Radio Observations of the Hubble Deep Field South - a New Class of Radio-Luminous Galaxies?

Abstract

We present the first results from a series of radio observations of the Hubble Deep Field South and its flanking fields. Here we consider only those sources greater than 100 microJy at 20 cm, in an 8-arcmin square field that covers the WFPC field, the STIS and NICMOS field, and most of the HST flanking fields and complementary ground-based observations. We have detected 13 such radio sources, two of which are in the WFPC2 field itself. One of the sources in the WFPC field (source c) corresponds to a very faint galaxy, and several others outside the WFPC field can not be identified with sources in the other optical/IR wavebands. The radio and optical luminosities of these galaxies are inconsistent with either conventional starburst galaxies or with radio-loud galaxies. Instead, it appears that it belongs to a population of galaxies which are rare in the local Universe, possibly consisting of a radio-luminous active nucleus embedded in a very dusty starburst galaxy, and which are characterised by a very high radio/optical luminosity ratio.