IRAS galaxiesThe class of galaxies revealed by the IRAS satellite to be ultraluminous at far-infrared wavelengths. Most galaxies detected by IRAS are isolated disk galaxies whose infrared emission can be accounted for by normal star formation. IRAS galaxies have a bolometric luminosity as large as many quasars, and optical images show most of them to be strongly interacting pairs of spiral galaxies with exceptionally luminous nuclei. Their spectra indicate the presence of intense star formation, sometimes with the addition of an active nucleus, and show that the galaxies are rich in molecular gas. Such galaxies may well be the dust-shrouded predecessors of quasars that have been triggered with the intense starburst activity by the merger of the two spiral galaxies. The most extreme examples, with a far-infrared luminosity in excess of 1012 solar luminosities, are known as ultraluminous and hyperluminous IRAS galaxies.
Collins Dictionary of Astronomy © Market House Books Ltd, 2006