Ultraluminous infrared galaxies and the origin of quasars

An evolutionary connection between ultraluminous infrared galaxies and quasars is deduced from observations of all 10 infrared galaxies with luminosities L(8-1000 microns) of 10 to the 12th solar luminosities and greater. The observations show that all the galaxies are strongly interacting, with most appearing to be advanced mergers of two spiral disks. Nine of the 10 have dominant nonthermal optical emission lines, and the near-infrared colors show a mixture of starburst and AGN energy sources. All appear to be extremely rich in molecular gas. These observations are interpreted to imply that the ultraluminous infrared objects are dust-enshrouded quasars. A model is presented for the formation of ultraluminous infrared galaxies through the strong interaction or merger of two molecular gas-rich spirals. 76 references.