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.

Many past attempts to kill MOND have only strengthened the theory. Better data on galaxy velocity curves clearly favor MOND (without fine-tuning) over cold dark matter. The usual critism on the incompleteness of classical MOND has spurred a Modified Relativity (MR) by Bekenstein. After outlining cosmology and lensing in MOND, we review MOND on small scales. We point out some potential problems of MOND in two-body relaxation and tidal truncation. We argue that the tidal field in any MOND-like gravity theory predicts that the Roche lobe sizes of a binary system are simply proportional to the binary baryonic mass ratio to the power 1/3. An immediate application of this result is that the tidal field and tidal truncation radii of million-star globular clusters and million-star dwarf galaxies (e.g., the Milky Way satellites NGC2419 and Carina) would be very similar because of the one-to-one relation between gravity and baryon distribution. This prediction appears, however, inconsistent with the fact that all globulars are truncated to much smaller sizes than all dwarf galaxies. Whether tide is uniquely determined by baryons can also be used to falsify any MOND-like gravity theory, whether classical or relativistic.

Dwarf galaxies are the most numerous type of galaxy in the local universe and are extremely important in the understanding of galaxy formation and evolution. A better understanding of the physics of dwarf galaxies is central to several current issues in observational cosmology. For example, simulations of galaxy evolution based on the Cold-Dark-Matter (CDM) model predict far more dwarfs than are observed locally. In the last 20 years there has been a huge amount of interest in the study of dwarf galaxies, partly due to these unanswered puzzles and also because of the improvements in the technology available.

We present preliminary results of a search for candidate dwarf galaxies in the NGC 3665 galaxy group. A $0.1 \times 0.1$ Mpc$^2$ field around the dominant early-type galaxy NGC 3665 was investigated using BRI images from the 2.5m INT WFC archive. A search with the SExtractor yielded 148 dwarf galaxy candidates in the range $-12 > M_B > -16$. The resulting luminosity function for the group can be described by a standard Schechter function.

We present semi-analytic models and Monte-Carlo simulations of QSO Ly$\alpha$ absorption line systems which originate in gaseous galactic halos, galaxy disks, and satellite halos around central galaxies. The relation between the properties of predicted absorption lines and those of galaxies has been investigated. Using a model with galactic halos, satellites, and HI disks of spirals, 60 % of the observed strong Ly$\alpha$ lines and all of the Lyman-limit systems can be predicted. The models predict $W_r \propto \rho^{-\alpha} L_B^{\beta} (1+z)^{-\gamma}$ with $\alpha \sim 0.5, \beta \sim 0.15, \gamma \sim 0.5$. For strong Ly$\alpha$ lines the average covering factor within $250 h^{-1} \kpc$ is $\sim 0.36$, with an average absorption radius of $\sim 150 h^{-1} \kpc$ for a galaxy halo, in good agreement with observations. Using mock imaging and spectroscopic surveys, selection effects are found to be able to strengthen the anti-correlation between line width and projected distance. The models were also applied to quasar metal absorption lines and more realistic absorption spectra with noise were simulated.

I present a large sample of precise ($\pm2$ km/s) stellar radial velocities obtained to serve as kinematic tracers in Milky Way dwarf spheroidal (dSph) satellite galaxies. This includes velocities for $\sim$750 member stars spanning several core radii in the Sculptor dSph, and $\sim$400 member stars extending out to the nominal tidal radius of the Fornax dSph. The resulting radial velocity dispersion profiles are flat, with no evidence for a sharp decrease in the velocity dispersion at large galactocentric radius in either Sculptor of Fornax. Application of a non-parametric method for estimating the radial mass distributions gives results consistent with mass determinations from classical analyses, with lower limits of $[M/L]_V \,{\sim} 7$ for Fornax and $[M/L]_V\,{\sim}4$ for Sculptor.

Thanks to the comprehensive sets of elemental abundances in eleven damped Ly$\alpha$ systems (DLAs) at $z_{\rm abs}=1.7-2.5$, we were able for the first time to study in detail the abundance patterns of a wide range of elements, the chemical variations in the interstellar medium, the star formation, and the age of galaxies outside the Local Group. Comparing the gas-phase abundance ratios of these high redshift galaxies, we found that they are very uniform, showing low RMS dispersions up to only 2–3 times higher than the statistical errors, for the majority of elements. The gas-phase abundance patterns of interstellar medium clouds within the DLA galaxies detected along the velocity profiles show on the other hand a high dispersion in several abundance ratios, indicating that variations in the gas phase, whatever their origin, are more confined to clouds within the DLA galaxies than to integrated profiles. The analysis of the cloud-to-cloud chemical variations within seven individual DLAs revealed that five of them show statistically significant variations, higher than 0.2 dex at more than 3 $\sigma$. The sources of these variations are both differential dust depletion and ionisation effects, however no evidence for variations due to different star formation histories was highlighted. These results place important constraints on scenarios of galaxy formation within the CDM hierarchical theory. The DLA abundance pattern comparison with chemical evolution models indicate that the DLAs may either be associated with the outer regions of spiral galaxies or with dwarf irregular galaxies both characterised by star formation histories with low star formation efficiencies. They may be very young galaxies with ages between 20–250 Myr, but also galaxies with ages longer than 1 Gyr. Their star formation rates per unit area are moderate, between $-3.2<\log {\rm SFR}<-1.4$ M$_{\odot}$ yr$^{-1}$ kpc$^{-2}$.

We present the results from a suite of N-body simulations of the tidal stripping of two-component dwarf galaxies comprising some stars and dark matter. We show that recent kinematic data from the local group dwarf spheroidal (dSph) galaxies suggests that dSph galaxies must be sufficiently massive ($10^9$–$10^{10}$M$_\odot$) that tidal stripping is of little importance for the stars. We discuss the implications of these massive dSph galaxies for cosmology and galaxy formation.

The current status and remaining questions of MgII absorbers are reviewed with an eye toward new results incorporating high quality Hubble Space Telescope images of the absorbing galaxies. In the end, we find that our current picture of extended gaseous regions around galaxies at earlier epochs is in need of some revision; MgII absorbing “halos” appear to be patchier and their geometry less regular than previously inferred. We also find that the so-called “weak” MgII absorbers are associated with normal galaxies over a wide range of impact parameters, suggesting that this class of absorber does not strictly select low surface brightness, dwarf galaxies, or IGM material. We emphasise the need for a complete survey of the galaxies in quasar fields, and the importance of obtaining rotation curves of confirmed absorbing galaxies.

We discuss the physical properties and the baryonic content of the Warm-Hot Intergalactic Medium (WHIM) at low redshifts. Cosmological simulations predict that the WHIM contains a large fraction of the baryons at $z=0$ in the form of highly-ionised gas at temperatures between $10^5$ and $10^7$ K. Using high-resolution ultraviolet spectra obtained with the Space Telescope Imaging Spectrograph (STIS) and the Far Ultraviolet Spectroscopic Explorer (FUSE) we have studied the WHIM at low redshifts by searching for intervening O VI and thermally broadened Lyman $\alpha$ (BLA) absorption toward a number of quasars and active galactic nuclei (AGNs). Our measurements imply cosmological mass densities of $\Omega_b$(O VI)$\geq0.0022 h_{75}^{-1}$ and $\Omega_{b}$(BLA)$\geq0.0035\,h_{75}^{-1}$. Our results suggest that the WHIM at low $z$ contains more baryonic mass than stars and gas in galaxies.

We report the results obtained from optical and near-infrared spectroscopy and also broad-band photometry of lensed low-luminosity galaxies ($1.3\leq z\leq 2.3$) located in the core of lensing clusters. The amplification factor allowed us to obtain the physical properties (SFR, abundance ratios, mass, age of the burst, dust contents, etc.) of star-forming galaxies, 1 to 2 magnitudes fainter than galaxies in a blank field, using the same indicators as in studies of low-redshift galaxies. A part of this study was concentrated on the dynamics of distant lensed galaxies using Integral Field Spectroscopy (SINFONI/VLT science verification programme).

We summarise recent results assessing the carbon and silicon abundances of the intergalactic medium (IGM) using the ‘pixel optical depth’ technique. We briefly discuss the implications of these results for models of intergalactic enrichment, focusing on distinguishing ‘early’ $z \gg 4$ enrichment by the first generations of stars and objects from ‘late’ enrichment by $2 \lesssim z\lesssim 5$ Ly-break galaxies. We then discuss the comparison of observed QSO spectra to simulated spectra generated from cosmological simulations that self-consistently include enrichment, and draw qualitative implications for the general picture of intergalactic enrichment at $z \gtrsim 2$.

One hundred early-type members of the Virgo Cluster have been observed with the Hubble Space Telescope (HST) as part of the ACS Virgo Cluster Survey. The survey and its extensions consists of F475W and F850LP imaging from the Advanced Camera for Surveys (ACS), supplemented by additional imaging and spectroscopy from WFPC2 HST, Chandra, Spitzer, Keck, KPNO, and CTIO. In this article, I report briefly on four scientific highlights from the program: (1) the discovery of a population of probable ultra-compact dwarf galaxies; (2) an improved measurement of the frequency of compact stellar nuclei in early-type galaxies; (3) a precise new measurement of Virgo's line-of-sight depth; and (4) new insights into the chemical evolution of galaxies from the color distributions of their globular cluster systems.