A number of mechanisms have been proposed to connect star-forming dwarf irregular galaxies with the formation of non-star-forming dwarf spheroidal galaxies, but distinguishing between these mechanisms has been difficult. We use the Via Lactea dark matter only cosmological simulations to test two well-motivated simple hypotheses---transformation of irregulars into dwarf spheroidal galaxies by tidal stirring and ram pressure stripping following a close passage to the host galaxy, and transformation via mergers between dwarfs---and predict the radial distribution and inferred formation times of the resulting dwarf spheroidal galaxies. We compare this to the observed distribution in the Local Group and show that 1) the observed dSph distribution far from the Galaxy or M31 can be matched by the VL halos that have passed near the host galaxy at least once, though significant halo-to-halo scatter exists, 2) models that require two or more pericenter passages for dSph-formation cannot account for the dSphs beyond 500 kpc such as Cetus and Tucana, and 3) mergers predict a flat radial distribution of dSphs and cannot account for the high dSph fraction near the Galaxy, but are not ruled out at large distances. The models also suggest that for dSphs found today beyond 500 kpc, mergers tend to occur significantly earlier than dwarf--host encounters, thus leading to a potentially observable difference in stellar populations. We argue that tidal interactions are sufficient to reproduce the observed distribution of dSphs if and only if a single pericenter passage is sufficient to form a dSph.
We study dwarf satellite galaxy quenching using observations from the Geha et al. (2012) NSA/SDSS catalog together with LCDM cosmological simulations to facilitate selection and interpretation. We show that fewer than 30% of dwarfs (M* ~ 10^8.5-10^9.5 Msun) identified as satellites within massive host halos (Mhost ~ 10^12.5-10^14 Msun) are quenched, in spite of the expectation from simulations that half of them should have been accreted more than 6 Gyr ago. We conclude that whatever the action triggering environmental quenching of dwarf satellites, the process must be highly inefficient. We in…
In the Local Group, nearly all of the dwarf galaxies (M_star < 10^9 M_sun) that are satellites within 300 kpc (the virial radius) of the Milky Way (MW) and Andromeda (M31) have quiescent star formation and little-to-no cold gas. This contrasts strongly with comparatively isolated dwarf galaxies, which are almost all actively star-forming and gas-rich. This near dichotomy implies a rapid transformation of satellite dwarf galaxies after falling into the halos of the MW or M31. We combine the observed quiescent fractions for satellites of the MW and M31 with the infall times of satellites from th…
Confronting fuzzy dark matter with the rotation curves of nearby dwarf irregular galaxies
Instituto de Astrofísica de Canarias（加那利群岛天体物理研究所）；Universidad de La Laguna（拉奥罗哈大学）；Università di Padova（帕多瓦大学）；INFN-Padova（意大利国家核物理研究所帕多瓦分部）；INAF-Padova（意大利国家天体物理研究所帕多瓦分部）
We present new constraints on the star formation histories of six ultra-faint dwarf galaxies: Bootes I, Canes Venatici II, Coma Berenices, Hercules, Leo IV, and Ursa Major I. Our analysis employs a combination of high-precision photometry obtained with the Advanced Camera for Surveys on the Hubble Space Telescope, medium-resolution spectroscopy obtained with the DEep Imaging Multi-Object Spectrograph on the W.M. Keck Observatory, and updated Victoria-Regina isochrones tailored to the abundance patterns appropriate for these galaxies. The data for five of these Milky Way satellites are best fit…
We explore the variation in stellar population ages for Coma cluster galaxies as a function of projected cluster-centric distance, using a sample of 362 red-sequence galaxies with high signal-to-noise spectroscopy. The sample spans a wide range in luminosity (0.02-4 L*) and extends from the cluster core to near the virial radius. We find a clear distinction in the observed trends of the giant and dwarf galaxies. The ages of red-sequence giants are primarily determined by galaxy mass, with only weak modulation by environment, in the sense that galaxies at larger cluster-centric distance are sli…
We present the cumulative star-formation histories (SFHs) of >15000 dwarf galaxies ($M_{*}=10^{7-10}M_{\odot}$) from the TNG50 run of the IllustrisTNG suite across a vast range of environments. The key factors determining the dwarfs' SFHs are their status as central or satellite and their stellar mass, with centrals and more massive dwarfs assembling their stellar mass at later times on average compared to satellites and lower mass dwarfs. The satellites (in hosts of total mass $M_{200c,\,host}=10^{12-14.3}M_{\odot}$) assembled 90% of their z=0 stellar mass ~$7.0_{-5.5}^{+3.3}$ Gyr ago, while …
A hydrodynamical CLONE of the Virgo cluster: II. Confronting observed and synthetic galaxy population twins in a dense environment
Univ. Lille, CNRS, Centrale Lille, UMR 9189 CRIStAL（里尔大学）；Université Paris-Saclay, CNRS, Institut d’Astrophysique Spatiale（巴黎萨克雷大学）；University of Birmingham School of Physics and Astronomy（伯明翰大学）；Institut d’Astrophysique de Paris, UMR 7095, Sorbonne Université, CNRS（索邦大学）；Univ Lyon, Univ Lyon1, Ens de Lyon, CNRS, Centre de Recherche Astrophysique de Lyon UMR5574（里昂大学）；Universidad Autónoma de Madrid（马德里自治大学）；International Centre for Radio Astronomy Research, University of Western Australia（西澳大利亚大学）
We demonstrate that dwarf galaxies (10^7 < M_stellar < 10^9 Msun) with no active star formation are extremely rare (<0.06%) in the field. Our sample is based on the NASA-Sloan Atlas which is a re-analysis of the Sloan Digital Sky Survey Data Release 8. We examine the relative number of quenched versus star forming dwarf galaxies, defining quenched galaxies as having no Halpha emission (EW_Halpha < 2 AA) and a strong 4000AA-break. The fraction of quenched dwarf galaxies decreases rapidly with increasing distance from a massive host, leveling off for distances beyond 1.5 Mpc. We define galaxies …
The Lambda Cold Dark Matter (LCDM) paradigm makes specific predictions for the abundance, structure, substructure and clustering of dark matter halos, the sites of galaxy formation. These predictions can be directly tested, in the low-mass halo regime, by dark matter-dominated dwarf galaxies. A number of potential challenges to LCDM have been identified when confronting the expected properties of dwarfs with observation. I review our understanding of a few of these issues, including the `missing satellites' and the `too-big-to-fail' problems, and argue that neither poses an insurmountable chal…
We analyse Spitzer MIPS 24micron observations, and SDSS (DR7) optical broadband photometry and spectra, to investigate the star formation (SF) properties of galaxies residing in the Coma supercluster region. We find that SF in dwarf galaxies is quenched only in the high density environment at the centre of clusters and groups, but passively-evolving massive galaxies are found in all environments, indicating that massive galaxies can become passive via internal processes. We find AGN activity is suppressed in the cluster cores. We present evidence for a strong dependence of the mechanism(s) res…
We apply the empirical galaxy--halo connection model UniverseMachine to dark matter-only zoom-in simulations of isolated Milky Way (MW)--mass halos along with their parent cosmological simulations. This application extends \textsc{UniverseMachine} predictions into the ultra-faint dwarf galaxy regime ($ 10^{2}\,\mathrm{M_{\odot}} \leqslant M_{\ast} \leqslant 10^{5}\,\mathrm{M_{\odot}}$) and yields a well-resolved stellar mass--halo mass (SMHM) relation over the peak halo mass range $10^8\,\mathrm{M_{\odot}}$ to $10^{15}\,\mathrm{M_{\odot}}$. The extensive dynamic range provided by the zoom-in s…
We demonstrate how the least luminous galaxies in the Universe, ultra-faint dwarf galaxies, are sensitive to their dynamical mass at the time of cosmic reionization. We select a low-mass ($\sim \text{1.5} \times 10^{9} \, \text{M}_{\odot}$) dark matter halo from a cosmological volume, and perform zoom hydrodynamical simulations with multiple alternative histories using "genetically modified" initial conditions. Earlier forming ultra-faints have higher stellar mass today, due to a longer period of star formation before their quenching by reionization. Our histories all converge to the same fina…
A key unknown of the Milky Way (MW) satellites is their orbital history, and, in particular, the time they were accreted onto the MW system since it marks the point where they experience a multitude of environmental processes. We present a new methodology for determining infall times, namely using a neural network (NN) algorithm. The NN is trained on MW-analogues in the EAGLE hydrodynamical simulation to predict if a dwarf galaxy is at first infall or a backsplash galaxy and to infer its infall time. The resulting NN predicts with 85\% accuracy if a galaxy currently outside the virial radius i…
Star formation is observed to be suppressed in group and cluster galaxies compared to the field. To gain insight into the quenching process, we have analysed ~2000 galaxies formed in the GIMIC suite of cosmological hydrodynamical simulations. The time of quenching varies from ~2 Gyr before accretion (first crossing of r200,c) to >4 Gyr after, depending on satellite and host mass. Once begun, quenching is rapid (>~ 500 Myr) in low-mass galaxies (M* < 10^10 M_Sun), but significantly more protracted for more massive satellites. The simulations predict a substantial role of outflows driven by ram …
We examine the effects of pre-processing across the Coma Supercluster, including 3505 galaxies over 500 sq deg, by quantifying the degree to which star-forming (SF) activity is quenched as a function of environment. We characterise environment using the complementary techniques of Voronoi Tessellation, to measure the density field, and the Minimal Spanning Tree, to define continuous structures, and so we measure SF activity as a function of local density and the type of environment (cluster, group, filament, and void), and quantify the degree to which environment contributes to quenching of SF…
Galaxies and their dark-matter halos have posed several challenges to the Dark Energy plus Cold Dark Matter (LCDM) cosmological model. These discrepancies between observations and theory intensify for the lowest-mass (`dwarf') galaxies. LCDM predictions for the number, spatial distribution, and internal structure of low-mass dark-matter halos have historically been at odds with observed dwarf galaxies, but this is partially expected, because many predictions modeled only the dark-matter component. Any robust LCDM prediction must include, hand-in-hand, a model for galaxy formation to understand…
The vast majority of low-mass satellite galaxies around the Milky Way and M31 appear virtually devoid of cool gas and show no signs of recent or ongoing star formation. Cosmological simulations demonstrate that such quenching is expected and is due to the harsh environmental conditions that satellites face when joining the Local Group (LG). However, recent observations of Milky Way analogues in the SAGA survey present a very different picture, showing the majority of observed satellites to be actively forming stars, calling into question the realism of current simulations and the typicality of…
While low mass, star forming galaxies are often considered as the primary driver of reionization, their actual contribution to the cosmic ultraviolet background is still uncertain, mostly because the escape fraction of ionizing photons is only poorly constrained. Theoretical studies have shown that efficient supernova feedback is a necessary condition to create paths through which ionizing radiation can escape into the intergalactic medium. We investigate the possibility that accreting supermassive black holes in early dwarf galaxies may provide additional feedback and enhance the leakage of i…
We present results from a resolved stellar population search for dwarf satellite galaxies of six nearby (D $<5$ Mpc), sub-Milky-Way mass hosts using deep ($m\sim27$ mag) optical imaging from the Large Binocular Telescope. We perform image simulations to quantify our detection efficiency for dwarfs over a large range in luminosity and size, and develop a fast catalog-based emulator that includes a treatment of unresolved photometric blending. We discover no new dwarf satellites, but we recover two previously known dwarfs (DDO 113 and LV J1228+4358) with $M_{\text{V}}<-12$ that lie in our survey…
We use dust scaling relations to investigate the hypothesis that Virgo cluster transition-type dwarfs are infalling star-forming field galaxies, which is argued based on their optical features (e.g. disks, spiral arms, bars) and kinematic properties similar to late-type galaxies. After their infall, environmental effects gradually transform them into early-type galaxies through the removal of their interstellar medium and quenching of all star formation activity. In this paper, we aim to verify whether this hypothesis holds using far-infrared diagnostics based on Herschel observations of the V…
We investigate the population of dwarf galaxies with stellar masses similar to the Large Magellanic Cloud (LMC) and M33 in the EAGLE galaxy formation simulation. In the field, galaxies reside in haloes with stellar-to-halo mass ratios of $1.03^{+0.50}_{-0.31}\times10^{-2}$ (68% confidence level); systems like the LMC, which have an SMC-mass satellite, reside in haloes about 1.3 times more massive, which suggests an LMC halo mass at infall, $M_{200}=3.4^{+1.8}_{-1.2}\times10^{11}M_\odot$ (68% confidence level). The colour distribution of dwarfs is bimodal, with the red galaxies ($g-r>0.6$) bein…
We present a deep Hubble Space Telescope (HST) imaging study of two dwarf galaxies in the halos of Local Volume Large Magellanic Cloud (LMC) analogs. These dwarfs were discovered as part of our Subaru+Hyper Suprime-Cam MADCASH survey: MADCASH-1, which is a satellite of NGC 2403 (D~3.2 Mpc), and MADCASH-2, a previously unknown dwarf galaxy near NGC 4214 (D~3.0 Mpc). Our HST data reach >3.5 mag below the tip of the red giant branch (TRGB) of each dwarf, allowing us to derive their structural parameters and assess their stellar populations. We measure TRGB distances ($D=3.41^{+0.24}_{-0.23}$ Mpc …
We present new medium resolution kinematic data for a sample of 21 dwarf early-type galaxies (dEs) mainly in the Virgo cluster, obtained with the WHT and INT telescopes at the Roque de los Muchachos Observatory (La Palma, Spain). These data are used to study the origin of the dwarf elliptical galaxy population inhabiting clusters. We confirm that dEs are not dark matter dominated galaxies, at least up to the half-light radius. We also find that the observed galaxies in the outer parts of the cluster are mostly rotationally supported systems with disky morphological shapes. Rotationally support…
Dwarf spheroidal galaxies (dSphs) are extremely gas-poor, dark matter-dominated galaxies, which make them ideal to test the predictions of the cold dark matter (CDM) model. We argue that the removal of the baryonic component from gas-rich dwarf irregular galaxies, the progenitors of dSphs, can substantially reduce their central density. Thus, it may play an important role in alleviating one of the problems of the CDM model related to the structure of relatively massive satellite galaxies of the Milky Way (MW). Traditionally, collisionless cosmological N-body simulations are used when confronti…
We present new observational results on the kinematical, morphological, and stellar population properties of a sample of 21 dEs located both in the Virgo cluster and in the field, which show that 52% of the dEs i) are rotationally supported, ii) exhibit structural signs of typical rotating systems such as discs, bars or spiral arms, iii) are younger (~3 Gyr) than non-rotating dEs, and iv) are preferentially located either in the outskirts of Virgo or in the field. This evidence is consistent with the idea that rotationally supported dwarfs are late type spirals or irregulars that recently ente…
(Abridged) AVOCADO aims at establishing firm conclusions on the formation and evolution of dwarf galaxies by constructing and analysing a homogeneous, multiwavelength dataset for a statistically significant sample of approximately 6500 nearby dwarfs (M_i > -18 mag). We present the sample selection criteria and describe the suite of analysis tools, some of them developed in the framework of the Virtual Observatory. We make use of optical spectra and UV-to-NIR imaging of the dwarf sample to derive SFRs, stellar masses, ages and metallicities - which are further supplemented with structural param…
We use cosmological simulations to identify dark matter subhalo host candidates of the Fornax dwarf spheroidal galaxy using the stellar kinematic properties of Fornax. We consider cold dark matter (CDM), warm dark matter (WDM), and decaying dark matter (DDM) simulations for our models of structure formation. The subhalo candidates in CDM typically have smaller mass and higher concentrations at z = 0 than the corresponding candidates in WDM and DDM. We examine the formation histories of the ~ 100 Fornax candidate subhalos identified in CDM simulations and, using approximate luminosity-mass rela…
Based on Hubble Space Telescope observations from the Local Cosmology from Isolated Dwarfs project, we present the star formation histories, as a function of galactocentric radius, of four isolated Local Group dwarf galaxies: two dSph galaxies, Cetus and Tucana, and two transition galaxies (dTrs), LGS-3 and Phoenix. The oldest stellar populations of the dSphs and dTrs are, within the uncertainties, coeval ($\sim 13 Gyr$) at all galactocentric radii. We find that there are no significative differences between the four galaxies in the fundamental properties (such as the normalized star formation…
We present optical imaging and spectroscopy and HI imaging of the Virgo Cluster galaxy IC 3418, which is likely a "smoking gun" example of the transformation of a dwarf irregular into a dwarf elliptical galaxy by ram pressure stripping. IC 3418 has a spectacular 17 kpc length UV-bright tail comprised of knots, head-tail, and linear stellar features. The only H-alpha emission arises from a few HII regions in the tail, the brightest of which are at the heads of head-tail UV sources whose tails point toward the galaxy ("fireballs"). Several of the elongated tail sources have H-alpha peaks outward…
We present a demographic analysis of integrated star formation and gas properties for a sample of galaxies representative of the overall population at z~0. This research was undertaken in order to characterise the nature of star formation and interstellar medium behaviour in the local universe, and test the extent to which global star formation rates can be seen as dependent on the interstellar gas content. Archival 21 cm derived HI data are compiled from the literature, and are combined with CO (J=1-0) derived H_2 masses to calculate and characterise the total gas content for a large sample o…
We use archival HST observations of resolved stellar populations to derive the star formation histories (SFHs) of 18 nearby starburst dwarf galaxies. In this first paper we present the observations, color-magnitude diagrams, and the SFHs of the 18 starburst galaxies, based on a homogeneous approach to the data reduction, differential extinction, and treatment of photometric completeness. We adopt a star formation rate (SFR) threshold normalized to the average SFR of the individual system as a metric for classifying starbursts in SFHs derived from resolved stellar populations. This choice facil…
We present IRAM 30m sensitive upper limits on CO emission in the ram pressure stripped dwarf Virgo galaxy IC3418 and in a few positions covering HII regions in its prominent 17 kpc UV/Ha gas-stripped tail. In the central few arcseconds of the galaxy, we report a possible marginal detection of about 1x10^6 M_sun of molecular gas (assuming a Galactic CO-to-H_2 conversion factor) that could correspond to a surviving nuclear gas reservoir. We estimate that there is less molecular gas in the main body of IC3418, by at least a factor of 20, than would be expected from the pre-quenching UV-based star…
