Introduction

Early-type galaxies constitute quite a heterogeneous group of galaxies. Many of the properties of these systems vary from galaxy to galaxy and, more interestingly, vary systematically with luminosity and environment. Many of the differences may be related to the amount of gas (and dissipation) present during the formation and the evolution of the galaxies. Moreover, evidence is accumulating now that some early-type galaxies probably have a long-lived interstellar medium (ISM; e.g. Knapp 1998). To help understand the mechanisms and processes behind the differences between different early-type galaxies and to study the ISM observed in some of these galaxies, it may be worthwhile to study the systematics of the properties of the neutral hydrogen in early-type galaxies as function of luminosity and environment. To this end, we have observed a large number of early-type galaxies with the Australia Telescope Compact Array and the Very Large Array (Morganti et al. 1997a,b, 1998a,b). In particular, we have tried to observe galaxies over a range of luminosities in order to see whether the HI properties of low-luminosity early-type galaxies (which we define here as galaxies with absolute blue magnitude in the range of -16 to -19) vary systematically with luminosity. Here we give a brief overview of the results obtained so far. In section 2 we give a brief overview of properties of early-type galaxies observed at other wavebands that are relevant for the discussion. In section 3 we briefly discuss the HI content of early-type galaxies and in section 4 we summarize the morphology and the kinematics of the HI as function of luminosity and environment and the relation of these properties to other properties of the galaxies.

© Copyright Astronomical Society of Australia 1997