Annu. Rev. Astron. Astrophys. 1996. 34: 749-792
Copyright © 1996 by Annual Reviews Inc. All rights reserved

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LUMINOUS INFRARED GALAXIES

D. B. Sanders

Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822

I. F. Mirabel

Service d'Astrophysique, Centre d'Etudes de Saclay, 91191 Gif sur Yvette, France

KEY WORDS: luminosity function, starbursts, active galactic nuclei, molecular gas, dust emission

ABSTRACT. At luminosities above 10¹¹ L, infrared galaxies become the dominant population of extragalactic objects in the local Universe (z ltapprox 0.3), being more numerous than optically selected starburst and Seyfert galaxies and quasi-stellar objects at comparable bolometric luminosity. The trigger for the intense infrared emission appears to be the strong interaction/merger of molecular gas-rich spirals, and the bulk of the infrared luminosity for all but the most luminous objects is due to dust heating from an intense starburst within giant molecular clouds. At the highest luminosities (L_ir > 10¹² L), nearly all objects appear to be advanced mergers powered by a mixture of circumnuclear starburst and active galactic nucleus energy sources, both of which are fueled by an enormous concentration of molecular gas that has been funneled into the merger nucleus. These ultraluminous infrared galaxies may represent an important stage in the formation of quasi-stellar objects and powerful radio galaxies. They may also represent a primary stage in the formation of elliptical galaxy cores, the formation of globular clusters, and the metal enrichment of the intergalactic medium.