Cosmological numerical simulations suggest that dSphs and dEs formed hierarchically via assembling much smaller stellar/gas clumps. Star formation had occurred intensively during the building up phase that is shorter than ∼1 Gyr. Dark matter assembled hierarchically, while gas collapsed dissipatively; as a result the metallicity gradient was built up and stars at the galaxy centre tend to have larger rotational velocity and smaller velocity dispersion. There are increasing evidences, however, that suggest rather long-lasted star formation in dwarf galaxies with much smaller SFRs, with which cosmological simulations need to be reconciled.

Using a sample of over 100 nucleated Virgo cluster dEs from the SDSS we show that interchanging nucleus and galaxy colours does not alter the colour-magnitude relation. No significant difference is found between nuclei and their parent galaxies in a multicolour comparison except for a weak tendency that some nuclei are slightly redder than their hosts.

We show that the extinction of quasar absorbers increases exponentially with the logarithmic column density of any volatile metal (e.g. zinc), with a characteristic turning point above which the quasars are severely dimmed. We derive the relation between extinction, HI column density ($N_\mathrm{HI}$), metallicity ($Z \equiv N_\mathrm{ZnII}/N_\mathrm{HI}$), and fraction of iron in dust [$f_\mathrm{Fe}(Z)$] in Damped Lyman $\alpha$ (DLA) systems. We use this relation to estimate the effect of dust obscuration on the statistical distributions of $N_\mathrm{HI}$ and $Z$ measured in magnitude-limited surveys of DLAs. In the redshift range where the measurements of zinc column densities have sufficient statistics ($1.8 \leq z \leq 3$) we find that the obscuration bias affects the shapes of the observed distributions. The metallicity distribution is particularly affected by the bias, which hampers the detection of DLA galaxies with near Solar metallicity. Our results perfectly reproduce, without tuning the dust parameters, the DLA observational threshold $\log N(\mathrm{ZnII})\,\mathrm{[cm^{-2}]} \lesssim 13.15$ found by Boissé and collaborators in 1998, in terms of a rapid rise of the obscuration. Our predictions of the effects of the bias on the statistics of DLAs are consistent with observational results obtained from unbiased surveys of radio-selected quasars.

We have examined some basic properties of damped Ly$\alpha$ systems (DLAs) by semi-analytic modelling. We assume that DLA hosts are disk galaxies whose mass function is generated by a Press-Schechter formalism at redshift 3. The disk undergoes star formation and chemical evolution. We select modelled DLAs according to their observational criterion by Monte Carlo simulation using random lines of sight and disk inclinations. The DLA ages are set to be 1 to 3 Gyr. By best-fitting the predicted metallicity distribution to the observed ones, we get the effective yield for DLAs of about $0.25Z_{\odot}$. On the basis of this constraint, we further compared our model predictions with observations at redshift 3 in the following properties: number density, gas content, HI frequency distribution, star formation rate density, and the relationship between metallicity and HI column density. We found that the predicted number density at redshift 3 agrees well with the observed value, but the gas content $\Omega_{DLA}$ is about 3 times larger than observed since our model predicts more DLA systems with higher column density. The frequency distribution at higher HI column density is quite consistent with observations while some difference exists at the lower HI end. The predicted star formation rate density contributed by DLAs is consistent with the most recent observations. In addition, we have investigated the connection between DLAs and Lyman Break galaxies (LBGs) by comparing their UV luminosity functions, which shows that DLAs host galaxies are much fainter than LBGs. However, there is a discrepancy between the model predictions and observations in the correlation between metallicity and HI column density for DLAs. Further investigations are needed into the mode of star formation in high redshift environments.

Dwarf galaxies tend to have a large spread in metal abundances and overall lower metallicites than large Spiral or Elliptical ones. Here we propose that if all stars are formed from an invariant canonical IMF within each star cluster which are distributed according to an embedded cluster mass function (ECMF), then the integrated stellar IMF over the whole galaxy (the integrated galaxial IMF, IGIMF) must be steeper than the canonical IMFs within the clusters, and additionally they must depended on the stellar mass of the galaxy. In particular, dwarf galaxies and low-surface brightness galaxies show steeper galaxial IMFs which vary strongly with the star-formation rate. The resulting number of Supernovae II per low-mass star, and the chemical enrichment history of these galaxies therefore vary substantially depending on the galaxy assembly history.

We present initial results from an high-resolution imaging search for damped Ly$\alpha$ absorbers toward the high-redshift quasar APM 08279+5255 by using the Adaptive Optics system (AO) attached to the Subaru telescope. We detected in total 11 objects within a $23''\times23''$ field around the quasar. Among these detected objects, we identified a possible candidate for the galaxy giving rise to the damped Ly$\alpha$ absorption at z$_{abs}$=2.974 with a criteria of distance from the sight-line toward the quasar and luminosity.

Thanks to the Sloan Digital Sky Survey, we now know that the Universe becomes opaque to Ly$\alpha$ photons at $z \sim 6$. This presents an obvious challenge for attempts to study the Universe at high redshifts with quasar absorption lines. I discuss two ways to extract more information about reionisation than the simple presence of complete Gunn-Peterson absorption. First, we still expect to see metal line absorption red-ward of Ly$\alpha$. This will allow us to probe the early phases of metal enrichment in the intergalactic medium; the lines can be quite strong because the enriched regions are relatively compact. This is particularly important because metals are a crucial feedback mechanism in the early Universe. Second, we expect to see isolated Ly$\alpha$ transmission features even before the final stages of reionisation. These features allow us to learn about the topology of reionisation and the condensation of the cosmic web at $z \sim 6$.

The intergalactic medium revealed by the numerous absorption lines seen in quasar spectra (the so-called Ly $\alpha$ forest) is believed to trace the potential wells of the dark matter. This is a unique tool to derive the power-spectrum of the initial fluctuations from high resolution and high S/N ratio spectra. One of the major limitations in these studies is the accuracy to which the quasar continuum is known. To investigate this problem, we have observed at intermediate spectral resolution ten bright and high redshift quasars (2.1 $< z_{em} <$ 4.7) that have also been observed with UVES. We shall compare the continuum determinations for both data sets.

I will review the progress of VLT spectroscopy of large numbers of individual stars in nearby dwarf spheroidal galaxies. This spectroscopy has allowed us to obtain detailed insights into the chemical and dynamical properties of the resolved stellar population in these nearby systems.

The physical state of the intergalactic medium can be probed in great detail with the intervening absorption systems seen in quasar spectra. The properties of the hydrogen absorbers depend on many cosmological parameters, such as the matter power spectrum, reionisation history, ionising background and the nature of the dark matter. The spectra also contain metal lines, which can be used to constrain the star formation history and the feedback processes acting in large and small galaxies. Simulations have been instrumental in investigating to what extent these parameters can be unambiguously constrained with current and future data. This paper is meant as an introduction to this subject, and reviews techniques and methods for simulating the intergalactic medium.

The Sloan Digital Sky Survey has recently discovered a coherent ring of stars at low galactic latitude that is believed to be the tidal stream of a merging dwarf galaxy in the Galactic plane (named the Monoceros tidal stream). The existence and location of the core of its progenitor galaxy is still controversial. The best candidate is the Canis Major dwarf galaxy, a distinct overdensity of red stars discovered in the 2MASS survey, but also interpreted as the signature of the Galactic warp viewed in projection. In this paper, we report a variety of new observational evidence that supports the notion that CMa is the remnant of a partially disrupted core of a dwarf satellite. The comparison of the orbit derived from our theoretical model for the parent galaxy of this ring-like structure with an accurate determination of CMa orbit leads to the conclusion that this satellite is the best candidate for the progenitor of the Monoceros tidal stream

In an effort to detect and understand the origin of large scale motions in the gaseous cosmic web at redshifts 2-4.5 we study the kinematics of the intergalactic medium from velocity shifts between absorption systems common to adjacent pairs of lines of sight to background QSO images. We establish the distribution of velocity shear between the lines of sight for different redshifts and transverse spatial separations up to 300 $h_{70}^{-1}$ physical kpc. Using a simple analytical model of Lyman $\alpha$ clouds as expanding pancakes, and a cosmological $\Lambda$CDM hydro-simulation we find that the observed distribution of velocity shear is consistent with an IGM expanding largely with the Hubble flow. The three dimensional distribution of expansion velocities in the hydro-simulation shows that the underlying velocity field is more complex than just simple expansion: the low density gaseous structures responsible for the Lyman $\alpha$ forest are mostly expanding somewhat faster than the Hubble flow, whereas few structures are undergoing gravitational contraction. We also briefly search for traces of galactic feedback and conclude that high redshift superwinds cannot be dominating the movements of the Ly$\alpha$ forest clouds at the observed epoch.

The recent discovery of hidden non-axysimmetric and disk-like structures in bright Virgo dwarf elliptical and lenticular galaxies (dE/dSph/dS0) indicates that they may have late-type progenitors. Using N-body simulations we follow the evolution of disk galaxies within a $\Lambda\textrm{CDM}$ cluster simulated with $10^7$ particles, where the hierarchical growth and galaxy harassment are modeled self-consistently. Most of the galaxies undergo significant morphological transformation, even at the outskirts of the cluster, and move through the Hubble sequence from late type disks to dwarf spheroidals. The time evolution of the simulated galaxies is compared with unsharp-masked images obtained from VLT data and the projected kinematics of our models with the latest high resolution spectroscopic studies from the Keck and Palomar telescopes.

Detailed studies of dwarf galaxies in the Local Group have revealed an amazing diversity in their star formation histories. Young and intermediate-age stellar populations are observed in some gas-poor dwarf ellipticals, like Fornax and Carina, where naively one would have expected to find preferentially old stellar populations. There are evidences that the environment might drive the evolution of these galaxies.

In order to explore stellar populations in dwarf galaxies in an environment denser than that of the Local Group we have observed 14 dwarf elliptical galaxies in Centaurus group in near-IR $J_s$ and $K_s$ bands. The intrinsic properties of these galaxies, the metallicities and ages of their stellar populations and the presence or absence of bright, intermediate-age AGB stars will be correlated with extrinsic properties like the local galaxy density. Here we summarize our observations, present the sample and show near-IR color-magnitude diagrams and luminosity functions for ESO269-066 and AM1343-452 dwarf galaxies.

We report the discovery of three new star clusters in the halo of the Local Group dwarf irregular galaxy NGC 6822. These clusters were found in the deep images taken with the MegaPrime at the CFHT covering a total field of 2 deg $\times$ 2 deg. The most remote cluster is found to be located as far as 79 arcmin away from the center of NGC 6822. This distance is several times larger than the size of the region in NGC 6822 where star clusters were previously found. Morphological structures of the clusters and color-magnitude diagrams of the resolved stars in the clusters show that at least two of these clusters are proabably old globular clusters.

We present preliminary results of a detailed analysis of the $z=3.55$ Lyman limit system observed in the optical spectrum of Q2000-330. We have fitted Voigt profiles to the system to determine the column densities and Doppler parameters of its many components. For its major components we have also determined the ionisation fraction of the gas and obtained crude estimates of metallicities. We find order of magnitude variations in ionisation fraction and metallicity in components separated by as little as 150 km s$^{-1}$ in velocity space. This work is presented as an example of a campaign we have begun to collect such information on a sample of $\sim 100$ such systems in an effort to accurately characterise this enigmatic and important class of quasar absorption line systems.

We present VLT-FORS1 color–magnitude diagrams (CMDs) reaching the oldest main-sequence turnoffs for three fields at two galactocentric distances in the Fornax dSph galaxy. We derive the star formation history (SFH) for each field through comparison with synthetic CMDs and show that the main epoch of star formation has extended to more recent epochs toward the center of the galaxy. A small burst of star formation about 2 Gyr ago is a robust feature in the SFH of all fields. It might be related to the shell structure found in Fornax by Coleman et al. (2004), which in turn has been interpreted as the relic of a merger event that occurred in Fornax about 2 Gyr ago.

The spatial distribution of the gas in the intergalactic medium and its physical properties can be recovered thanks to the characteristics of the Ly$\alpha$ absorption lines that are observed in the spectra of high redshift quasars, the so-called Ly$\alpha$ forest. We use inversion methods applied to a network of lines of sight to infer the topology of the intergalactic medium, based on reconstruction of the density field. The method has already been tested on simulated data.

The cosmological variability of $\alpha$ is probed from individual observations of pairs of Fe II lines. This procedure allows a better control of the systematics and avoids the influence of the spectral shifts due to ionisation inhomogeneities in the absorbers and/or non-zero offsets between different exposures. Applied to the Fe II lines of the metal absorption systems at $z_{\rm abs}=1.839$ in Q1101–264 and at $z_{\rm abs}=1.15$ in HE0515–4414 observed by means of UVES at the ESO-VLT, it provides $\Delta\alpha/\alpha = (0.4\pm1.5_{\rm stat})\times10^{-6}$. The result is shifted with respect to the Keck/HIRES mean $\Delta\alpha/\alpha = (-5.7\pm1.1_{\rm stat})\times10^{-6}$ (Murphy et al. 2004) at a high confidence level (95%). Full details of this work are given in Levshakov et al. (2005).

The meeting “Near Field Cosmology with Dwarf Elliptical Galaxies” covered a wide range of topics relating the general issues associated with galaxy formation and evolution as well as problems which are specific to spheroidal dwarfs. This paper summarizes these presentations in the form of an annotated guide to the presenters and their subjects. The results of the meeting demonstrate the value of focused, quantitative research on small galaxies as a way to enhance our understanding of how internal processes, cosmological foundations, and environmental conditions effect galaxy evolution.