For the full galaxy mass range, we find that previously observed trends of globular cluster (GC) system scaling parameters (number, luminosity or mass of all GCs in a galaxy normalized to the host galaxy luminosity or mass, e.g.SL) as a function of galaxy mass, holds irrespective of galaxy type or environment. The SL value of early-type galaxies is, on average, twice that of late-types. We derive theoretical predictions which describe remarkably well the observed GC system scaling parameter distributions given an assumed GC formation efficiency (η), i.e. the ratio of total mass in GCs to galaxy halo mass. It has a mean value of η ≃ 5.5 × 10−5, and increasing scatter toward low galaxy mass. The excess η-values of some massive galaxies compared to expectations from the mean model prediction, may be attributed to an efficient GC formation, inefficient production of field stars, accretion of low-mass high-η galaxies or likely a mixture of all these effects.

We present the internal kinematics of UCD3, the brightest known ultra-compact dwarf galaxy (UCD) in the Fornax cluster and the first UCD with spatially resolved spectroscopy. Based on seeing-limited observations with VLT/FLAMES, we measure a velocity field showing the signature of weak rotation and a radial velocity dispersion profile that is flatter than expected from an isotropic Jeans model where mass follows light. We find that both, a strongly anisotropic velocity distribution, and a dark matter component as predicted by simulations of galaxy threshing, can explain the observed flattening.

We studied the stellar population in M 32 by means of full spectral fitting. Three different galactic radii were analysed, from the nuclear region out to 2 arcmin from the centre. As a main result we propose that an ancient and an intermediate-age population co-exist in M 32, and that the balance between these two populations change between the nucleus and outside one effective radius in the sense that the contribution from the intermediate population is larger at the nuclear region. We retrieve a smaller signal of a young population at all radii whose origin is unclear.

We present the deepest optical CMD to date of M 32, obtained from HST ACS/HRC images. The dominant feature is the RC, whose CMD location suggests a mean age between 8 and 10 Gyr for [Fe/H] = −0.2 in M 32. We detect for the first time the RGB and AGB bumps in M 32 which constrain its mean age to be 5–10 Gyr old at 2′ from the center. Bright AGB stars indicate the presence of intermediate-age populations. A detected blue component of stars may indicate for the first time the presence of a young stellar population of ~0.5 Gyr in our M 32 field. However, it is likely that the younger stars of this blue plume belong to M 31 rather than to M 32. The fainter stars populating the blue plume indicate the presence of stars not younger than 1 Gyr and/or blue straggler stars in M 32.

We present detailed chemical abundances of Fe, Ca and Ba for 17 globular clusters (GCs) in 5 Local Group dwarf galaxies: NGC 205, NGC 6822, WLM, the SMC and LMC. These abundances are part of a larger sample of over 20 individual elements measured in GCs in these galaxies using a new analysis method for high resolution, integrated light spectra. Our analysis also provides age and stellar population constraints. The existence of GCs in dwarf galaxies with a range of ages implies that there were episodes of rapid star formation (SF) throughout the history of these galaxies; the abundance ratios of these clusters suggest that the duration of these burst varied considerably from galaxy to galaxy. We find evolution of Fe, Ca, and Ba with age in the LMC, SMC, and NGC 6822 that is consistent with extended, lower-efficiency SF between bursts, with an increasing contribution of low-metallicity AGB ejecta at late times. Our sample of GCs in NGC 205 and WLM are predominantly old and metal-poor with high [Ca/Fe] ratios, implying that the early history of these galaxies was marked by consistently high SF rates.

With targeted imaging of groups in the local volume, the regions of collapse around bright galaxies can be clearly identified by the distribution of dwarfs and luminosity functions can be established to very faint levels. In the case of the M 81 Group there is completion to MR ~ −9. In all well studied cases, the faint end slopes are in the range − 1.35 < α < −1.2, much flatter than the slope for the bottom end of the halo mass spectrum anticipated by ΛCDM hierarchical clustering theory. Small but significant variations are found with environment. Interestingly, the populations of dwarf galaxies are roughly constant per unit halo mass. With the numbers of dwarfs as an anchor point, evolved environments (dominated by early morphological types) have relatively fewer intermediate luminosity systems and at least one relatively more important galaxy at the core. The variations with environment are consistent with a scenario of galaxy merging. However it is questionable if the universal dearth of visible dwarf systems is a consequence of an astrophysical process like reionization.

We present a project on study of groups composed of dwarf galaxies only. We selected such structures using HyperLEDA and NED databases with visual inspection on SDSS images and on digital copy of POSS. The groups are characterized by size of few tens of kpc and line-of-sight velocity dispersion about 18 km s−1. Our groups similar to associations of nearby dwarfs from Tully et al. (2006). This specific population of multiple dwarf galaxies such as I Zw 18 may contain significant amount of dark matter. It is very likely that we see them at the stage just before merging of its components.

The HST/ACS Coma Cluster Treasury Survey addresses many outstanding issues concerning galaxy formation, and provides a fundamental low-redshift reference, and comparison dataset for cluster studies at high redshift. We present preliminary results from our follow-up Keck/DEIMOS spectroscopic survey, which targets galaxies in the dense cluster core. Accurate velocity dispersions for 41 cluster dwarf galaxies were measured. These were selected from CFHT and HST/ACS images. Combined with accurate structural information, velocity dispersions facilitate a detailed analysis of the fundamental galaxy “scaling laws” for cluster dwarf galaxies. We investigate the behaviour of velocity dispersion with metallicity, by measuring absorption line indices for the 15 brightest cluster dwarfs. These observations help constrain galaxy formation models and provide further insight into the formation and evolution of dwarf galaxies in dense environments.

Dwarf galaxies dominate the galaxy luminosity function, yet their contribution to the baryonic mass function is not well determined. Photometric gas fraction estimators allow us to obtain neutral atomic gas masses for statistical samples of galaxies to help constrain the baryonic mass function. We adapt the photometric gas fraction technique to be more useful for predicting gas masses of dwarf galaxies.

We present ultraviolet (UV) properties of dwarf galaxies in the Fornax and Ursa Major clusters in comparison with the Virgo cluster. Most of the dwarf galaxies in the Fornax cluster show red UV colors which is consistent with that the Fornax is dynamically evolved cluster with large fraction of early-type galaxies. Meanwhile, majority of dwarf galaxies of Ursa Major cluster are late-type with blue UV colors, indicating prevalence of strong star formation activities in the low density environment.

We present a study of the bar fraction in the Coma cluster galaxies based on a sample of ~190 galaxies selected from the SDSS-DR6 and observed with the Hubble Space Telescope (HST) Advanced Camera for Survey (ACS). We explore the presence of bars, detected by visual classification, throughout an unprecedented luminosity range of 9 mag (− 23 < Mr < −14). We find that bars are hosted by galaxies in a tight range of both luminosities (−22 < Mr < −17) and masses (109 < M∗/M⊙ < 1011). We find also that the bar fraction does not vary significantly with the distance to the cluster center, implying that cluster environment plays a second-order role in bar formation/evolution. The shape of the bar fraction distribution with respect to both luminosity and mass is well matched by the luminosity distribution of disk galaxies in Coma, indicating that bars are good tracers of cold stellar disks.

We study the fundamental and the photometric plane of a sample of ~50 dwarf galaxies within the core of Coma cluster observed with DEIMOS on Keck II down to MR ~−15 Mag. We also carried out a galaxy structure modeling using the HST/ACS I-band images for a larger sample. We found larger velocity dispersions for fainter dwarfs than what expected from mass-luminosity trends of brighter Coma galaxies. In addition, fainter galaxies do not lie on the fundamental plane of brighter dwarfs and their deviations from the fundamental plane increases as their luminosities, central velocity dispersions and Sérsic indices decrease. We also noticed that those faint galaxies, which are outliers in the fundamental plane relation, have excess light at their central region with respect to their corresponding Sérsic model.

The environmental effects on galaxy evolution have recently been disputed based on large SDSS galaxy samples but these effects are still expected to be strong for low-mass galaxies. We obtained deep near-infrared imaging of irregular dwarfs in Cen A, M 81 and Sculptor groups – spanning a range of galaxy density, – and we study the properties of these dwarfs, i.e. abundance, chemical evolution, and structural parameters. Here we give a preliminary assessment of the structural parameters for these galaxies.

We present a new approach to estimate the ages of very young clusters based on the Pre-Main Sequence (PMS) Turn-On (TOn), point in the colour magnitude diagram where the PMS joins the main sequence (MS). In order to detect the TOn magnitude, we propose to monitor the spatial distribution of MS stars: any drop in the MS spatial density is a necessary signature for a successful TOn identification and, accordingly, a robust cluster dating. We use Hubble Space Telescope photometry of the star forming region NGC 346 as a benchmark for the method.

In recent years the census of known satellites in our own Local Group and in nearby galaxy groups has increased substantially due to sensitive wide-area surveys. In the Local Group these surveys have more than doubled its galaxy content and extended the galaxy luminosity function to very faint total magnitudes. Deep ground-based imaging and spectroscopic observations as well as high-resolution imaging with the Hubble Space Telescope have revolutionized our understanding of the chemical evolution and star formation histories of the satellites. We often find long-lasting star formation episodes with low star formation efficiencies. There is evidence for localized, stochastic enrichment, and recent searches are now beginning to uncover even extremely metal-deficient stars. In many satellites evidence for two or more distinct stellar subpopulations is found. Differing fractions of old populations have been detected in all satellites studied in sufficient detail so far. Kinematic measurements support a picture in which satellites are dark-matter dominated, although recent results indicate that the proposed common mass scale may not hold for very low-mass satellites. When considering satellite ensembles, we find global morphology–distance and gas-content–distance relations in all groups studied thus far, but individual star formation histories seem to also strongly depend on a given satellite’s intrinsic properties.

We present the first systematic comparison of the detailed properties, including internal kinematics, chemical abundances, sizes, and dark matter masses, of Milky Way and M 31 dSphs as a part of the SPLASH Survey (Spectroscopic and Photometric Landscape of Andromeda’s Stellar Halo). Through Keck/DEIMOS spectroscopy of several hundred individual red giants in a half dozen M 31 galaxies, our results indicate both similarities and differences between the family of dSphs in the Milky Way and M 31. For example, we find that the luminosity-metallicity relation of dSphs in the two hosts is very similar between L = 105 and 107 L⊙, the size distribution of M 31 dSphs extends to larger values at the same luminosity compared to Milky Way counterparts (especially at the bright end), and that the dark matter masses of M 31 dSphs are slightly smaller than similar luminosity Milky Way galaxies.

We studied the impact of the revisited values for the LSR circular velocity of the Milky Way (Reid et al. 2004) on the formation of the Magellanic Stream. The LSR circular velocity was varied within its observational uncertainties as a free parameter of the interaction between the Large (LMC) and the Small (SMC) Magellanic Clouds and the Galaxy. We have shown that the large–scale morphology and kinematics of the Magellanic Stream may be reproduced as tidal features, assuming the recent values of the proper motions of the Magellanic Clouds (Kallivayalil  2006). Automated exploration of the entire parameter space for the interaction was performed to identify all parameter combinations that allow for modeling the Magellanic Stream. Satisfactory models exist for the dynamical mass of the Milky Way within a wide range of 0.6 ⋅ 1012 M⊙ to 3.0 ⋅ 1012 M⊙ and over the entire 1–σ errors of the proper motions of the Clouds. However, the successful models share a common interaction scenario. The Magellanic Clouds are satellites of the Milky Way, and in all cases two close LMC–SMC encounters occurred within the last 4 Gyr at t < −2.5 Gyr and t ≈ −150 Myr, triggering the formation of the Stream and of the Magellanic Bridge, respectively. The latter encounter is encoded in the observed proper motions and inevitable in any model of the interaction. We conclude that the tidal origin of the Magellanic Stream implies the previously introduced LMC/SMC orbital history, unless the parameters of the interaction are revised substantially.

The Next Generation Virgo Cluster Survey (NGVS) is a CFHT Large Program that is using the wide field of view capabilities of the MegaCam camera to map the entire Virgo Cluster from its core to virial radius. The observing strategy has been optimized to detect very low surface brightness structures in the cluster, including intracluster stellar streams and faint dwarf spheroidal galaxies. We present here the current status of this ongoing survey, with an emphasis on the detection and analysis of the very low-mass galaxies in the cluster that have been revealed by the NGVS.

It has been suggested that the outer young Galactic halo globular cluster population might be associated (or even the nuclei) to tidal disrupted dwarf spheroidals, now extinct galaxies. If this hypothesis is true, these systems might be still surrounded by a distinct and detectable stellar population similar to that of their progenitor galaxies. We have designed a systematic photometric survey of Galactic globular clusters to unveil the possible remnants of the systems where they were formed and estimate their contribution to the Galatic halo.

With the new generation of wide-field surveys, our understanding of the Andromeda satellite system has dramatically improved in recent years. Since 2004, 12 new dwarf galaxies have been discovered around Andromeda, doubling the number of previously known companions. What are the properties of these newly discovered dwarfs and what do they tell us about galaxy formation? Are these systems bound? Do they show evidence of multiple star formation epochs? To better understand the stellar populations of the faintest dwarfs around M 31, we have used the Large Binocular Camera (LBT) and Suprime-Cam (Subaru) to obtain photometric observations of And X, And XVII, And XVIII, And XIX, And XX, And XXI and And XXII. Reaching below the horizontal branch, these observations have allowed for accurate distance determinations to be made, together with metallicity estimates based on the red giant branch stars. Our analysis shows our 7 dwarfs to be metal poor and with large spreads in [Fe/H], it strongly suggests multiple generations of stars are present in And X, And XVII, And XVIII, and And XIX, And XXI.