First Results from the COLA Project- the Radio-FIR Correlation and Compact Radio Cores in Southern COLA Galaxies

Abstract

We present the first results from the COLA (Compact Objects in Low-power AGN) project which aims to determine the relationship between one facet of AGN activity, the compact radio core, with star formation in the circumnuclear region of the host galaxy. This will be accomplished by the comparison of the multi-wavelength properties of a sample of AGN with compact radio cores to those of a sample of AGN without compact cores and a matched sample of galaxies without AGN. In this paper we discuss the selection criteria for our galaxy samples and present the initial radio observations of the 107 Southern galaxies in our sample. Low-resolution ATCA observations at 4.8, 2.5 and 1.4 GHz and high resolution, single baseline snapshots at 2.3 GHz with the Australian LBA are presented. We find that for the majority of the galaxies in our sample, the radio luminosity is correlated with the FIR luminosity. Compact radio cores are detected in 9 galaxies. The majority (8/9) of these galaxies exhibit a significant radio excess and 50% (7/14) of the galaxies which lie above the radio-FIR correlation by more than 1 sigma have compact radio cores. The emission from the cores is too weak to account for this radio excess and there is no evidence that the radio luminosity of the compact cores is correlated with the FIR galaxy luminosity. The galaxies with compact cores tend to be classified optically as AGN, with two thirds (6/9) exhibiting Seyfert-like optical emission line ratios, and the remaining galaxies classified either as composite objects (2/9) or starburst (1/9). (Abridged)