We present optical VLT spectroscopy of 16 dwarf elliptical galaxies (or dEs) comparable in mass to NGC 205, and belonging to the Fornax cluster and to nearby groups of galaxies. Using full-spectrum fitting, we derive radial profiles of the SSP-equivalent ages and metallicities. We make a detailed analysis with ulyss and steckmap of the star-formation history in the core of the galaxies and in an aperture of one effective radius. We resolved the history into 1 to 4 epochs. The statistical significance of these reconstructions were carefuly tested; the two programs give remarkably consistent results.The old stellar population of the dEs, which dominates their mass, is likely coeval with that of massive ellipticals or bulges, but the star formation efficiency is lower. Important intermediate age (1-5 Gyr) populations, and frequently tails of star formation until recent times are detected. These histories are reminiscent of their lower mass dSph counterparts of the Local Group.Most galaxies (10/16) show significant metallicity gradients, with metallicity declining by 0.5 dex over one half-light radius on average. These gradients are already present in the old population. The flattened (or discy), rotating objects (6/16) have flat metallicity profiles. This may be consistent with a distinct origin for these galaxies or it may be due to their geometry. The central SSP-equivalent age varies between 1 and 6 Gyr, with the age slowly increasing with radius in the vast majority of objects. The group and cluster galaxies have similar radial gradients and star-formation histories.The strong and old metallicity gradients place important constraints on the possible formation scenarios of dEs. Numerical simulations of the formation of spherical low-mass galaxies reproduce these gradients, but they require a longer time for them to build up. A gentle depletion of the gas, by ram-pressure stripping or starvation, could drive the gas-rich, star-forming progenitors to the present dEs.

We test four commonly used astrophysical simulation codes, enzo, flash, gadget and hydra, using a suite of numerical problems with analytic initial and final states. Situations similar to the conditions of these tests, a Sod shock, a Sedov blast, and both a static and translating King sphere, occur commonly in astrophysics, where the accurate treatment of shocks, sound waves, supernovae explosions and collapsed haloes is a key condition for obtaining reliable validated simulations. We demonstrate that comparable results can be obtained for Lagrangian and Eulerian codes by requiring that approximately one particle exists per grid cell in the region of interest. We conclude that adaptive Eulerian codes, with their ability to place refinements in regions of rapidly changing density, are well suited to problems where physical processes are related to such changes. Lagrangian methods, on the other hand, are well suited to problems where large density contrasts occur and the physics are related to the local density itself rather than the local density gradient.

Dwarf galaxies, as the most numerous type of galaxy, offer the potential to study galaxy formation and evolution in detail in the nearby universe. Although they seem to be simple systems at first view, they remain poorly understood. In an attempt to alleviate this situation, the MAGPOP EU Research and Training Network embarked on a study of dwarf galaxies named MAGPOP‐ITP. In this paper, we present the analysis of a sample of 24 dwarf elliptical galaxies (dEs) in the Virgo cluster and in the field, using optical long‐slit spectroscopy. We examine their stellar populations in combination with their light distribution and environment. We confirm and strengthen previous results that dEs are, on average, younger and more metal‐poor than normal elliptical galaxies, and that their [α/Fe] abundance ratios scatter around solar. This is in accordance with the downsizing picture of galaxy formation where mass is the main driver for the star formation history. We also find new correlations between the luminosity‐weighted mean age, the large‐scale asymmetry, and the projected Virgocentric distance. We find that environment plays an important role in the termination of the star formation activity by ram‐pressure stripping of the gas in short time‐scales, and in the transformation of discy dwarfs to more spheroidal objects by harassment over longer time‐scales. This points towards a continuing infalling scenario for the evolution of dEs.

Abstract. This paper is the first in a series in which we present the results of an ESO Large Program on the kinematics and internal dynamics of dwarf elliptical galaxies (dEs). We obtained deep major and minor axis spectra of 15 dEs and broad-band imaging of 22 dEs. Here, we investigate the relations between the parameters that quantify the structure (B-band luminosity L B , half-light radius R e , and mean surface brightness within the half-light radius I e = L B /2πR 2 e ) and internal dynamics (velocity dispersion σ) of dEs. We confront predictions of the currently popular theories for dE formation and evolution with the observed position of dEs in log L B vs. log σ, log L B vs. log R e , log L B vs. log I e , and log R e vs. log I e diagrams and in the (log σ, log R e , log I e ) parameter space in which bright and intermediate-luminosity elliptical galaxies and bulges of spirals define a Fundamental Plane (FP). In order to achieve statistical significance and to cover a parameter interval that is large enough for reliable inferences to be made, we merge the data set presented in this paper with two other recently published, equally large data sets. We show that the dE sequences in the various univariate diagrams are disjunct from those traced by bright and intermediateluminosity elliptical galaxies and bulges of spirals. It appears that semi-analytical models (SAMs) that incorporate quiescent star formation with an essentially z-independent star-formation efficiency, combined with post-merger starbursts and the dynamical response after supernova-driven gas-loss, are able to reproduce the position of the dEs in the various univariate diagrams. SAMs with star-formation efficiencies that rise as a function of redshift are excluded since they leave the observed sequences traced by dEs virtually unpopulated. dEs tend to lie above the FP and the FP residual declines as a function of luminosity. Again, models that take into account the response after supernova-driven mass-loss correctly predict the position of dEs in the (log σ, log R e , log I e ) parameter space as well as the trend of the FP residual as a function of luminosity. While these findings are clearly a success for the hierarchical-merging picture of galaxy formation, they do not necessarily invalidate the alternative "harassment" scenario, which posits that dEs stem from perturbed and stripped late-type disk galaxies that entered clusters and groups of galaxies about 5 Gyr ago.

We present deep single-dish H i observations of a sample of six nearby E+A galaxies (0:05 < z < 0:1). A nonnegligible fraction of a local sample of E+As are detected in H i. In four galaxies, we have detected up to a few times 10 9 M of neutral gas. These E+A galaxies are almost as gas-rich as spiral galaxies with comparable luminosities. There appears to exist no direct correlation between the amount of H i present in an E+A galaxy and its star formation rate as traced by radio continuum emission. Moreover, the end of the starburst does not necessarily require the complete exhaustion of the neutral gas reservoir. Most likely, an intense burst of star formation consumed the dense molecular clouds, which are the sites of massive star formation. This effectively stops star formation, even though copious amounts of diffuse neutral gas remain. The remaining H i reservoir may eventually lead to further episodes of star formation. This may indicate that some E+As are observed in the inactive phase of the star formation duty cycle.