DISCOVERY AND ENVIRONMENT OF 5 ULTRALUMINOUS IRAS GALAXIES

Five ultraluminous IRAS galaxies have been discovered during the optic al identification of IRAS point sources in 313.9 deg(2) of the north g alactic cap. Results are presented of optical spectroscopic and imagin g observations of these galaxies, Three are classified as starburst or possibly starburst, and two are classified as Seyfert 2. The far-infr ared luminosities are in the range 1.3-3.1 x 10(12) L. (for H-0 = 50 k m s(-1) Mpc(-1)), with the two most luminous being the two Seyfert 2 g alaxies, Three of the five are clearly seen to be interacting or to ha ve very disturbed morphologies, presumably indicating interactions. No ne of the projected separations between galaxies is as low as the crit ical value of similar to 10 kPc suggested by Melnick and Mirabel for g alaxies to become ultraluminous, These separations are also not consis tent with the final mergers required by Mihos and Hernquist for ultral uminous starbursts, Closer but unobvious interactions are possible, ho wever, One interacting system has two components separated by similar to 8 kpc but it is not ultraluminous. In this case it may be that the galaxies lacked the dense, central bulges that would delay starbursts until the final merger.