A cold dark matter halo big enough to host the Milky Way contains hundreds of subhalos massive enough to host dwarf galaxies. The difference to the much smaller observed number of satellite galaxies seems to be a problem for CDM. The galaxy number density profile and disk like configuration are also different form the total subhalo populations in CDM simulations. A number of different models of dwarf galaxy formation which are able to reproduce the right number of luminous subhalos have been proposed. Some of them also give the right radial distributions and make disk like configurations more probable. Additional information about the typical formation times and sites of dwarf galaxies can be found in the stellar halo of the Milky Way, i.e. from the stellar debris of tidally disrupted dwarfs. A stellar halo with a realistic concentration is obtained when most dwarfs form early (before redshift 10) in small halos (virial mass above $10^8$ solar masses). This mass scale found from simulations of dark matter structure formation coincides with the virial temperature of $10^4 K$ which is needed for efficient atomic cooling.

We study the physical conditions in damped Lyman-$\alpha$ systems (DLAs), using a sample of 33 systems toward 26 QSOs acquired for a recently completed survey of H$_2$ by Ledoux et al. (2003). H$_2$ is detected in 13-20% of the DLAs in our sample. Using the rotation level populations of H$_2$ and fine-structure excitations of C I we show the mean kinetic temperature of H$_2$ components is 153$\pm$78 K, $n_{\rm H}$ = 10$-$250 cm$^{-3}$, and the ambient radiation field is similar to or slightly higher than the mean diffuse UV field of the Galaxy. Combining this with the success rate of detecting H$_2$ in DLAs we conclude that at least 13$-$20% of DLAs at $z_{\rm abs}\ge1.9$ show the presence of CNM and substantial star-formation activity. C II$^*$ absorption is detected in all the components where H$_2$ absorption is seen. The level populations of C II in these systems is consistent with the physical parameters derived from the excitation of H$_2$ and C I. We detect C II$^*$ in about 50% of the DLAs and therefore in a considerable fraction of DLAs that do not show H$_2$. The absence of C I absorption, the measured N(C II$^*$)/N(C II) and N(Al III)/N(Al II) ratios in these systems are consistent with the gas having lower density (n$_{\rm H} = 0.3-6 cm^{-3}$) than that seen in the H$_2$ components. 50% of the DLAs that do not show C II$^*$ are consistent with them originating from a low density warm neutral medium.

We present results from two projects in which we have used the HI 21cm emission line as a tracer of gas-rich galaxy populations in the vicinity of Lyman-$\alpha$ absorbers. In the first case, we examine the HI environment of SBS 1543+593, the nearest damped Lyman-$\alpha$ absorber. We use a VLA map of the region around this LSB galaxy which itself shows an extended HI disk to identify 3 gas-rich neighbours within 185 kpc. While it is not clear whether we should expect local damped Lyman-$\alpha$ systems to reside in such gas-rich regions, we would expect this kind of environment to be more prevalent at higher redshifts where less of the gas is in the dense inner regions of galaxies or has been consumed by star formation. This local galaxy is the only system in which we can study the gaseous environment in this kind of detail. In the second case, we examine the HI environment surrounding 16 Lyman-$\alpha$ forest absorbers along 4 QSO sight-lines. We do not detect any gas-rich galaxies at the absorber positions indicating that, at least down to our sensitivity limits, these absorption lines do not seem to be associated with galaxy halos. For half of the Lyman-$\alpha$ absorption systems there is a galaxy within 500 kpc, but for the other half there is not. In two cases there is no galaxy within 2 Mpc of the Lyman-$\alpha$ absorption systems indicating that absorbers do, in some cases, reside in voids.

We present new Keck/HIRES observations of seven of the highest-redshift known quasars. These include four with $z_{\rm qso}\ge 5.8$ and two with $z_{\rm qso}\ge 6.3$. The data will be used to produced a complete statistical description of the Ly$\alpha$ forest at $z > 5$, allowing us to better assess the significance of the strong absorption seen at $z>6.2$. We introduce the statistics of transmission gaps as a means of characterising the high-redshift evolution of the forest. In addition, we identify several clear absorption lines of low optical depth in the quasar proximity regions and briefly discuss using these to place constraints on the thermal history of the IGM at $z>5$.

We are conducting a survey of 44 early-type galaxies in the Fornax Cluster using the Advanced Camera for Surveys on the Hubble Space Telecope: the ACS Fornax Cluster Survey. We briefly describe the survey, the selection of the target galaxies and some of the scientific objectives.

The recent development of large, complete samples which identify high-redshift galaxies at $z\sim5.7$ and $z\sim 6.5$ from deep, wide-field surveys provides detailed information on the earliest galaxies, their numbers, spatial and kinematic distributions, and implications for early reionisation of the IGM. In this contribution we present results of spectroscopic studies of $z\sim 5.7$ and $z\sim6.5$ galaxies identified from our deep, Lyman alpha narrow-band and multicolour surveys conducted with the SuprimeCam mosaic CCD camera on the 8.3-m Subaru telescope and observed with the DEIMOS multi-object spectrograph on Keck. The luminosity function of the $z\sim6.5$ galaxies is shown to be similar to the luminosity function of the $z\sim 5.7$ galaxy samples, suggesting that a substantial star-forming population is already in place at $z\sim 6.5$. Comparisons of both individual and stacked spectra of galaxies in these two samples show that the Lyman alpha emission profiles, equivalent widths, and continuum break strengths do not substantially change over this redshift interval. The wide-field nature of the surveys also permits mapping of the large-scale distribution of high-redshift galaxies in spatial structures extending across individual SuprimeCam fields ($\sim 60$ Mpc). Field-to-field variations in the number of objects at $z\sim 6.5$ may shortly be able to place constraints on the porosity of the reionisation boundary.

We investigate the evolution of damped Ly$\alpha$ absorption systems (DLA) from hierarchical structure formation models by exploring the basic properties of DLA host-galaxies (DLA galaxies) to clarify the connection between DLAs and galaxies. We find that DLA galaxies primarily consist of low surface brightness dwarf galaxies. For example, at redshift $z \le 1$, DLA galaxies have typical radius 3 kpc, surface brightness 22–27 mag arc-sec$^{-2}$, and star formation rate $10^{-2}$ M$_{\odot}$/yr. We discuss selection effects in the detection in emission caused by compactness and brightness. Finally, we explore the radio properties at $z=0$ by comparing the observational results from blind radio surveys.

We present results of a photometric survey for carbon stars in the M31 dwarf spheroidal galaxies. From the low frequency of carbon stars in these galaxies compared to their Milky Way cousins we conclude that they consist of predominantly ancient stellar populations. However, the complexity and variety of the metallicity distributions in the M31 dwarf spheroidals suggest that they still experienced an extended epoch of star formation.

In recent years there has been rapid progress in the research of Active Galactic Nuclei (AGNs), such as central super-massive black holes (SBH), accretion processes, and their host galaxies. Using data from ROSAT point sources, we found that the soft X-ray spectra of narrow-line Seyfert 1 galaxies (NLS1s) and Blazars become harder during X-ray flux increases, while the spectra of broad-line AGNs (BL AGNs) become softer. From ASCA data, we found that NLS1s and BL AGNs follow the same $\sigma^{2}-M_{MBH}$ relation, where $\sigma^{2}$ is the excess variance in the hard X-ray band. With the accretion efficiency of AGNs, we found that most of the radio-loud quasars possibly possess a Kerr SBH, while the Seyfert 1 galaxies and radio-quiet quasars possess Schwarzschild SBH. We also studied the relation between the central black holes and their host galaxies. It was found that NLS1s appear to have genuinely lower MBH/bulge mass ratios. And the width of the [O III] line is not a good tracer of host velocity dispersion. NLS1s play a special role in our understanding of the evolution of galaxies and their central SBHs.

In this contribution initial results are presented from a program to study in detail the stellar populations of dwarf Spheriodal (dSph) galaxies in three nearby groups. The long-term aim of the program is to assess the influence of environment in governing the evolution of these low-luminosity systems. Specific results described here include the detection and measurement of intermediate-age upper-AGB populations in dSphs in the M81 and Cen A groups, and the discovery that four of the five low-luminosity early-type dwarfs in the low density Sculptor group contain modest amounts of neutral hydrogen gas.

We obtained velocity dispersion and line strength index measurements for 69 faint early–type galaxies in the core of the Coma cluster. The full sample spanning $-22.0 < M_R < -17.5$ mag includes 36 dE/dS0 galaxies. We examine the $L$–$\sigma$ relation and compare it to that of bright ellipticals from the literature. The slope defined by the faint early–type galaxies including dEs/dS0s is significantly shallower, $L \propto \sigma^{2.01\pm0.36}$, than that defined by luminous elliptical galaxies, $L \propto \sigma^{4}$. Moreover, there is no evidence for a change of slope at the typical division between dwarfs and ordinary elliptical galaxies at $M_B=-18$ mag; rather, the change in slope appears at $M_B=-20.5$ mag. We show that rotation in the fainter galaxies cannot be solely responsible for the change of slope in the $L$–$\sigma$ relation. We also plot metallicity and age-dependent line strength indices in diagnostic diagrams and find that our galaxies span a wide range in both age and metallicity.

The growing number of observational details questions the standard picture of the evolution of dwarf ellipticals and argues for a complex evolution dominateded by environmental effects. Here we compile some standard and most recent observational issues and discuss the results of simple models in comparison with observations. The necessity of further model developments are justified and prospected.

Dwarf galaxies are at the center of a long debated galaxy evolution puzzle.In the Local Group, there seems to be evidence that the exact morphology of a dwarf is strongly correlated with its environment: late-types (dwarf irregulars, dIrr) are further away from major group members than early-types (dwarf ellipticals and dwarf spheroidals, dE). In general, the early-types, with their smooth ellipsoid light distribution, have no detected interstellar medium (ISM), possess low angular momentum and have low current star formation rates. The late-types have an irregular appearance, large quantities of neutral hydrogen (HI), ongoing star formation and higher angular momentum.

M32 and other compact dwarf galaxies present interesting evolutionary puzzles. Why are most dwarf galaxies low density systems while a very few, like M32, have the highest stellar densities of any galaxies? We suggest that gas capture should be added to the tidal stirring mix as a way to make high density M32-type dwarfs starting with relatively ordinary satellite galaxies. This paper presents some of the basic features and issue associated with gas capture models.

To date, half a dozen DLAs have been detected in GRB afterglows, but most have modest signal-to-noise ratios. Our detection of a DLA in the afterglow of GRB 030323 is unambiguous: its neutral hydrogen column density is log N(HI)=21.90$\pm$0.07, higher than any (GRB- or QSO-) DLA HI column density inferred directly from Ly$\alpha$ in absorption. We discuss several other properties such as the metallicity, the detection of fine-structure lines of SiII, and our strong upper limit on the H$_2$ content. The GRB afterglow allows us to infer all these quantities, even with the host being as faint as V=28. The successful launch of the Swift satellite (November 2004) has made high-resolution spectroscopy of a large sample of GRB afterglows possible. This will offer a unique way to study in detail the interstellar medium inside GRB host galaxies as a function of redshift.

We present a new technique to determine age and metallicity of old stellar populations (globular clusters and elliptical galaxies) using an iterative principal component analysis on narrow band (Strömgren) colors. Our technique is capable of reproducing globular cluster [Fe/H] values to 0.02 dex and CMD ages to 1.0 Gyrs. We also present preliminary results on the application of our technique to a sample of high mass, field ellipticals and low mass, cluster dwarf ellipticals. We confirm the results of earlier studies which find that globular clusters increase in metallicity with age and that age and metallicity increase with galaxy mass. However, we find that dwarf ellipticals deviate from the elliptical sequence by having little to no correlation between age and metallicity.

We present the results of optical stellar rotation curves of 16 dwarf elliptical galaxies in the Virgo Cluster. Approximately half of this sample have significant velocity gradients along their optical major axis, with typical rotation amplitudes of 20—30 km s$^{-1}$. Evidence for a relationship between the rotation amplitude and galaxy luminosity is found and agrees well with the Tully-Fisher relation. The similarity in the scaling relations of dIs and dEs implies that it is unlikely that dEs evolve from significantly more luminous galaxies. These observations reaffirm the possibility that some cluster dwarf elliptical galaxies may be formed when the neutral gaseous medium is stripped from dwarf irregular galaxies in the cluster environment.

The Local Group offers an excellent laboratory for near-field cosmology by permitting us to use the resolved stellar content of its constituent galaxies as probes of galaxy formation and evolution, which in turn is an important means for testing cosmological models of hierarchical structure formation. In this review, we discuss the the least massive, yet most numerous type of galaxy in the Local Group, the dwarf spheroidal galaxies, and compare their properties to cosmological predictions. In particular, we point out problems found with a simple building block scenario and with effects expected from reionization. We show that the star formation histories of dSphs are inconsistent with the predicted cessation of star formation after reionization; instead, extended star formation episodes are observed. The Galactic dSphs contain in part prominent intermediate-age populations, whereas the Galactic halo does not. Conversely, the M31 dSphs are almost entirely old, while the M31 halo contains a substantial intermediate-age population. These differences in the population structure as well as the differences in the modes of star formation inferred from [α/Fe] ratios make dSphs unlikely major contributors to the build-up of the Galactic and M31 halo unless most of the accretion occurred at early epochs. On the other hand, there is clear evidence for ongoing harassment and accretion of a number of dSphs.

We present a model which allows for a self-consistent calculation of spectrophotometric, chemical, and dust evolution of spiral and irregular galaxies. Dust evolution is treated without the Instantaneous Recycling Approximation on the basis of the Dwek (1998) model, where up-to-date dust yields for SNe and intermediate mass stars on their AGB phase are taken into account. Confronting model results with the chemical abundances observed in DLA systems, we conclude that spiral and irregular galaxies are good candidates for DLAs.

This contribution describes a recent photometric survey of the Fornax dwarf spheroidal galaxy. CCD photometry in two colours (V and I) was obtained for a 10 degree$^2$ region centred on Fornax. By selecting stars sharing the colour-magnitude space of this system's RGB, we were able to remove the majority of field stars, and thereby probe the structure of Fornax at a previously unattained level. The data indicate that this dwarf galaxy contains two shells, both aligned with the Fornax major axis. Also, two ‘lobed’ structures sharing the alignment of these shells were discovered beyond the nominal tidal radius. These structures appear to be the remnant of a companion dwarf galaxy which merged with Fornax approximately 2 Gyr ago.