Evolution of dwarf early-type galaxies - I. Spatially resolved stellar populations and internal kinematics of Virgo cluster dE/dS0 galaxies

Abstract

Understanding the origin and evolution of dwarf early-type galaxies remains an important open issue in modem astrophysics. Internal kinematics of a galaxy contains signatures of violent phenomena which may have occurred, e.g. mergers or tidal interactions, while stellar population keeps a fossil record of the star formation history; therefore studying connection between them becomes crucial for understanding galaxy evolution. Here, in the first paper of the series, we present the data on spatially resolved stellar populations and internal kinematics for a large sample of dwarf elliptical (dE) and lenticular (dS0) galaxies in the Virgo cluster. We obtained radial velocities, velocity dispersions, stellar ages and metallicities out to 1-2 half-light radii by reanalysing already published long-slit and integral-field spectroscopic data sets using the NBURSTS full spectral fitting technique. Surprisingly, bright representatives of the dE/dS0 class (M B = -18.0 to -16.0 mag) look very similar to intermediate-mass and giant lenticulars and ellipticals: (1) their nuclear regions often harbour young metal-rich stellar populations always associated with the drops in the velocity dispersion profiles; (2) metallicity gradients in the main discs/spheroids vary significantly from nearly flat profiles to -0.9 dex r -1 e , i.e. somewhat three times steeper than for typical bulges; (3) kinematically decoupled cores were discovered in four galaxies, including two with very little, if any, large-scale rotation. These results suggest similarities in the evolutionary paths of dwarf and giant early-type galaxies and call for reconsidering the role of major mergers in the dE/dS0 evolution.