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We present [Fe/H] values for globular clusters associated with the Fornax, Sagittarius, and Canis Major dwarf spheroidal galaxies based on the light curve properties of their ab-type RR Lyrae variables. Fornax is a classical dwarf spheroidal containing five globular clusters and exhibiting a spheroidal shape in the sky. Sagittarius and Canis Major, possess six and four globular clusters, respectively, and have both been tidally disrupted to a significant degree by the gravitational field of the Milky Way galaxy. Based on an analysis of the periods and light curve amplitudes of 76 globular cluster ab-type RR Lyraes in Fornax, 103 in Sagittarius, and 29 in Canis Major, we find mean metallicities of |$\langle$| [Fe/H] |$\rangle$| = –1.67 ± 0.05, –1.76 ± 0.12, and –1.69 ± 0.25 for the globular clusters in Fornax, Sagittarius, and Canis Major, respectively. Given the similarity of these three values, and coupled with the well-established correlation between the mean metal abundance and total luminosity for dwarf spheroidal galaxies, we conclude that the absolute V -band magnitudes of these three galaxies are indistinguishable to within ∼0.8 mag. [ABSTRACT FROM AUTHOR]

We present a hierarchical Bayesian pipeline, BP3M, that measures positions, parallaxes, and proper motions (PMs) for cross-matched sources between Hubble Space Telescope (HST) images and Gaia—even for sparse fields (N * < 10 per image)—expanding from the recent GaiaHub tool. This technique uses Gaia-measured astrometry as priors to predict the locations of sources in HST images, and is therefore able to put the HST images onto a global reference frame without the use of background galaxies/QSOs. Testing our publicly available code in the Fornax and Draco dwarf spheroidal galaxies, we measure PMs that are a median of 8–13 times more precise than Gaia DR3 alone for 20.5 < G < 21 mag. We are able to explore the effect of observation strategies on BP3M astrometry using synthetic data, finding an optimal strategy to improve parallax and position precision at no cost to the PM uncertainty. Using 1619 HST images in the sparse COSMOS field (median nine Gaia sources per HST image), we measure BP3M PMs for 2640 unique sources in the 16 < G < 21.5 mag range, 25% of which have no Gaia PMs; the median BP3M PM uncertainty for 20.25 < G < 20.75 mag sources is 0.44 mas yr−1 compared to 1.03 mas yr−1 from Gaia, while the median BP3M PM uncertainty for sources without Gaia-measured PMs (20.75 < G < 21.5 mag) is 1.16 mas yr−1. The statistics that underpin the BP3M pipeline are a generalized way of combining position measurements from different images, epochs, and telescopes, which allows information to be shared between surveys and archives to achieve higher astrometric precision than that from each catalog alone. [ABSTRACT FROM AUTHOR]

With a luminosity similar to that of Milky Way dwarf spheroidal systems like Sextans, but a spatial extent similar to that of ultra-diffuse galaxies, Andromeda (And) XIX is an unusual satellite of M31. To investigate the origin of this galaxy, we measure chemical abundances for And XIX derived from medium-resolution (R ∼ 6000) spectra from the Deep Extragalactic Imaging Multi-Object Spectrograph on the Keck II telescope. We coadd 79 red giant branch stars, grouped by photometric metallicity, in order to obtain a sufficiently high signal-to-noise ratio to measure 20 [Fe/H] and [ α /Fe] abundances via spectral synthesis. The latter are the first such measurements for And XIX. The mean metallicity we derive for And XIX places it ∼2 σ higher than the present-day stellar mass–metallicity relation for Local Group dwarf galaxies, potentially indicating it has experienced tidal stripping. A loss of gas and associated quenching during such a process, which prevents the extended star formation necessary to produce shallow [ α /Fe]–[Fe/H] gradients in massive systems, is also consistent with the steeply decreasing [ α /Fe]–[Fe/H] trend we observe. In combination with the diffuse structure and disturbed kinematic properties of And XIX, this suggests tidal interactions, rather than galaxy mergers, are strong contenders for its formation. [ABSTRACT FROM AUTHOR]

We present and discuss the results of the Giant Metrewave Radio Telescope H  i 21-cm line mapping for five isolated low-mass (M |$_{\rm bary}$| |$\sim$| (2–8) |$\times 10^7$|  M |$\odot$|⁠) eXtremely Metal Poor dwarfs [12+ |$\log$| (O/H) = 7.13–7.28], selected from the nearby void galaxy sample. All the studied void dwarfs show disturbed morphology in the H  i maps with the angular resolutions of |$\sim 11$| to |$\sim 40\,{\rm arcsec}$|⁠. We examine the H  i morphology and velocity field and the relative orientation of their stellar and gas body spins. We discuss the overall non-equilibrium state of their gas and the possible origin and evolution of the studied void dwarfs. The most straightforward interpretation of the ubiquitous phenomenon of the gas component non-equilibrium state in these and similar void dwarfs is the cold accretion from the void filaments and/or minor mergers. The cold gas accretion in voids could be linked to the presence of small filaments that constitute the substructure of voids. [ABSTRACT FROM AUTHOR]

We provide new constraints on the dark matter halo density profile of Milky Way (MW) dwarf spheroidal galaxies (dSphs) using the phase-space distribution function (DF) method. After assessing the systematics of the approach against mock data from the Gaia Challenge project, we apply the DF analysis to the entire kinematic sample of well-measured MW dwarf satellites for the first time. Contrary to previous findings for some of these objects, we find that the DF analysis yields results consistent with the standard Jeans analysis. In particular, in this study we rediscover (i) a large diversity in the inner halo densities of dSphs (bracketed by Draco and Fornax), and (ii) an anticorrelation between inner halo density and pericenter distance of the bright MW satellites. Regardless of the strength of the anticorrelation, we find that the distribution of these satellites in density versus pericenter space is inconsistent with the results of the high-resolution N -body simulations that include a disc potential. Our analysis motivates further studies on the role of internal feedback and dark matter microphysics in these dSphs. [ABSTRACT FROM AUTHOR]

Two decades on, the study of hypervelocity stars is still in its infancy. These stars can provide novel constraints on the total mass of the Galaxy and its dark matter distribution. However how these stars are accelerated to such high velocities is unclear. Various proposed production mechanisms for these stars can be distinguished using chemo-dynamic tagging. The advent of Gaia and other large surveys have provided hundreds of candidate hyper velocity objects to target for ground-based high-resolution follow-up observations. We conduct high-resolution spectroscopic follow-up observations of 16 candidate late-type hyper velocity stars using the Apache Point Observatory and the McDonald Observatory. We derive atmospheric parameters and chemical abundances for these stars. We measure up to 22 elements, including the following nucleosynthetic families: |$\alpha$| (Mg, Si, Ca, and Ti), light/odd-Z (Na, Al, V, Cu, and Sc), Fe-peak (Fe, Cr, Mn, Co, Ni, and Zn), and neutron capture (Sr, Y, Zr, Ba, La, Nd, and Eu). Our kinematic analysis shows one candidate is unbound, two are marginally bound, and the remainder are bound to the Galaxy. Finally, for the three unbound or marginally bound stars, we perform orbit integration to locate possible globular cluster or dwarf galaxy progenitors. We do not find any likely candidate systems for these stars and conclude that the unbound stars are likely from the the stellar halo, in agreement with the chemical results. The remaining bound stars are all chemically consistent with the stellar halo as well. [ABSTRACT FROM AUTHOR]

The mass distribution in the Local Group (LG), dominated by the Andromeda (M31) and Milky Way (MW) pair, is highly anisotropic. We use the APOSTLE simulations to examine how this anisotropy manifests on the spatial distribution and kinematics of dwarf galaxies out to a distance of |$d_{\rm MW}\sim 3$|  Mpc from the MW. The simulations indicate a preference for dwarfs to be located near the axis defined by the MW-M31 direction, even for dwarfs in the LG periphery (LGP; i.e. at distances |$1.25\ \lt\ d_{\rm MW}/$| Mpc |$\lt\ 3$|⁠). The 'Hubble flow' in the periphery is also affected; at fixed |$d_{\rm MW}$| the mean recession speed, |$\langle V_{\rm rad} \rangle$|⁠ , varies with angular distance to M31, peaking in the anti-M31 direction and reaching a minimum behind M31. The M31-MW mass decelerates the local expansion; the LG 'turnaround radius' (i.e. where |$\langle V_{\rm rad} \rangle =0$|⁠) in APOSTLE is at |$r \sim 1.25$|  Mpc from the LG barycentre and the pure Hubble flow (where |$\langle V_{\rm rad} \rangle \sim H_0*d$|⁠) is reached beyond |$r\sim 3$|  Mpc. The predicted flow is very cold, with a barycentric dispersion of |$\lt 40$|  km s−1. Comparing these predictions with observations yields mixed results. There is little evidence for a preferred alignment of dwarfs along the MW-M31 direction, but some evidence for an angular anisotropy in |$\langle V_{\rm rad} \rangle$|⁠. Although the 'coldness' of the Hubble flow is consistent with the simulations, it is less decelerated: relative to the MW all galaxies beyond |$d_{\rm MW} \sim 1.25$|  Mpc seem to be already on a pure Hubble flow. We argue that these oddities may result at least partly from incompleteness and inhomogeneous sky coverage in our current inventory of nearby dwarfs. [ABSTRACT FROM AUTHOR]

We present an extended suite of the Auriga cosmological gravo-magnetohydrodynamical 'zoom-in' simulations of 40 Milky Way-mass haloes and 26 dwarf galaxy–mass haloes run with the moving-mesh code arepo. Auriga adopts the Lambda cold dark matter cosmogony and includes a comprehensive galaxy formation physics model following the coupled cosmic evolution of dark matter, gas, stars, and supermassive black holes which has been shown to produce numerically well-converged galaxy properties for Milky Way-mass systems. We describe the first public data release of this augmented suite of Auriga simulations, which includes raw snapshots, group catalogues, merger trees, initial conditions, and supplementary data, as well as public analysis tools with worked examples of how to use the data. To demonstrate the value and robustness of the simulation predictions, we analyse a series of low-redshift global properties that compare well with many observed scaling relations, such as the Tully–Fisher relation, the star-forming (SF) main sequence, and H  i gas fraction/disc thickness. Finally, we show that SF gas discs appear to build rotation and velocity dispersion rapidly for |$z\gtrsim 3$| before they 'settle' into ever-increasing rotation-dispersion ratios (⁠|$V/\sigma$|⁠). This evolution appears to be in rough agreement with some kinematic measurements from H |$\alpha$| observations, and demonstrates an application of how to utilize the released data. [ABSTRACT FROM AUTHOR]

We present the first study on the gravitational impact of supernova feedback in an isolated soliton and a spherically symmetric dwarf scalar field dark matter (SFDM) halo of virial mass |$1\times 10^{10}\,\mathrm{M_\odot }$|⁠. We use a boson mass |$m=10^{-22}\,\mathrm{eV\,c^{-2}}$| and a soliton core |$r_\mathrm{ c} \approx 0.7$| kpc, comparable to typical half-light radii of Local Group dwarf galaxies. We simulate the rapid gas removal from the centre of the soliton by a concentric external time-dependent Hernquist potential. We explore two scenarios of feedback blowouts: (i) a massive single burst and (ii) multiple consecutive blowouts injecting the same total energy to the system, including various magnitudes for the blowouts in both scenarios. In all cases, we find one single blowout has a stronger effect on reducing the soliton central density. Feedback leads to central soliton densities that oscillate quasi-periodically for an isolated soliton and stochastically for an SFDM halo. The range in the density amplitude depends on the strength of the blowout; however, we observe typical variations of a factor of |$\geqslant$| 2. One important consequence of the stochastic fluctuating densities is that, if we had no prior knowledge of the system evolution, we can only know the configuration profile at a specific time within some accuracy. By fitting soliton profiles at different times to our simulated structures, we found the (1 |$\sigma$|⁠) scatter of their time-dependent density profiles. For configurations within the 1 |$\sigma$| range, we find the inferred boson mass is typically less than 20 per cent different from the real value used in our simulations. Finally, we compare the observed dynamical masses of field dwarf galaxies in our Local Group with the implied range of viable solitons from our simulations and find good agreement. [ABSTRACT FROM AUTHOR]

We study the statistics of dwarf galaxy populations as a function of environment in cold dark matter (CDM) and warm dark matter (WDM; sterile neutrino model mass |$M_{{\rm s}}=7.1~{\rm keV}$|⁠ ; half-mode mass |$M_{{\rm hm}} = 6.3\times 10^8$|   |${\rm M}_\odot$|⁠ ; and thermal relic equivalent mass |$m_{{\rm th}} = 2.8~{\rm keV}$|⁠) cosmogonies, using the Evolution and Assembly of GaLaxies and their Environments (EAGLE) galaxy formation model in two counterpart simulations. We measure the abundance of dwarf galaxies within 3 Mpc of DM haloes with a present-day halo mass similar to the Milky Way, finding that the number of galaxies |$M_{*}\gt 10^7$|   |${\rm M}_\odot$|  is nearly identical for WDM and CDM. However, the cumulative mass function becomes shallower for WDM at lower masses, yielding 50 per cent fewer dwarf galaxies of |$M_{*}\gtrsim 10^{5}$|   |${\rm M}_\odot$|  than CDM. The suppression of low-mass halo counts in WDM increases significantly from high- to low-density regions for haloes in the |$[0.5,2] \times M_ {\rm hm}$| range. The fraction of haloes hosting resolvable galaxies (⁠|$M_*\gtrsim 10^{5}$|   |${\rm M}_\odot$|  ) also diverges from overdense to underdense regions for |$M\gt 2M_ {\rm hm}$|⁠ , as the increased collapse delay at small densities pushes the collapse to after the reionization threshold. However, the stellar mass of WDM haloes at |$[0.5,2]\times M_ {\rm hm}$| is 30 per cent higher per unit halo mass than CDM haloes in underdense regions. We conclude that the suppression of galaxies with |$M_{*}\gtrsim 10^5$|   |${\rm M}_\odot$|  between WDM and CDM is independent of density: the suppression of halo counts and fraction of luminous haloes is balanced by an enhancement in stellar mass–halo mass relation. [ABSTRACT FROM AUTHOR]

Our ability to trace the star-forming molecular gas is important to our understanding of the Universe. We can trace this gas using CO emission, converting the observed CO intensity into the H |$_2$| gas mass of the region using the CO-to-H |$_2$| conversion factor (⁠|$X_{\rm{{\small CO}}}$|⁠). In this paper, we use simulations to study the conversion factor and the molecular gas within galaxies. We analysed a suite of simulations of isolated disc galaxies, ranging from dwarfs to Milky Way-mass galaxies, that were run using the fire-2 subgrid models coupled to the chimes non-equilibrium chemistry solver. We use the non-equilibrium abundances from the simulations, and we also compare to results using abundances assuming equilibrium, which we calculate from the simulation in post-processing. Our non-equilibrium simulations are able to reproduce the relation between CO and H |$_2$| column densities, and the relation between |$X_{\rm{{\small CO}}}$| and metallicity, seen within observations of the Milky Way. We also compare to the xCOLD GASS survey, and find agreement with their data to our predicted CO luminosities at fixed star formation rate. We also find the multivariate function used by xCOLD GASS overpredicts the H |$_2$| mass for our simulations, motivating us to suggest an alternative multivariate function of our fitting, though we caution that this fitting is uncertain due to the limited range of galaxy conditions covered by our simulations. We also find that the non-equilibrium chemistry has little effect on the conversion factor (<5 per cent) for our high-mass galaxies, though still affects the H |$_2$| mass and |$L_{\rm{{\small CO}}}$| by |$\approx$| 25  per cent. [ABSTRACT FROM AUTHOR]

The chemical abundances of Milky Way's (MW's) satellites reflect their star formation histories (SFHs), yet, due to the difficulty of determining the ages of old stars, the SFHs of most satellites are poorly measured. Ongoing and upcoming surveys will obtain around 10 times more medium-resolution spectra for stars in satellites than are currently available. To correctly extract SFHs from large samples of chemical abundances, the relationship between chemical abundances and SFHs needs to be clarified. Here, we perform a high-resolution cosmological zoom-in simulation of a MW-like galaxy with detailed models of star formation, supernova (SN) feedback, and metal diffusion. We quantify SFHs, metallicity distribution functions, and the α -element (Mg, Ca, and Si) abundances in satellites of the host galaxy. We find that star formation in most simulated satellites is quenched before infalling to their host. Star formation episodes in simulated satellites are separated by a few hundred Myr owing to SN feedback; each star formation event produces groups of stars with similar [ α /Fe] and [Fe/H]. We then perform a mock observation of the upcoming Subaru Prime Focus Spectrograph (PFS) observations. We find that Subaru PFS will be able to detect distinct groups of stars in [ α /Fe] versus [Fe/H] space, produced by episodic star formation. This result means that episodic SFHs can be estimated from the chemical abundances of ≳1000 stars determined with medium-resolution spectroscopy. [ABSTRACT FROM AUTHOR]

The epoch of reionization (EoR) progressed through the emission of ionizing photons from galaxies to their local intergalactic medium. In this work, we characterize the dwarf star-forming galaxies as candidates for the source of ionizing photons that drove EoR. We investigate the ionizing properties and star formation histories of star-forming dwarf galaxies at the last stages of EoR at |$4.8\lt z \lt 7$| using observations from the CAnadian NIRISS Unbiased Cluster Survey (CANUCS). The magnification due to gravitational lensing allows us to probe large dynamic ranges in stellar mass (⁠|$2\times 10^{6}\le {M}_*/{\rm M}_\odot \le 5\times 10^{9}$|⁠) and ultraviolet (UV) magnitudes (⁠|$-22.68\le M_{\rm UV}\le =-15.95$|⁠). We find a median UV slope |$\beta _{1500}\,$| of |$-2. 56\pm 0.23$| and the production efficiency of ionizing photons |$\log$| |$\xi _{\rm {ion}}\,$| |$=25.39\pm 0.6$| for the full sample (⁠|$4.8\lt z \lt 7$|⁠) with a median stellar mass of |$6.3\pm 0.5\times 10^{7} \, {\rm M}_\odot$|⁠. We find both |$\beta _{1500}\,$| and |$\xi _{\rm {ion}}\,$| are marginally correlated with the stellar mass of the galaxy, indicating a possible greater contribution of dwarf galaxies to the reionization of the Universe. We find that on average, galaxies in our sample are experiencing a recent rise/burst of star formation which translates to a higher scatter in |$\xi _{\rm {ion}}\,$| and a large scatter in H |$\alpha$| equivalent widths (EWs). Finally, we investigate the trends of H |$\alpha$| and [O  iii ] + H |$\beta$| EWs with UV magnitude and find |$M_{\rm UV}$| is correlated between H |$\alpha$| but not with [O  iii ] + H |$\beta$| EWs indicating low metallicities and recent burst in the UV faint galaxies. [ABSTRACT FROM AUTHOR]

Active star formation in dwarf galaxies shapes the morphology of the surrounding nebular environment and ensures the non-uniformity of the chemical elements spatial distribution in it due to the superwind region expansion. Ionizing radiation within the nebular gas produces observed emission lines used for modelling and diagnostics. We introduce a multicomponent photoionization modelling (MPhM) approach that incorporates detailed calculation of diffuse ionizing radiation (DCDIR) based on chemodynamical simulations (ChDSs). Our models aim to replicate crucial emission line intensity ratios within the observed range, employing a thin dense shell between the superwind region and the outer nebular environment to address ChDSs resolution limitations, which render them insensitive to the presence of a superwind shock. MPhM-generated emission line spectra within a small central synthetic aperture and a thin long-slit exhibit excellent agreement with observations, confirming the accuracy of the ionization structure of the nebular environment obtained using the MPhM + DCDIR approach. However, the outward-only approximation fails to reproduce the dwarf galaxies ionization structure. We determined the oxygen abundance using the |$T_e$| - and |$R_{23}$| -methods based on emission lines from MPhM + DCDIR. The resulting abundances align well with values obtained by averaging over the 'observed' volume within synthetic apertures, weighted by mass. The escape fraction of ionizing photons from the dwarf galaxy was found to be larger than that obtained using the outward-only approximation. Employing Kennicutt's calibration corrected for near-UV data, the star formation rate (SFR) was calculated using the |${\rm H}\,\alpha$| luminosity from MPhM + DCDIR. The resulting SFR value is nearly 33 per cent higher than the true one. [ABSTRACT FROM AUTHOR]

The observationally inferred size versus stellar–mass relationship (SMR) for low-mass galaxies provides an important test for galaxy formation models. However, the relationship relies on assumptions that relate observed luminosity profiles to underlying stellar mass profiles. Here we use the Feedback in Realistic Environments simulations of low-mass galaxies to explore how the predicted SMR changes depending on whether one uses star-particle counts directly or mock observations. We reproduce the SMR found in The Exploration of Local Volume Satellites survey remarkably well only when we infer stellar masses and sizes using mock observations. However, when we use star particles to directly infer stellar masses and half-mass radii, we find that our galaxies are too large and obey an SMR with too little scatter compared to observations. This discrepancy between the 'true' galaxy size and mass and those derived in the mock observation approach is twofold. First, our simulated galaxies have higher and more varied mass-to-light ratios (MLR) at a fixed colour than those commonly adopted, which tends to underestimate their stellar masses compared to their true, simulated values. Second, our galaxies have radially increasing MLR gradients therefore using a single MLR tends to underpredict the mass in the outer regions. Similarly, the true half-mass radius is larger than the half-light radius because the light is more concentrated than the mass. If our simulations are accurate representations of the real Universe, then the relationship between galaxy size and stellar mass is even tighter for low-mass galaxies than is commonly inferred from observed relations. [ABSTRACT FROM AUTHOR]

Given their dominance of the galaxy number density, dwarf galaxies are central to our understanding of galaxy formation. While the incidence of active galactic nuclei (AGN) and their impact on galaxy evolution have been extensively studied in massive galaxies, much less is known about the role of AGN in the evolution of dwarfs. We search for radiatively efficient AGN in the nearby (0.1 < z < 0.3) dwarf (108 M⊙ < M ⋆ < 1010 M⊙) population, using spectral energy distribution fitting (via prospector) applied to deep ultraviolet to mid-infrared photometry of 508 dwarf galaxies. Around a third (32 ± 2 per cent) of our dwarfs show signs of AGN activity. We compare the properties of our dwarf AGN to control samples, constructed from non-AGN, which have the same distributions of redshift and stellar mass as their AGN counterparts. Kolmogorov–Smirnov tests between the AGN and control distributions indicate that the AGN do not show differences in their distances to nodes, filaments, and nearby massive galaxies from their control counterparts. This indicates that AGN triggering in the dwarf regime is not strongly correlated with local environment. The fraction of AGN hosts with early-type morphology and those that are interacting are also indistinguishable from the controls within the uncertainties, suggesting that interactions do not play a significant role in inducing AGN activity in our sample. Finally, the star formation activity in dwarf AGN is only slightly lower than that in their control counterparts, suggesting that the presence of radiatively efficient AGN does not lead to significant, prompt quenching of star formation in these systems. [ABSTRACT FROM AUTHOR]

We analyze four epochs of Hubble Space Telescope imaging over 18 yr for the Draco dwarf spheroidal galaxy. We measure precise proper motions for hundreds of stars and combine these with existing line-of-sight (LOS) velocities. This provides the first radially resolved 3D velocity dispersion profiles for any dwarf galaxy. These constrain the intrinsic velocity anisotropy and resolve the mass–anisotropy degeneracy. We solve the Jeans equations in oblate axisymmetric geometry to infer the mass profile. We find the velocity dispersion to be radially anisotropic along the symmetry axis and tangentially anisotropic in the equatorial plane, with a globally averaged value β B ¯ = − 0.20 − 0.53 + 0.28 , (where 1 – β B ≡ 〈 v tan 2 〉 / 〈 v rad 2 〉 in 3D). The logarithmic dark matter (DM) density slope over the observed radial range, Γdark, is − 0.83 − 0.37 + 0.32 , consistent with the inner cusp predicted in ΛCDM cosmology. As expected given Draco's low mass and ancient star formation history, it does not appear to have been dissolved by baryonic processes. We rule out cores larger than 487, 717, and 942 pc at 1 σ, 2 σ, and 3 σ confidence, respectively, thus imposing important constraints on the self-interacting DM cross section. Spherical models yield biased estimates for both the velocity anisotropy and the inferred slope. The circular velocity at our outermost data point (900 pc) is 24.19 − 2.97 + 6.31 km s − 1 . We infer a dynamical distance of 75.37 − 4.00 + 4.73 kpc and show that Draco has a modest LOS rotation, with v / σ = 0.22 ± 0.09 . Our results provide a new stringent test of the so-called "cusp–core" problem that can be readily extended to other dwarfs. [ABSTRACT FROM AUTHOR]

Nearby dwarf galaxies display a variety of effective radii (sizes) at a given stellar mass, suggesting different evolution scenarios according to their final "stellar" size. The TNG hydrodynamical simulations present a bimodality in the z = 0 size–mass relation (SMRz0) of dwarf galaxies, at r1/2, ⋆ ∼ 450 pc. Using the TNG50 simulation, we explored the evolution of the most massive progenitors of dwarf galaxies (z = 0 log(M⋆/M⊙) between 8.4 and 9.2) that end up as central galaxies of their groups. We split these dwarfs into three classes of the SMRz0: "Normals" from the central spine of the main branch, and "Compacts" from the secondary branch as well as the lower envelope of the main branch. Both classes of Compacts see their stellar sizes decrease from z ∼ 1 onwards in contrast to Normals, while the sizes of the gas and dark matter (DM) components continue to increase (as for Normals). A detailed analysis reveals that Compacts live in poorer environments, and thus suffer fewer major mergers from z = 0.8 onwards, which otherwise would pump angular momentum into the gas, allowing strong gas inflows, producing inner star formation, and thus leading to the buildup of a stellar core. Compacts are predicted to be rounder and to have bluer cores. Compact dwarfs of similar sizes are observed in the GAMA survey, but the bimodality in size is less evident and the most compact dwarfs tend to be passive rather than star forming, as in TNG50. Our conclusions should therefore be confirmed with future cosmological hydrodynamical simulations. [ABSTRACT FROM AUTHOR]

The Sagittarius dwarf spheroidal (Sgr dSph) galaxy provides one of the most convincing examples of tidal interaction between satellite galaxies and the Milky Way (MW). The main body of the dwarf was recently demonstrated to have an elongated, prolate, bar-like shape and to possess some internal rotation. Whether these features are temporary results of the strong tidal interaction at the recent pericenter passage or are due to a disky progenitor is a matter of debate. I present an analog of Sgr selected among bar-like galaxies from the TNG50 simulation of the IllustrisTNG project. The simulated dwarf is initially a disky galaxy with mass exceeding 1011 M⊙ and evolves around a MW-like host on a tight orbit with seven pericenter passages and a period of about 1 Gyr. At the second pericenter passage, the disk transforms into a bar and the bar-like shape of the stellar component is preserved until the end of the evolution. The morphological transformation is accompanied by strong mass loss, leaving a dwarf with a final mass of below 109 M⊙. The gas is lost completely and the star formation ceases at the third pericenter passage. At the last pericenters, the dwarf possesses a bar-like shape, a little remnant rotation, and the metallicity gradient, which are consistent with observations. The more concentrated metal-rich stellar population rotates faster and has a lower velocity dispersion than the more extended metal-poor one. The metallicity distribution evolves so that the most metal-poor stars are stripped first, which explains the metallicity gradient detected in the Sgr stream. This study demonstrates that a dSph galaxy with properties akin to the Sgr dwarf can form from a disky progenitor with a mass of above 1011 M⊙ by tidal evolution around the MW in the cosmological context. [ABSTRACT FROM AUTHOR]

Context. Recent observations of galaxy mergers inside galaxy cluster environments, such as NGC 5291 in the vicinity of Abell 3574, report high star formation rates in the ejected tidal tails, which point towards currently developing tidal dwarf galaxies. This prompts the intriguing question whether these newly formed stellar structures could get stripped from the galaxy potential by the cluster and thus populate it with dwarf galaxies. Aims. We verify whether environmental stripping of tidal dwarf galaxies from galaxy mergers inside galaxy cluster environments is a possible evolutionary channel to populate a galaxy cluster with low-mass and low surface brightness galaxies. Methods. We performed three high-resolution hydrodynamical simulations of mergers between spiral galaxies in a cluster environment, implementing a stellar mass ratio of 2:1 with M200 = 9.5 × 1011 M⊙ for the more massive galaxy. Between the three different simulations, we varied the initial orbit of the infalling galaxies with respect to the cluster center. Results. We demonstrate that cluster environments are capable of stripping tidal dwarf galaxies from the host potential independently of the infall orbit of the merging galaxy pair, without instantly destroying the tidal dwarfs. Starting to evolve separately from their progenitor, these newly formed dwarf galaxies reach total masses of Mtot ≈ 107 − 9 M⊙ within the limits of our resolution. In the three tested orbit scenarios, we find three, seven, and eight tidal dwarf galaxies per merger, respectively, which survive longer than 1 Gyr after the merger event. Exposed to ram pressure, these gas dominated dwarf galaxies exhibit high star formation rates while also losing gas to the environment. Experiencing a strong headwind due to their motion through the intracluster medium, they quickly lose momentum and start spiraling towards the cluster center, reaching distances on the order of 1 Mpc from their progenitor. About 4 Gyr after the merger event, we still find three and four intact dwarf galaxies in two of the tested scenarios, respectively. The other stripped tidal dwarf galaxies either evaporate in the hostile cluster environment due to their low initial mass, or are disrupted as soon as they reach the cluster center. Conclusions. The dwarf production rate due to galaxy mergers is elevated when the interaction with a cluster environment is taken into account. Comparing their contribution to the observed galaxy mass function in clusters, our results indicate that ∼30% of dwarf galaxies in clusters could have been formed by stripping from galaxy mergers. [ABSTRACT FROM AUTHOR]

Aims. Green peas (GPs) are young, compact, star-forming dwarf galaxies, and local (z ∼ 0.3) analogues of the early galaxies (z ≥ 6) considered to be mainly responsible for the reionisation of the Universe. Recent X-ray observations of GPs led to the detection of high excess emission, which cannot be accounted for by star formation alone and implies the presence of an active galactic nucleus (AGN). We employ radio observations to study the radio properties of GPs, build their radio spectral energy distributions, and verify the presence of AGNs. Methods. We performed new radio observations of three GPs with the Karl G. Jansky Very Large Array (JVLA) in the L, C, and X bands (1.4, 6 and 10 GHz resp.), and analysed them alongside data from archival observations and large radio surveys. We also analysed the archival radio data for a larger sample of GPs and blueberry (BBs) galaxies, which are lower-mass and lower-redshift analogues of the GPs. To understand the significance of the radio observations, we assess the detectability of these sources, and compare the detected radio luminosities with expectations from theoretical and empirical relations. Results. Two of the three targeted GPs are strongly detected (> 10σ) in the JVLA observations and their fluxes are consistent with star formation, while the third source is undetected. Although archival radio surveys have the sensitivity to detect a large fraction (∼75%) of the sources from the larger archival sample of GPs and BBs, we only detect a small number (< 40%) of them and their radio luminosity is significantly lower than the expectation from empirical relations. Conclusions. Our results show that the majority of the dwarf galaxies in our sample are highly underluminous. The radio luminosity–star formation rate (SFR) relation deviates from the empirical relations, especially towards the lower end of galaxy mass and SFR, suggesting that the relations established for larger galaxies may not hold towards the low-mass end. [ABSTRACT FROM AUTHOR]

Context. The Small Magellanic Cloud (SMC) is an ideal laboratory for studying the properties of star-forming regions thanks to its low metallicity, which has an impact on the molecular gas abundance. However, a small number of molecular gas surveys of the entire galaxy have been carried out in the last few years, limiting the measurements of interstellar medium (ISM) properties in a homogeneous manner. Aims. We present the CO(3-2) APEX survey at a 6 pc resolution of the bar of the SMC, observed with the SuperCAM receiver attached to the APEX telescope. This high-resolution survey has allowed us to study certain properties of the ISM and to identify CO clouds in the innermost parts of the H2 envelopes. Methods. We adopted the CO analysis in the SMC bar comparing the CO(3–2) survey with that of the CO(2–1) of a similar resolution. We studied the CO(3–2)-to-CO(2–1) ratio (R32), which is very sensitive to the environment properties (e.g., star-forming regions). We analyzed the correlation of this ratio with observational quantities that trace the star formation such as the local CO emission, the Spitzer color [70/160], and the total IR surface brightness measured from the Spitzer and Herschel bands. For the identification of the CO(3–2) clouds, we used the CPROPS algorithm, which allowed us to measure the physical properties of the clouds. We analyzed the scaling relationships of such physical properties. Results. We obtained R32 = 0.65 ± 0.02 for the SW bar and a slightly higher ratio, R32 = 0.7 ± 0.1, for N66 in the SMC. We found that R32 varies from region to region, depending on the star formation activity. In regions dominated by HII and photo-dissociated regions (e.g., N22, N66) R32 tends to be higher than the median values. Meanwhile, lower values were found toward quiescent clouds. We also found that R32 is correlated with the IR color [70/160] and the total IR surface brightness. This finding indicates that R32 increases with environmental properties, such as the dust temperature, total gas density, and radiation field. We identified 225 molecular clouds with sizes of R > 1.5 pc and signal-to-noise ratios (S/N) of >3, of which only 17 are well resolved CO(3–2) clouds with S/N ≳ 5. These 17 clouds follow consistent scaling relationships to the inner Milky Way clouds but with some departures. For instance, CO(3–2) tends to be less turbulent and less luminous than the inner Milky Way clouds of similar sizes. Finally, we estimated a median virial-based CO(3–2)-to-H2 conversion factor of 12.6−7+10M⊙ (K km s−1 pc2)−1 for the total sample. [ABSTRACT FROM AUTHOR]

Context. The number of known globular clusters in the Galactic bulge has been increasing steadily thanks to different new surveys. Aims. The aim of this study is to provide a census of the newly revealed globular clusters in the Galactic bulge, and analyze their characteristics. Methods. In recent years, many globular clusters have been discovered or identified. The stellar populations to which they belong are indicated in their original studies: they are mostly bulge clusters, with some identified as disk or halo members. We collected 41 new globular clusters revealed in the last decade and compared them to the known bulge clusters. Results. The new clusters are intrinsically faint with MV of around −6.0 mag. The distance to the Sun of the ensemble of well-known and new bulge clusters is compatible with the Galactocentric distance measurements from the Galactic black hole location. The ensemble sample shows metallicity peaks at [Fe/H] ∼ −1.08 ± 0.35 and −0.51 ± 0.25 dex, confirming previous findings. The age–metallicity relation of the new clusters younger than 10 Gyr is compatible with that of the ex situ samples of the dwarf galaxies Sagittarius, Canis Majoris, and Gaia-Enceladus-Sausage. The clusters with ages between 11.5 and 13.5 Gyr show no age–metallicity relation, because they are all old. This is compatible with their formation in situ in the early Galaxy. [ABSTRACT FROM AUTHOR]

The Dark Energy Spectroscopic Instrument Milky Way Survey (DESI MWS) will explore the assembly history of the Milky Way by characterizing remnants of ancient dwarf galaxy accretion events and improving constraints on the distribution of dark matter in the outer halo. We present mock catalogues that reproduce the selection criteria of MWS and the format of the final MWS data set. These catalogues can be used to test methods for quantifying the properties of stellar halo substructure and reconstructing the Milky Way's accretion history with the MWS data, including the effects of halo-to-halo variance. The mock catalogues are based on a phase-space kernel expansion technique applied to star particles in the Auriga suite of six high-resolution lambda-cold dark matter magnetohydrodynamic zoom-in simulations. They include photometric properties (and associated errors) used in DESI target selection and the outputs of the MWS spectral analysis pipeline (radial velocity, metallicity, surface gravity, and temperature). They also include information from the underlying simulation, such as the total gravitational potential and information on the progenitors of accreted halo stars. We discuss how the subset of halo stars observable by MWS in these simulations corresponds to their true content and properties. These mock Milky Ways have rich accretion histories, resulting in a large number of substructures that span the whole stellar halo out to large distances and have substantial overlap in the space of orbital energy and angular momentum. [ABSTRACT FROM AUTHOR]

This paper investigates a mathematical model of a star formation system, including in-fall of gas from the local environment and out-flow of gas due to supernovae explosions and perturbations. In particular, the objective is to study how the variable density of interstellar components of the system namely atomic, molecular, and stellar components, interact in the star formation cycle. Under special parametric conditions, both limit cycle and stationary state behavior are observed. This indicates a stable star formation cycle in discrete episodes and an unstable star formation cycle converging to a stationary state. Observations of duty cycles under various parameters with varying intensity of supernovae shockwaves for dwarf galaxies, showed that the system adopts a self-regulatory oscillation state beyond a particular value. Analysis of giant galaxies showed decreased oscillatory periods for higher values. This is implied by the low production rate of supernovae in dwarf galaxies, increased production of cold gas, continuation of the cyclic behavior for a longer time. Stronger shockwaves increase the rate of dissipation of gases, resulting in shredding of mass, to get transferred into a precipitous lower mass. Star-forming rate (SFR) of high-mass star systems was found to vary against higher-order perturbations of supernovae shockwave but remained the same in the case of low-mass star systems. [ABSTRACT FROM AUTHOR]

Henize 2–10 is a dwarf galaxy experiencing positive black hole (BH) feedback from a radio-detected low-luminosity active galactic nucleus. Previous Green Bank Telescope (GBT) observations detected a H2O "kilomaser" in Henize 2–10, but the low angular resolution (33″) left the location and origin of the maser ambiguous. We present new Karl G. Jansky Very Large Array observations of the H2O maser line at 22.23508 GHz in Henize 2–10 with ∼2″ resolution. These observations reveal two maser sources distinct in position and velocity. The first maser source is spatially coincident with the known BH outflow and the region of triggered star formation ∼70 pc to the east. Combined with the broad width of the maser (W 50 ∼ 66 km s−1), this confirms our hypothesis that part of the maser detected with the GBT is produced by the impact of the BH outflow shocking the dense molecular gas along the flow and at the interface of the eastern star-forming region. The second maser source lies to the southeast, far from the central BH, and has a narrow width (W 50 ∼ 8 km s−1), suggesting a star formation–related origin. This work has revealed the nature of the H2O kilomaser in Henize 2–10 and illustrates the first known connection between outflow-driven H2O masers and positive BH feedback. [ABSTRACT FROM AUTHOR]

This is the second paper in a series, which studies the likelihood that some globular clusters (GCs) of the Milky Way (MW) could have originated from a dwarf satellite galaxy (DSG). Using a large suite of three-body simulations we determine the present-day orbital properties of 154 GCs that could have escaped from 41 MW DSGs over the past |$8\ \mathrm{Gyr}$|⁠. For the MW we considered two sets of static and dynamic models which account for the sustained growth of the MW since its birth. We focus on the Magellanic clouds and Sagittarius. We compare the apogalactic distance, eccentricity, and orbital inclination of the MW GCs with those of runaway GCs from DSGs, to constrain their possible ex-situ origin. We observe a positive correlation between a DSG mass and the dispersion of its runaway GCs in the orbital parameter space of (R ap, e). We provide tables of the identified MW GCs and their likely associated progenitors. In total, we find 29 (19 per cent) MW GCs which could be kinematically associated with MW DSGs. We report, for the first time, 6 and 10 new associations with the Large Magellanic Cloud and the Sagittarius, respectively. For the Sagittarius we predict a concentration of runaway GCs at large apogalactic distances of |$R_\mathrm{ap}\approx 275-375 \ \mathrm{kpc}$|⁠ , e ≈ 0.8, and a relative inclination of Δθ ≈ 20°. So far, there has not been any observed GCs with such orbital elements. Complemented with photometric and spectroscopic observations, and cosmological simulations, the findings from the present study could conclusively settle the debate over the in-situ versus ex-situ origin of the MW GCs. [ABSTRACT FROM AUTHOR]

Recent studies on dwarf galaxies reveal that some of them harbour a massive black hole (BH), which is believed to have a similar mass of the supermassive BH 'seeds' at early times. The origin and growth of the primitive BHs are still open questions, since these BH seeds are hardly observed at high redshifts. Therefore, MBH of dwarf galaxies can be the perfect candidates to untangle BH 'seeds' properties and their influence on their host galaxy evolution, since MBH may preserve their initial conditions due to its quiet merger and accretion histories. We use optical integral field unit observations, obtained with the Gemini GMOS-IFU, to study the gas emission and kinematics in four dwarf galaxies, candidates to host MBH, based on the analysis of their [Fe  x ] luminosities measured from SDSS spectra. The [Fe  x ] emission line is not detected in our GMOS in any of the galaxies, prompting speculation that its absence in our recent data may stem from a past tidal disruption event coinciding with the observation period of the SDSS data. All galaxies exhibit extended gas emissions, and the spatially resolved emission-line ratio diagnostic diagrams present values that suggest active galactic nuclei (AGN) photoionization from the [S  ii ]–BPT diagram. The gas velocity fields of all galaxies are indicative of disturbed rotation patterns, with no detection of gas outflows in any of the sources. Although the [S  ii ]–BPT diagrams indicate AGN photoionization, further confirmation through multiwavelength observations is required to validate this scenario. [ABSTRACT FROM AUTHOR]

We present spatially resolved Keck Cosmic Web Imager stellar spectroscopy of the Virgo cluster dwarf galaxies VCC 9 and VCC 1448. These galaxies have similar stellar masses and large half-light radii but very different globular cluster (GC) system richness (∼25 versus ∼99 GCs). Using the KCWI data, we spectroscopically confirm 10 GCs associated with VCC 1448 and one GC associated with VCC 9. We make two measurements of dynamical mass for VCC 1448 based on the stellar and GC velocities, respectively. VCC 1448's mass measurements suggest that it resides in a halo in better agreement with the expectation of the stellar mass–halo mass relationship than the expectation from its large GC counts. For VCC 9, the dynamical mass we measure agrees with the expected halo mass from both relationships. We compare VCC 1448 and VCC 9 to the GC-rich galaxy Dragonfly 44 (∼74 GCs), which is similar in size but has ∼1 dex less stellar mass than either Virgo galaxy. In dynamical mass – GC number space, Dragonfly 44 and VCC 1448 exhibit richer GC systems given their dynamical mass than that of VCC 9 and other 'normal' galaxies. We also place the galaxies in kinematics–ellipticity space finding evidence of an anticorrelation between rotational support and the fraction of a galaxy's stellar mass in its GC system, that is, VCC 9 is more rotationally supported than VCC 1448, which is more rotationally supported than Dragonfly 44. This trend may be expected if a galaxy's GC content depends on its natal gas properties at formation. [ABSTRACT FROM AUTHOR]

We report on a |$\rm {[CII]}_{158\mu \rm {m}}$| search using the Atacama Large Millimeter/submillimeter Array (ALMA) on three lensed, confirmed Ly α emitting galaxies at z ∼ 7. Our targets are ultraviolet (UV) faint systems with stellar masses on the order of M * ∼ 109 M⊙. We detect a single [C  ii ] line emission (4σ) from the brightest (L ∼ 2.4 × 1010 L ⊙) galaxy in our sample, MACS0454-1251. We determine a systemic redshift (z [C  ii ] = 6.3151 ± 0.0005) for MACS0454-1251 and measure a Ly α velocity offset of |$\Delta v \approx 300 \pm 70 \rm {km\, s}^{-1}$|⁠. The remaining two galaxies we detect no [C  ii ] but provide 3σ upper limits on their [C  ii ] line luminosities which we use to investigate the |$L_{\textrm {[CII]}} - \rm {SFR}$| relation. Overall our single [C  ii ] detection shows agreement with the relation for local dwarf galaxies. Our [C  ii ] deficient galaxies could potentially be exhibiting low metallicities (Z < Z⊙). Another possible explanation for weaker [C  ii ] emission could be strong feedback from star formation disrupting molecular clouds. We do not detect continuum emission in any of the sources, placing upper limits on their dust masses. Assuming a single dust temperature of |$T_{d}=35 \rm {K}$| dust masses (M dust) range from <4.8 × 107 M⊙ to 2.3 × 108 M⊙. Collectively, our results suggest faint reionization era sources could be metal poor and/or could have strong feedback suppressing [C  ii ] emission. [ABSTRACT FROM AUTHOR]

NGC 6822 is a nearby (∼490 kpc) non-interacting low-metallicity (0.2 Z ⊙) dwarf galaxy which hosts several prominent H  ii regions, including sites of highly embedded active star formation. In this work, we present an imaging survey of NGC 6822 conducted with the Near Infrared Camera (NIRCam) and Mid-Infrared Instrument (MIRI) onboard JWST. We describe the data reduction, source extraction, and stellar population identifications from combined near- and mid-infrared (IR) photometry. Our NIRCam observations reach 7 mag deeper than previous JHKs surveys of this galaxy, which were sensitive to just below the tip of the red giant branch (TRGB). These JWST observations thus reveal for the first time in the near-IR the red clump stellar population and extend nearly 3 mag deeper. In the mid-IR, we observe roughly 2 mag below the TRGB with the MIRI F 770 W and F 1000 W filters. With these improvements in sensitivity, we produce a catalogue of ∼900 000 point sources over an area of ∼6.0 × 4.3 arcmin2. We present several NIRCam and MIRI colour–magnitude diagrams and discuss which colour combinations provide useful separations of various stellar populations to aid in future JWST observation planning. Finally, we find populations of carbon- and oxygen-rich asymptotic giant branch stars which will assist in improving our understanding of dust production in low-metallicity, early Universe analogue galaxies. [ABSTRACT FROM AUTHOR]

We present Hubble Space Telescope Advanced Camera for Surveys photometry of an arc structure of stars in the southern halo of M82. The structure is located at a projected height of ≈5 kpc from the disc of M82 but its stellar content exhibits a younger mean age than that of typical halo stars. We measured the distance, mean age, and peak metallicity of the stars in the arc and used them to determine the structure's origin. The arc colour–magnitude diagram yields a tip of the red giant branch (RGB) distance of 3.63 ± 0.08 Mpc, similar to that of M82, confirming its association with the galaxy. The colour–magnitude diagram also reveals a population of predominantly young stars with a mean age of ≈100–160 Myr, which is similar to that of the young stars formed in the tidal debris between M81, M82, and NGC 3077. We derived the mean metallicity of the halo stars surrounding the arc to be [Fe/H] ≈ −1.0, similar to that of the RGB population of the halo of M81. The RGB stars in the arc, while they are slightly more metal-rich than the halo RGB, show no spatial correlation with the young stars, suggesting that the arc is consists of mainly young stellar population. Furthermore, the observed age gradient along the structure of the arc indicates that the arc began forming from the closer side to M82, then moving outward. Taken together, the results suggest that the formation of the young stars that give rise to the arc structure could have been triggered by the interactions between M82's southern outflow and the H  i gas clouds surrounding it, representing a snapshot of a tidal dwarf galaxy in the process of forming. [ABSTRACT FROM AUTHOR]

Transient surveys routinely detect supernovae (SNe) without obvious host galaxies. To understand the demographics of these 'hostless' SNe and to constrain the possible host properties, we identify 161 SNe reported to the Transient Name Server since 2016 that do not have hosts catalogued from pre-explosion wide-field galaxy surveys. Using forced aperture photometry, we detect excess flux around only 56 of these SNe. Both thermonuclear and core-collapse (CC) SNe are present in our sample. Compared to flux-limited SNe samples with known hosts, superluminous supernovae (SLSNe), particularly hydrogen-deficient SLSNe, are over-represented here relative to all other SNe types; among CC SNe, there is also a higher fraction of interacting SNe than non-interacting. On the low-luminosity side, seven SNe have host absolute magnitude upper limits fainter than Mg  = −12, about 1 per cent of the Small Magellanic Cloud's luminosity; the faintest limits are close to the luminosity of globular clusters or ultra-faint dwarf galaxies (Mg ≃ −8). Fitting multiband forced photometry, 11 SNe have host stellar masses <106 M⊙ assuming quiescent hosts, and 13 SNe have host stellar masses <105 M⊙ assuming star-forming hosts. The spatial distribution of hostless SNe indicates that the majority are not associated with known galaxy groups and clusters, ruling out intracluster stellar light as the primary contributor of such SNe. Hostless Type Ia SNe tend to be more luminous and slow-fading than SNe Ia with known host galaxies, implying a hidden population of low-mass and star-forming hosts. We conclude that any undetected host galaxies are likely star-forming dwarfs in the field. [ABSTRACT FROM AUTHOR]

The Merian survey is mapping ∼ 850 deg2 of the Hyper Suprime-Cam Strategic Survey Program (HSC-SSP) wide layer with two medium-band filters on the 4-m Victor M. Blanco telescope at the Cerro Tololo Inter-American Observatory, with the goal of carrying the first high signal-to-noise (S/N) measurements of weak gravitational lensing around dwarf galaxies. This paper presents the design of the Merian filter set: N708 (λ c  = 7080 Å, Δλ = 275 Å) and N540 (λ c  = 5400 Å, Δλ = 210 Å). The central wavelengths and filter widths of N708 and N540 were designed to detect the |$\rm H\alpha$| and |$\rm [OIII]$| emission lines of galaxies in the mass range |$8\lt \rm \log M_*/M_\odot \lt 9$| by comparing Merian fluxes with HSC broad-band fluxes. Our filter design takes into account the weak lensing S/N and photometric redshift performance. Our simulations predict that Merian will yield a sample of ∼ 85 000 star-forming dwarf galaxies with a photometric redshift accuracy of σΔ z /(1 + z) ∼ 0.01 and an outlier fraction of |$\eta =2.8~{{\ \rm per\ cent}}$| over the redshift range 0.058 < z < 0.10. With 60 full nights on the Blanco/Dark Energy Camera (DECam), the Merian survey is predicted to measure the average weak lensing profile around dwarf galaxies with lensing S/N ∼32 within r < 0.5 Mpc and lensing S/N ∼90 within r < 1.0 Mpc. This unprecedented sample of star-forming dwarf galaxies will allow for studies of the interplay between dark matter and stellar feedback and their roles in the evolution of dwarf galaxies. [ABSTRACT FROM AUTHOR]

We present a detailed chemical abundance and kinematic analysis of six extremely metal-poor (−4.2 ≤ [Fe/H] ≤−2.9) halo stars with very low neutron-capture abundances ([Sr/H] and [Ba/H]) based on high-resolution Magellan/MIKE spectra. Three of our stars have [Sr/Ba] and [Sr/H] ratios that resemble those of metal-poor stars in ultra-faint dwarf galaxies (UFDs). Since early UFDs may be the building blocks of the Milky Way, extremely metal-poor halo stars with low, UFD-like Sr and Ba abundances may thus be ancient stars from the earliest small galactic systems that were accreted by the proto-Milky Way. We label these objects as Small Accreted Stellar System (SASS) stars, and we find an additional 61 similar ones in the literature. A kinematic analysis of our sample and literature stars reveals them to be fast-moving halo objects, all with retrograde motion, indicating an accretion origin. Because SASS stars are much brighter than typical UFD stars, identifying them offers promising ways towards detailed studies of early star formation environments. From the chemical abundances of SASS stars, it appears that the earliest accreted systems were likely enriched by a few supernovae whose light element yields varied from system to system. Neutron-capture elements were sparsely produced and/or diluted, with r -process nucleosynthesis playing a role. These insights offer a glimpse into the early formation of the Galaxy. Using neutron-capture elements as a distinguishing criterion for early formation, we have access to a unique metal-poor population that consists of the oldest stars in the universe. [ABSTRACT FROM AUTHOR]

We report the discovery of 23 globular cluster (GC) candidates around the relatively isolated dwarf galaxy IC 2574 within the Messier 81 (M81) group, at a distance of 3.86 Mpc. We use observations from the HST Advanced Camera for Surveys (ACS) to analyse the imaging in the F814W and F555W broad-band filters. Our GC candidates have luminosities ranging from −5.9 ≥ MV ≥ −10.4 and half-light radii of 1.4 ≤ r h ≤ 11.5 pc. We find the total number of GCs (N GC) = 27 ± 5 after applying completeness corrections, which implies a specific frequency of S N = 4.0 ± 0.8, consistent with expectations based on its luminosity. The GC system appears to have a bimodal colour distribution, with 30 percent of the GC candidates having redder colours. We also find five objects with extremely blue colours that could be young star clusters linked to an intense star formation episode that occurred in IC 2574 ∼1 Gyr ago. We make an independent measurement of the halo mass of IC 2574 from its kinematic data, which is rare for low mass galaxies, and find log M 200 = 10.93 ± 0.08. We place the galaxy on the well-known GC system mass–halo mass relation and find that it agrees well with the observed near-linear relation. IC 2574 has a rich GC population for a dwarf galaxy, which includes an unusually bright ω Cen-like GC, making it an exciting nearby laboratory for probing the peculiar efficiency of forming massive GCs in dwarf galaxies. [ABSTRACT FROM AUTHOR]

We present an atlas and follow-up spectroscopic observations of 87 thin stream-like structures detected with the STREAMFINDER algorithm in Gaia DR3, of which 28 are new discoveries. Here, we focus on using these streams to refine mass models of the Galaxy. Fits with a double-power-law halo with the outer power-law slope set to − β h = −3 yield an inner power-law slope of − γ h = - (0.97 − 0.21 + 0.17 ) , a scale radius of r 0 , h = 14.7 − 1.0 + 4.7 kpc , a halo density flattening q m, h = 0.75 ± 0.03, and a local dark matter density of ρ h,⊙ = 0.0114 ± 0.0007 M ⊙ pc−3. Freeing β yields β = 2.53 − 0.16 + 0.42 , but this value is heavily influenced by our chosen virial mass limit. The stellar disks are found to have a combined mass of 4.20 − 0.53 + 0.44 × 10 10 M ⊙ , with the thick disk contributing 12.4% ± 0.7% to the local stellar surface density. The scale lengths of the thin and thick disks are 2.17 − 0.08 + 0.18 and 1.62 − 0.13 + 0.72 kpc , respectively, while their scale heights are 0.347 − 0.010 + 0.007 and 0.86 − 0.02 + 0.03 kpc , respectively. The virial mass of the favored model is M 200 = 1.09 − 0.14 + 0.19 × 10 12 M ⊙ , while the mass inside of 50 kpc is M R <50 = 0.46 ± 0.03 × 1012 M ⊙. We introduce the Large Magellanic Cloud (LMC) into the derived potential models, and fit the Orphan stream therein, finding a mass for the LMC that is consistent with recent estimates. Some salient highlights include the nearby trailing arm of ω Cen, and a nearby very metal-poor stream that was once a satellite of the Sagittarius dwarf galaxy. Finally, we unambiguously detect a hot component around the GD-1 stream, consistent with it having been tidally preprocessed within its own dark matter subhalo. [ABSTRACT FROM AUTHOR]

We survey the young star cluster population in the dwarf galaxy NGC 4449 with the goal of investigating how stellar feedback may depend on the clusters' properties. Using ultraviolet (UV)–optical–near-infrared photometry obtained with the Hubble Space Telescope, we have recovered 99 compact sources exhibiting emission in the Pa β hydrogen recombination line. Our analysis reveals these sources possess masses of 102 < M ⊙ < 105, ages of 1–20 Myr, and a color excess E (B − V) in the range 0–1.4. After selecting clusters with masses above 3000 M ⊙ to mitigate stochastic sampling of the stellar initial mass function, we find that our IR-selected clusters have a median mass ∼ 7 × 103 M ⊙ and remain embedded in their surrounding gas and dust for 5–6 Myr. In contrast, line-emitting sources selected from existing UV/optical catalogs have a median mass ∼ 3.5 × 104 M ⊙ and have cleared their surroundings by 4 Myr. We further find that the environment in NGC 4449 has too low pressure to drive these differences. We interpret these findings as evidence that the clearing timescale from presupernova and supernova feedback is cluster mass dependent. Even in clusters with masses ∼ 7000 M ⊙, stochastic sampling of the upper end of the stellar initial mass function is present, randomly decreasing the number of massive stars available to inject energy and momentum into the surrounding medium. This effect may increase the clearing timescales in these clusters by decreasing the effectiveness of both presupernova and supernova feedback; neither models nor observations have so far explored such dependence explicitly. Future studies and observations with, e.g., the JWST, will fill this gap. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In this work, we investigate the discovery potential of low-mass Galactic dark matter (DM) subhaloes for indirect searches of DM. We use data from the Via Lactea II (VL-II) N -body cosmological simulation, which resolves subhaloes down to |$\mathcal {O}(10^4)$| solar masses and it is thus ideal for this purpose. First, we characterize the abundance, distribution and structural properties of the VL-II subhalo population in terms of both subhalo masses and maximum circular velocities. Then, we repopulate the original simulation with millions of subhaloes of masses down to about five orders of magnitude below the minimum VL-II subhalo mass (more than one order of magnitude in velocities). We compute subhalo DM annihilation astrophysical 'J-factors' and angular sizes for the entire subhalo population, by placing the Earth at a random position but at the right Galactocentric distance in the simulation. Thousands of these realizations are generated in order to obtain statistically meaningful results. We find that some nearby low-mass Galactic subhaloes, not massive enough to retain stars or gas, may indeed yield DM annihilation fluxes comparable to those expected from other, more massive and acknowledgeable DM targets like dwarf satellite galaxies. Typical angular sizes are of the order of the degree, thus subhaloes potentially appearing as extended sources in gamma-ray telescopes, depending on instrument angular resolution and sensitivity. Our work shows that low-mass Galactic subhaloes with no visible counterparts are expected to play a relevant role in current and future indirect DM search searches and should indeed be considered as excellent DM targets. [ABSTRACT FROM AUTHOR]

Nuclear star clusters (NSCs) are dense star clusters located at the centre of galaxies spanning a wide range of masses and morphologies. Analysing NSC occupation statistics in different environments provides an invaluable window into investigating early conditions of high-density star formation and mass assembly in clusters and group galaxies. We use HST/ACS deep imaging to obtain a catalogue of dwarf galaxies in two galaxy clusters in the Shapley supercluster: the central cluster Abell 3558 and the northern Abell 1736a. The Shapley region is an ideal laboratory to study nucleation as it stands as the highest mass concentration in the nearby Universe. We investigate the NSC occurrence in quiescent dwarf galaxies as faint as MI  = −10 mag and compare it with all other environments where nucleation data is available. We use galaxy cluster/group halo mass as a proxy for the environment and employ a Bayesian logistic regression framework to model the nucleation fraction (fn) as a function of galaxy luminosity and environment. We find a notably high fn in Abell 3558: at MI ≈ −13.1 mag, half the galaxies in the cluster host NSCs. This is higher than in the Virgo and Fornax clusters but comparable to the Coma Cluster. On the other hand, the fn in Abell 1736a is relatively lower, comparable to groups in the local volume. We find that the probability of nucleation varies with galaxy luminosity remarkably similarly in galaxy clusters. These results reinforce previous findings of the important role of the environment in NSC formation/growth. [ABSTRACT FROM AUTHOR]

Using cosmological hydrodynamical zoom-in simulations, we explore the properties of subhalos in Milky Way analogs that contain a subcomponent of atomic dark matter (ADM). ADM differs from cold dark matter (CDM) due to the presence of self-interactions that lead to energy dissipation, analogous to standard model baryons. This model can arise in dark sectors that are natural and theoretically motivated extensions to the standard model. The simulations used in this work were carried out using GIZMO and utilize the FIRE-2 galaxy formation physics in the standard model baryonic sector. For the parameter points we consider, the ADM gas cools efficiently, allowing it to collapse to the center of subhalos. This increases a subhalo's central density and affects its orbit, with more subhalos surviving small pericentric passages. The subset of subhalos that host satellite galaxies have cuspier density profiles and smaller stellar half-mass radii relative to CDM. The entire population of dwarf galaxies produced in the ADM simulations is more compact than those seen in CDM simulations, unable to reproduce the entire diversity of observed dwarf galaxy structures. Additionally, we also identify a population of highly compact subhalos that consist nearly entirely of ADM and form in the central region of the host, where they can leave distinctive imprints in the baryonic disk. This work presents the first detailed exploration of subhalo properties in a strongly dissipative dark matter scenario, providing intuition for how other regions of ADM parameter space, as well as other dark sector models, would impact galactic-scale observables. [ABSTRACT FROM AUTHOR]

We present a far-ultraviolet (FUV) study of 16 star-forming dwarf galaxies (SFDGs) using the Ultra Violet Imaging Telescope. Morphologically, SFDGs are classified as dwarf spirals, dwarf irregulars, and blue compact dwarfs (BCDs). We extracted the star-forming complexes (SFCs) from the sample galaxies, derived their sizes, and estimated the FUV + 24 μ m star-formation rates (SFRs). We also determined the approximate stellar disc mass associated with the SFCs using Infrared Array Camera 3.6 micron images. We derived the specific SFRs (sSFRs), as well as the SFR densities [Σ(SFR)] for the SFCs. We find that the lower Σ(SFR) for each type is different, with the dwarf irregulars having the lowest Σ(SFR) compared with others. However, the median size of the SFCs in the dwarf irregulars is the largest compared with the other two types when compared at roughly the same distance. We have derived the star-forming main sequence (SFMS) on the scale of SFCs for all three classes of SFDGs. We find that although all SFDGs approximately follow the global SFMS relation, i.e. SFR ∝ M *α (where globally α ≈ 1 for low-surface brightness galaxies and 0.9 for SFDGs), on the scale of SFCs the α value for each type is different. The α values for dwarf spirals, dwarf irregulars, and BCDs are found to be 0.74 ± 0.13, 0.87 ± 0.16, and 0.80 ± 0.19, respectively. However, the age of all SFCs approximately corresponds to 1 Gyr. Finally, we find that the outer SFCs in most galaxies except BCDs have a high sSFR, supporting the inside-out model of galaxy growth. [ABSTRACT FROM AUTHOR]

We present novel constraints on the underlying galaxy formation physics (e.g. mass-loading factor, star formation history, and metal retention) at z ≳ 7 for the low-mass (M * ∼ 105 M⊙) Local Group ultrafaint dwarf galaxy (UFD) Eridanus ii (Eri ii). Using a hierarchical Bayesian framework, we apply a one-zone chemical evolution model to Eri ii 's CaHK-based photometric metallicity distribution function (MDF; [Fe/H]) and find that the evolution of Eri ii is well characterized by a short, exponentially declining star formation history (⁠|$\tau _\text{SFH}=0.39\pm _{0.13}^{0.18}$| Gyr), a low star formation efficiency (⁠|$\tau _\text{SFE}=27.56\pm _{12.92}^{25.14}$| Gyr), and a large mass-loading factor (⁠|$\eta =194.53\pm _{42.67}^{33.37}$|⁠). Our results are consistent with Eri ii forming the majority of its stars before the end of reionization. The large mass-loading factor implies strong outflows in the early history of Eri ii and is in good agreement with theoretical predictions for the mass scaling of galactic winds. It also results in the ejection of >90 per cent of the metals produced in Eri ii. We make predictions for the distribution of [Mg/Fe]–[Fe/H] in Eri ii as well as the prevalence of ultra metal-poor stars, both of which can be tested by future chemical abundance measurements. Spectroscopic follow-up of the highest metallicity stars in Eri ii ([Fe/H] > −2) will greatly improve model constraints. Our new framework can readily be applied to all UFDs throughout the Local Group, providing new insights into the underlying physics governing the evolution of the faintest galaxies in the reionization era. [ABSTRACT FROM AUTHOR]

We use a suite of hydrodynamics simulations of the interstellar medium (ISM) within a galactic disk, which includes radiative transfer, a nonequilibrium model of molecular hydrogen, and a realistic model for star formation and feedback, to study the structure of the ISM and H2 abundance as a function of local ISM properties. We show that the star formation rate and structure of the ISM are sensitive to the metallicity of the gas with a progressively smoother density distribution with decreasing metallicity. In addition to the well-known trend of the H I– H 2 transition shifting to higher densities with decreasing metallicity, the maximum achieved molecular fraction in the ISM drops drastically at Z ≲ 0.2 Z ⊙ as the formation time of H2 becomes much longer than a typical lifetime of dense regions of the ISM. We present accurate fitting formulae for both volumetric and projected f H 2 measured on different scales as a function of gas metallicity, UV radiation field, and gas density. We show that when the formulae are applied to the patches in the simulated galaxy, the overall molecular gas mass is reproduced to better than a factor of ≲1.5 across the entire range of metallicities and scales. We also show that the presented fit is considerably more accurate than any of the previous f H 2 models and fitting formulae in the low-metallicity regime. The fit can thus be used for modeling molecular gas in low-resolution simulations and semi-analytic models of galaxy formation in the dwarf and high-redshift regimes. [ABSTRACT FROM AUTHOR]

We present ionizing spectra estimated at 13.6–100 eV for 10 dwarf galaxies with strong high-ionization lines of He ii λ 4686 and [Ne v ] λ 3426 ([Ne iv ] λ 2424) at z = 0 (z = 8) that are identified in our Keck/LRIS spectroscopy and the literature (the JWST Early Release Observations program). With the flux ratios of these high-ionization lines and >10 low-ionization lines of hydrogen, helium, oxygen, neon, and sulfur, we determine ionizing spectra consisting of stellar and nonthermal power-law radiation by photoionization modeling with free parameters of nebular properties, including metallicity and ionization parameter, canceling out abundance ratio differences. We find that all of the observed flux ratios are well reproduced by the photoionization models with the power-law index α EUV of α EUV ∼ (–1) − 0 and the luminosity L EUV of L EUV ∼ 1040–1042 erg s−1 at ∼55–100 eV for six galaxies, while four galaxies include large systematics in α EUV caused by stellar radiation contamination. We then compare α EUV and L EUV of these six galaxies with those predicted by the black hole (BH) accretion disk models and find that α EUV and L EUV are similar to those of the intermediate-mass BHs (IMBHs) in BH accretion disk models, albeit with possibilities of the other scenarios. Confirming these results with a known IMBH having a mass M BH of M BH = 105.75 M ⊙, we find that four local galaxies and one z = 7.665 galaxy have ionizing spectra consistent with those of IMBHs with M BH ∼ 103–105 M ⊙. [ABSTRACT FROM AUTHOR]

We study the size and structure of globular cluster (GC) systems of 118 early-type galaxies from the NGVS, MATLAS, and ACSVCS surveys. Fitting Sérsic profiles, we investigate the relationship between effective radii of GC systems (R e,gc) and galaxy properties. GC systems are 2–4 times more extended than host galaxies across the entire stellar mass range of our sample (108.3 M ⊙ < M * < 1011.6 M ⊙). The relationship between R e,gc and galaxy stellar mass exhibits a characteristic "knee" at a stellar mass of M p ≃ 1010.8, similar to the galaxy R e –stellar mass relationship. We present a new characterization of the traditional blue and red GC color subpopulations, describing them with respect to host galaxy (g ′ − i ′) color (Δgi): GCs with similar colors to their hosts have a "red" Δgi, and those significantly bluer GCs have a "blue" Δgi. The GC populations with red Δgi, even in dwarf galaxies, are twice as extended as the stars, suggesting that formation or survival mechanisms favor the outer regions. We find a tight correlation between R e,gc and the total number of GCs, with intrinsic scatter ≲0.1 dex spanning two and three orders of magnitude in size and number, respectively. This holds for both red and blue subpopulations, albeit with different slopes. Assuming that N GC,Total correlates with M 200, we find that the red GC systems have effective radii of roughly 1%–5% R 200, while the blue GC systems in massive galaxies can have sizes as large as ∼10% R 200. Environmental dependence on R e,gc is also found, with lower-density environments exhibiting more extended GC systems at fixed mass. [ABSTRACT FROM AUTHOR]

We present ionizing spectra estimated at 13.6–100 eV for 10 dwarf galaxies with strong high-ionization lines of He ii λ 4686 and [Ne v ] λ 3426 ([Ne iv ] λ 2424) at z = 0 (z = 8) that are identified in our Keck/LRIS spectroscopy and the literature (the JWST Early Release Observations program). With the flux ratios of these high-ionization lines and >10 low-ionization lines of hydrogen, helium, oxygen, neon, and sulfur, we determine ionizing spectra consisting of stellar and nonthermal power-law radiation by photoionization modeling with free parameters of nebular properties, including metallicity and ionization parameter, canceling out abundance ratio differences. We find that all of the observed flux ratios are well reproduced by the photoionization models with the power-law index α EUV of α EUV ∼ (–1) − 0 and the luminosity L EUV of L EUV ∼ 1040–1042 erg s−1 at ∼55–100 eV for six galaxies, while four galaxies include large systematics in α EUV caused by stellar radiation contamination. We then compare α EUV and L EUV of these six galaxies with those predicted by the black hole (BH) accretion disk models and find that α EUV and L EUV are similar to those of the intermediate-mass BHs (IMBHs) in BH accretion disk models, albeit with possibilities of the other scenarios. Confirming these results with a known IMBH having a mass M BH of M BH = 105.75 M ⊙, we find that four local galaxies and one z = 7.665 galaxy have ionizing spectra consistent with those of IMBHs with M BH ∼ 103–105 M ⊙. [ABSTRACT FROM AUTHOR]