Radio-excess infrared galaxies: a new population of active galaxies?

Abstract

We present a sample of active galaxy candidates, found by comparing the IRAS catalogue with the Parkes-MIT-NRAO southern 6.3-cm radio survey. We select galaxies that depart from the radio versus far-infrared (FIR) relation displayed by normal galaxies, to produce a sample of 12 candidate radio-excess, gas-rich, active galaxies. Such objects have been discussed recently with the aim of understanding how they relate to more familiar types of active galactic nuclei (AGN). Do they represent a different evolutionary stage of radio-quiet AGN, or are they a familiar type of AGN but in an unusual environment, perhaps dust-enshrouded quasars or their progenitors? The pilot sample presented here is intended to find a usefully large number of radio-excess AGN suitable for further study, and to test the efficiency of the selection criteria. We give radio and FIR data for the sample, along with optical identifications, spectroscopic classifications, and redshifts from the literature. These data reveal some unusual and interesting objects, despite the relatively small area covered by this initial survey.