Spectroscopic studies of supergiant elliptical galaxies

Abstract

This investigation reports on detailed spectroscopic observations of four southern supergiant elliptical galaxies. A Fourier Difference method is derived to analyse absorption-line data to obtain velocities, velocity dispersions and line-strengths. The method is then applied to the galaxy sample to provide rotation curves and velocity dispersion profiles. A dynamical model is used to assist interpretation, in which a normal elliptical galaxy is placed in a massive background of dark material. The observations indicate that supergiant elliptical galaxies do not rotate; are over-luminous for their central velocity dispersions and have velocity dispersion profiles which depend on the location of the galaxy within the cluster. Modelling of the profiles suggests that any dark background has a density scale length less than or equal to the cluster galaxies themselves. Two dumb-bell galaxies included in the sample are probably merging. The conclusion of this work is that the formation of supergiant elliptical galaxies is primarily an evolutionary process [eg galactic cannibalism], but does depend on certain initial conditions which affect the way in which that evolution proceeds [eg tidal stripping].