Infrared emission from compact groups of galaxies

Abstract

A search of the IRAS Point Source Catalog, Version 2 has revealed infrared sources within 1 arcmin of the optical centers of 54 gal axies in Hickson's catalog of compact groups of galaxies. The 60μm luminosity function for these galaxies has the same shape as the luminosity function of the IRAS bright galaxy sample. The space density of IRAS galaxies in compact groups is 60 times smaller than the space density of IRAS bright galaxies, indicating that of order 1% of all bright IRAS galaxies are in compact groups. The infrared emission from these galaxies is compared with the emission from samples of isolated galaxies by Keel et aI. and cluster galaxies studied by Bicay and Giovanelli . The fractional distribution of the ratio of far-infrared to optical luminosity of compact group galaxies is significantly larger than that of the isolated galaxies and comparable to that of the cluster galaxies. These results indicate that infrared emission is enhanced in the compact group galaxies, probably because of interactions. We also report an upper limit to the 2-10 keV X-ray flux of compact groups in our sample of 3χ 10⁴¹h^-2 ergs^-1, from the HEAO I A-2 experiment.