high-spectral-resolution models tailored for low-metallicity environments and apply them to the analysis of stellar population data, particularly in cases in which a significant portion of the stellar content exhibits low metallicity. We used the state-of-the-art stellar population synthesis code HR-pyPopStar with available stellar libraries to create a new set of models focused on low-metallicity stellar populations. We compared the new spectral energy distributions with the previous models of HR-pyPopStar for solar metallicity. Once we verified that the spectra, except for the oldest ones that show some differences in the molecular bands of the TiO and G band, are similar, we re-analysed the high-resolution data from the globular cluster M 15 by finding a better estimate of its age and metallicity. Finally, we analysed a sub-sample of mostly star-forming dwarf galaxies from the MaNGA survey, we found a similar stellar mass-mean stellar metallicity weighted by light to other studies that studied star-forming dwarf galaxies and a slightly higher mean stellar metallicity than the other works that analysed all types of dwarf galaxies at the same time, but that are within the error bars.

Context. Chemically homogeneously evolving stars have been proposed to account for several exotic phenomena, including gravitational-wave emissions, gamma-ray bursts and certain types of supernovae. Aims. Here we study whether these stars can explain the observations of the metal-poor star-forming dwarf galaxy, I Zwicky 18. Methods. We apply our synthetic spectral models from Paper II to (i) establish a classification sequence for these hot stars, (ii) predict the photonionizing flux and the strength of observable emission lines from a I Zw 18-like stellar population, and (iii) compare our predictions to all available observations of this galaxy. Results. Adding two new models computed with PoWR , we report that (i) these stars follow a unique sequence of classes: O → WN → WO (i.e. without ever being WC). From our population synthesis with standard assumptions, we predict that (ii) the source of the UV C IV λ 1550 Å and other emission bumps is a couple of dozen WO-type Wolf–Rayet stars (not WC as previously assumed) which are the result of chemically homogeneous evolution, while these, combined with the rest of the O-star population, account for the high He II ionizing flux and the spectral hardness. Contrasting our results against published optical and UV data from the literature and accounting for different aperture sizes and spatial regions probed by the observations, we find that (iii) our models are highly consistent with existing measurements. Conclusions. Since our “massive Pop II stars” might just as well exist in early star-forming regions, our findings have implications for upcoming James Webb Space Telescope (JWST) surveys: the first galaxies in the high-redshift Universe may also experience the extra contribution of UV photons and the kinds of exotic explosions that chemically homogeneous stellar evolution predicts. Given that our results apply for binary populations too as long as the same fraction (10%) of the systems evolves chemically homogeneously, we conclude that the stellar progenitors of gravitational waves may very well exist today in I Zw 18.

Abstract We present the results of H i line observations towards 26 Active Galactive Nuclei (AGN)-hosting and one star-forming dwarf galaxies (M* < 109.5 M⊙) with the 19-beam spectral line receiver of FAST at 1.4 GHz. Our FAST observed targets are combined with other AGN-hosting dwarf galaxies covered in the ALFALFA footprint to form a more comprehensive sample. Utilizing the information from optical surveys, we further divide them into isolated and accompanied subsamples by their vicinity of nearby massive galaxies. We compare the H i gas abundance and star-forming rate (SFR) between the subsamples to assess the role of internal and external processes that may regulate the gas content in dwarf galaxies. As a result, we find that AGN are more commonly identified in accompanied dwarf galaxies than in their isolated counterparts. Meanwhile, AGN-hosting dwarf galaxies have slightly but significant lower H i mass fraction relatively to the non-AGN control sample in accompanied dwarf galaxies. On the other hand, we find a decreasing SFR in AGN-hosting dwarf galaxies towards denser environments, as well as an extremely low incidence of quenched isolated dwarfs within both AGN and non-AGN subsamples. These results indicate that although these AGN could potentially regulate the gas reservoir of dwarf galaxies, environmental effects are likely the dominant quenching mechanism in the low-mass universe.

Abstract We present 0.6–3.2 pc resolution mid-infrared (MIR) JWST images at 7.7 μm (F770W) and 21 μm (F2100W) covering the main star-forming regions of two of the closest star-forming low-metallicity dwarf galaxies, NGC 6822 and Wolf–Lundmark–Melotte (WLM). The images of NGC 6822 reveal filaments, edge-brightened bubbles, diffuse emission, and a plethora of point sources. By contrast, most of the MIR emission in WLM is pointlike, with a small amount of extended emission. Compared to solar-metallicity galaxies, the ratio of 7.7 μm intensity ( I ν F770W ), tracing polycyclic aromatic hydrocarbons (PAHs), to 21 μm intensity ( I ν F2100W ), tracing small, warm dust grain emission, is suppressed in these low-metallicity dwarfs. Using Atacama Large Millimeter/submillimeter Array CO(2–1) observations, we find that detected CO intensity versus I ν F770W at ≈2 pc resolution in dwarfs follows a similar relationship to that at solar metallicity and lower resolution, while the CO versus I ν F2100W relationship in dwarfs lies significantly below that derived from solar-metallicity galaxies at lower resolution, suggesting more pronounced destruction of CO molecules at low metallicity. Finally, adding in Local Group L-Band Survey 21 cm H i observations from the Very Large Array, we find that I ν F2100W and I ν F770W versus total gas ratios are suppressed in NGC 6822 and WLM compared to solar-metallicity galaxies. In agreement with dust models, the level of suppression appears to be at least partly accounted for by the reduced galaxy-averaged dust-to-gas and PAH-to-dust mass ratios in the dwarfs. Remaining differences are likely due to spatial variations in dust model parameters, which should be an exciting direction for future work in local dwarf galaxies.

Abstract To investigate the star-forming process in nearby dwarf galaxies, we present integral field unit observations of the star-forming dwarf galaxy NGC 1522 with the Very Large Telescope/Multi Unit Spectroscopic Explorer as a part of the Dwarf Galaxy Integral Survey. Our observations reveal the presence of a star-forming clumpy ring in its central region. We identify nine distinct star-forming clumps based on an extinction-corrected Hα emission line map, with a total star formation rate of about 0.1 M ⊙ yr−1. The nine clumps are considered to be starbursts, which represent an extreme case in the local Universe, without invoking major merging. We investigate the properties of ionized gas using the strong emission lines and “BPT” diagrams, in conjunction with velocity mapping. Our analysis unveils intriguing patterns, including a positive metallicity gradient and low N/O abundance ratio. This peculiar distribution of metallicity may signify external gas accretion. Our results suggest that the ongoing star formation in NGC 1522 might be triggered and sustained by the inflow of external metal-poor gas.

Context. Galaxy mergers are pivotal events in the evolutionary history of galaxies, with their impact believed to be particularly significant in dwarf galaxies due to their low masses. However, these events remain largely underexplored, especially in pristine environments such as voids. Aims. In this work, we report the serendipitous identification of an isolated merging dwarf system with a total stellar mass of M★∼109.7 M⊙, located in the centre of a cosmic void. This system is one of the rare examples, and possibly the first, of merging dwarf galaxy pairs studied within the central region of a cosmic void. This system is remarkable due to its orientation relative to the line of sight and its unique local and large-scale environment. Methods. Using CAVITY PPAK-IFU data combined with deep optical broadband imaging from the Isaac Newton Telescope, we analysed the kinematics and ionised gas properties of each dwarf galaxy in the system by employing a full spectral fitting technique. Results. The orientation of this merging pair relative to the line of sight allowed us to determine the dynamical mass of each component, which we found to have similar dynamical masses within galactocentric distances of up to 2.9 kpc. These galaxies were likely star-forming dwarfs with rotating discs prior to the merger. While the gas-phase metallicity of both components is consistent with that of star-forming dwarf galaxies, the star formation rates observed in both components exceed those typically reported for equally massive star-forming dwarf galaxies. This indicates that the merger has presumably contributed to enhancing star formation. Our analysis shows no signs of AGN activity in this merging pair. Furthermore, we found no significant difference in the optical g-r colour of this merging pair compared to other merging dwarf pairs across different environments. Conclusions. While most merging events occur in group-like environments with a high galaxy density and the tidal influence of a host halo, and isolated mergers typically involve galaxies with significant mass differences, the identified merging pair does not follow these patterns. We speculate that the global dynamics of the void or past three-body encounters involving components of this pair and a nearby dwarf galaxy might have triggered this merging event.

Baryonic cycling is reflected in the spatial distribution of metallicity within galaxies; however, gas-phase metallicity distribution and its connection with other properties of dwarf galaxies are largely unexplored. We present the first systematic study of radial gradients of gas-phase metallicities for a sample of 55 normal nearby star-forming dwarf galaxies (stellar mass M⋆ ranging from 107 to 109.5 M⊙) based on MUSE wide-field spectroscopic observations. We find that the metallicity gradient has a significant negative correlation (Spearman’s rank correlation coefficient r ≃ −0.56) with M⋆, which is in contrast with the flat or even positive correlation observed for higher-mass galaxies. The negative correlation is accompanied by a stronger central suppression of metallicity compared to the outskirts in lower-mass galaxies. Among the other explored galaxy properties, including baryonic mass, star formation distribution, galaxy environment, regularity of gaseous velocity field, and effective yield of metals yeff, only the regularity of gaseous velocity field and yeff have residual correlation with metallicity gradient after controlling for M⋆, in the sense that galaxies with an irregular velocity field or lower yeff favor a less negative or more positive metallicity gradient. Particularly, a linear combination of logarithmic stellar mass and yeff significantly improves the correlation with metallicity gradients (r ∼ −0.68) compared to using stellar mass alone. The lack of correlation with environment disproves gas accretion as a relevant factor shaping the metallicity distribution. The correlation with both gaseous velocity field regularity and yeff implies the importance of stellar feedback-driven metal redistribution within the ISM. Our finding suggests that the metal mixing and transport process, including but not limited to feedback-driven outflow, are more important than in situ metal production in shaping the metallicity distribution of dwarf galaxies.

Abstract Recent JWST observations have revealed that dwarf galaxies start to cease star formation at redshifts z > 1, yet the quenching process remains unclear. In this study, we selected a large sample of 3405 dwarf galaxies with stellar masses below 109.5 M ⊙ and redshifts ranging from 1.0 to 1.5 across all five CANDELS fields. By utilizing multi-wavelength imaging data from both JWST and HST, we examined the growth patterns and modes of star formation quenching in dwarf galaxies during the cosmic noon era. Based on their specific star formation rates (sSFR), we categorized the sample into three subgroups: star-forming dwarf galaxies below and above the star formation main sequence (SFMS), and quiescent dwarf galaxies. To analyze the UVJ color profiles of these three subgroups of dwarf galaxies, we applied the image stacking technique. This method improves the signal-to-noise ratio and extends the color profiles to the outer regions of the galaxies. Our results show that these galaxies generally exhibit nearly flat stacked color profiles, suggesting that, on average, their growth and star formation quenching patterns are self-similar, differing from those previously observed in dwarf galaxies at lower redshifts. We further discuss the potential roles of internal and external physical processes in the star formation quenching of dwarf galaxies during the cosmic noon period.

Abstract We present the star formation histories (SFHs) of 10 metal-poor (≲12% Z ⊙), star-forming dwarf galaxies from the Local Ultraviolet to Infrared Treasury survey. The derived SFHs exhibit significant variability, consistent with the irregular star formation expected for dwarf galaxies. Using synthetic near-ultraviolet (UV) and optical color–magnitude diagrams (CMDs) with various yet targeted configurations for dust and input SFHs, we quantitatively demonstrate that simultaneous modeling of the UV and optical CMDs (“UVopt” case) improves the precision of SFH measurements in recent time bins up to ∼1 Gyr, compared to the classical single optical CMD modeling (“Opt-only” case). The UVopt case reduces uncertainties relative to the Opt-only case by ∼4%–8% over the past 10 Myr, ∼8%–20% over 100 Myr, and ∼8%–14% over 1 Gyr, across various dust configurations and input SFHs. Additionally, we demonstrate discrepancies in stellar models for blue core helium-burning (BHeB) stars at the low-metallicity regime. This discrepancy can artificially inflate star formation rate (SFR) estimates in younger age bins by misinterpreting the evolved BHeB stars as reddened upper main-sequence (MS) stars. Incorporating UV data improves BHeB-MS separation and mitigates the limitations of current low-metallicity stellar models. Comparisons of the UVopt SFHs with Hα and far-UV (FUV)-based SFRs reconfirm that Hα is an unreliable tracer over its nominal 10 Myr timescale for low-SFR galaxies, while FUV provides a more reliable tracer but yields SFRFUV values up to twice those of CMD-based 〈SFR〉100 Myr. Our findings underscore the importance of UV data in refining recent SFHs in low-metallicity environments.

Abstract We study the physical origins of outflowing cold clouds in a sample of 14 low-redshift dwarf (M * ≲ 1010 M ⊙) galaxies from the Cosmic Origins Spectrograph Legacy Archive Spectroscopic SurveY (CLASSY) using Keck/ESI data. Outflows are traced by broad (FWHM ∼260 km s−1) and very-broad (VB; FWHM ∼1200 km s−1) velocity components in strong emission lines like [O iii] λ5007 and Hα. The maximum velocities ( v max ) of broad components correlate positively with star formation rate, unlike the anticorrelation observed for VB components, and are consistent with superbubble models. In contrast, supernova-driven galactic wind models better reproduce the v max of VB components. Direct radiative cooling from a hot wind significantly underestimates the luminosities of both broad and VB components. A multiphase wind model with turbulent radiative mixing reduces this discrepancy to at least 1 dex for most VB components. Stellar photoionization likely provides additional energy since broad components lie in the starburst locus of excitation diagnostic diagrams. We propose a novel interpretation of outflow origins in star-forming dwarf galaxies—broad components trace expanding superbubble shells, while VB components originate from galactic winds. One-zone photoionization models fail to explain the low-ionization lines ([S ii] and [O i]) of broad components near the maximal starburst regime, which two-zone photoionization models with density-bounded channels instead reproduce. These two-zone models indicate anisotropic leakage of Lyman continuum photons through low-density channels formed by expanding superbubbles. Our study highlights extreme outflows ( v max ≳ 1000 km s − 1 ) in nine out of 14 star-forming dwarf galaxies, comparable to active galactic nucleus–driven winds.

Context. At late stages, massive stars experience strong mass-loss rates, losing their external layers and thus producing a dense H-rich circumstellar medium (CSM). After the explosion of a massive star, the collision and continued interaction of the supernova (SN) ejecta with the CSM power the SN light curve through the conversion of kinetic energy into radiation. When the interaction is strong, the light curve shows a broad peak and high luminosity that lasts for several months. For these SNe, the spectral evolution is also slower compared to non-interacting SNe. Notably, energetic shocks between the ejecta and the CSM create the ideal conditions for particle acceleration and the production of high-energy (HE) neutrinos above 1 TeV. Aims. We study four strongly interacting Type IIn SNe, 2021acya, 2021adxl, 2022qml, and 2022wed, in order to highlight their peculiar characteristics, derive the kinetic energy of their explosion and the characteristics of the CSM, infer clues on the possible progenitors and their environment, and relate them to the production of HE neutrinos. Methods. We analysed spectro-photometric data of a sample of interacting SNe to determine their common characteristics and derive the physical properties (radii and masses) of the CSM and the ejecta kinetic energies and compare them to HE neutrino production models. Results. The SNe analysed in this sample exploded in dwarf star-forming galaxies, and they are consistent with energetic explosions and strong interaction with the surrounding CSM. For SNe 2021acya and 2022wed, we find high CSM masses and mass-loss rates, linking them to very massive progenitors. For SN 2021adxl, the spectral analysis and less extreme CSM mass suggest a stripped-envelope massive star as a possible progenitor. SN 2022qml is marginally consistent with being a Type Ia thermonuclear explosion embedded in a dense CSM. The mass-loss rates for all the SNe are consistent with the expulsion of several solar masses of material during eruptive episodes in the last few decades before the explosion. Finally, we find that the SNe in our sample are marginally consistent with HE neutrino production.

ABSTRACT Dwarf galaxies dominate the galaxy number density, making them critical to our understanding of galaxy evolution. However, typical dwarfs are too faint to be visible outside the very local Universe in past surveys like the SDSS, which offer large footprints but are shallow. Dwarfs in such surveys have relatively high star formation rates, which boost their luminosity, making them detectable in shallow surveys, but also biased and potentially unrepresentative of dwarfs as a whole. Here, we use deep data to perform an unbiased statistical study of $\sim$7000 nearby ($z\lt 0.25$) dwarfs (10$^8$ M$_{\odot }$ < $M_{\star }$ < 10$^{9.5}$ M$_{\odot }$) in the COSMOS field which, at these redshifts, is a relatively low-density region. At $z\sim 0.05$, $\sim$40 per cent of dwarfs in low-density environments are red/quenched, falling to $\sim$30 per cent by $z\sim 0.25$. Red dwarfs reside closer to nodes, filaments and massive galaxies. Proximity to a massive galaxy appears to be more important in determining whether a dwarf is red, rather than simply its distance from nodes and filaments or the mean density of its local environment. Interestingly, around half of the red dwarfs reside outside the virial radii of massive galaxies and around a third of those also inhabit regions in the lower 50 per cent in density percentile (i.e. regions of very low ambient density). Around half of the red dwarf population is therefore quenched by mechanisms unrelated to environment, which are likely to be internal processes such as stellar and active galactic nucleus feedback.

Abstract Ongoing large stellar spectroscopic surveys of the Milky Way seek to reconstruct the major events in the assembly history of the Galaxy. Chemical and kinematic observations can be used to separate the contributions of different progenitor galaxies to the present-day stellar halo. Here, we compute the number of progenitors that contribute to the accreted stellar halos of simulated Milky Way–like galaxies as a function of radius (the radial diversity) in three suites of models: Bullock & Johnston, Aquarius, and Auriga. We show that there are significant differences between the predictions of these three models, beyond the halo-to-halo scatter expected in ΛCDM. Predictions of diversity from numerical simulations are sensitive to model-dependent assumptions regarding the efficiency of star formation in dwarf galaxies. We compare, at face value, to current constraints on the radial diversity of the Milky Way's accreted halo. These constraints imply that the halo of our Galaxy is dominated by ∼2 progenitors in the range 8–45 kpc, in contrast to averages of 7 progenitors in the Bullock & Johnston models, 3.5 in Aquarius, and 4.2 in Auriga over the same region. We additionally find that the models with radial diversity most similar to that of the Milky Way are predominantly those with ongoing merger events. The Milky Way therefore appears unusual in having an accreted stellar halo dominated by a small number of progenitors accreted at very early times.