ABSTRACT

We discuss the results from a study in progress of radio–loud IRAS galaxies. We have discovered a class of gas-rich AGN which are characterized by large IR luminosities, and which are intermediate in radio luminosity, IR colour, and optical spectral class between the IRAS ultraluminous galaxies and powerful quasars. These objects form an important sample in studies of the AGN-starburst connection and may be the evolutionary link between the ultraluminous galaxies and quasars.

INTRODUCTION

The relationship between nuclear activity and galaxy evolution is poorly understood. Speculation on the subject ranges between ideas that Seyfert activity is due to nuclear starbursts, to the theory that the ultraluminous (LFIR ζ 1012 L⊙) far-infrared galaxies like Arp 220 are dust enshrouded, young quasars (Sanders et al. 1988). Unfortunately there exists no sample of active galaxies that can be used to test these various hypotheses since most samples used in these studies are selected either on the basis of optical emission-line equivalent width, or IRAS colour selection criteria, IRAS luminosity, etc. There is no ideal sample, but a good way of studying possible nuclear activity/evolution relationships is to select gas-rich galaxies with nuclear activity. We have selected sources from the IRAS survey (which is biased toward dusty, gas-rich objects) by using a completely independent indicator of galaxy activity: strong non-thermal radio emission. This sample of gas-rich radio galaxies also allows us to investigate the complex relationships between the ambient interstellar medium, the radio source, and the active nucleus.