Velocity dispersion measurements of dwarf galaxies in the Coma cluster – implications for the structure of the fundamental plane

Abstract

We present intermediate-resolution spectroscopic data for a set of dwarf and giant galaxies in the Coma cluster, with −20.6 < M_R < −15.7. The photometric and kinematic properties of the brighter galaxies can be cast in terms of parameters which present little scatter with respect to a set of scaling relations known as the fundamental plane. To determine the form of these fundamental scaling relations at lower luminosities, we have measured velocity dispersions for a sample comprising 69 galaxies on the border of the dwarf and giant regime. Combining these data with our photometric survey, we find a tight correlation of luminosity and velocity dispersion, L ∝ σ^(2.0) , substantially flatter than the Faber–Jackson relation characterizing giant elliptical galaxies. In addition, the variation of mass-to-light (M/L) ratio with velocity dispersion is quite weak in our dwarf sample: M/L ∝ σ^(0.2). Our overall results are consistent with theoretical models invoking large-scale mass removal and subsequent structural readjustment, e.g. as a result of galactic winds.