IAU Symposium Abstract S186-095T

Ultraluminous Infrared Galaxies

D. B. Sanders
Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI < sanders@ifa.hawaii.edu >

Ground-based and satellite observations of Ultraluminous Infrared Galaxies (ULIGs: Lir > 1012 Lsun) show clearly that most if not all ( > 90%) of these objects are advanced mergers of gas-rich spirals (typically 0.5-2 L*) of roughly comparable mass. In the local Universe z < 0.5), the space density of ULIGs is approximately 1.5-2 times larger than that of optically selected QSOs. There is also evidence for strong evolution in the population of ULIGs over the redshift range z=0.1-0.35. Assuming pure density evolution of the form (1 + z)a, a=7.2 +/- 2.5.