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.

We find evidence for dust in the intervening QSO absorbers from the spectra of QSOs in the Sloan Digital Sky Survey Data Release 1. No evidence is found for the 2175 Å feature which is present in the Milky Way dust extinction curve.

With the information era in astronomy coming, this “data avalanche” may provide many answers to important problems in contemporary astrophysics. The most important problem is sifting through massive amounts of data to mine knowledge. In this paper, we positionally cross-identify multi-wavelength data from optical, near-infrared, and X-ray bands, and then employ Alternating Decision Trees (ADTree) to quickly and robustly separate AGN candidates to a high degree of accuracy. We emphasise the application of the method due to the development of large survey projects and the establishment of the virtual observatory, and conclude that the application of data mining algorithms in astronomy is of great importance to discover new knowledge impossible to obtain before, and promote the development of astronomy.

I review current results from searching for galaxies giving rise to damped Ly$\alpha$ absorbers (DLAs) at $z<1$. Using 14 confirmed DLA galaxies, I further show that intermediate-redshift galaxies possess a large H I envelope out to $24-30\ h^{-1}$ kpc in radius. The photometric and spectral properties of these galaxies confirm that DLA galaxies are drawn from the typical field population, and not from a separate population of low surface brightness or dwarf galaxies. The spatial distribution of metals in the cold ISM of intermediate-redshift galaxies is characterised by a radial gradient of $-0.041\pm 0.012$ dex per kiloparsec (or equivalently a scale length of $10.6\ h^{-1}$ kpc) to $30\ h^{-1}$ kpc radius based on an ensemble of six galaxy-DLA pairs. Adopting this abundance gradient and known $N({\rm H I})$ profiles of nearby galaxies, I show that the observed low metal content of the DLA population can arise naturally as a combination of gas cross-section selection and metallicity gradients commonly observed in local disk galaxies.

We use cosmological sph simulations to investigate the effects of mergers and interactions on the formation of the bulge and disc components of galactic systems. We find that secular evolution during mergers seems to be a key process in the formation of stable disc-bulge systems with observational counterparts and contributes to establish the fundamental relations observed in galaxies. Our findings suggest that the secular evolution phase couples the formation mechanisms of the bulge and disc components. According to our results, depending on the particular stability properties and merger parameters, violents events could drive a morphological loop in which the outcome could be a disc or a spheroid.