The IRAS 1 Jy Survey of Ultraluminous Infrared Galaxies. I. The Sample and Luminosity Function^*

A complete flux-limited sample of 118 ultraluminous infrared galaxies (ULIGs) has been identified from the IRAS Faint Source Catalog (FSC). The selection criteria were a 60 μm flux density greater than 1 Jy in a region of the sky δ > -40°, |b| > 30°. All sources were subsequently reprocessed using co-added IRAS maps in order to obtain the best available flux estimates in all four IRAS wavelength bands. The maximum observed infrared luminosity is L_ir = 10^12.90 L_☉, and the maximum redshift is z = 0.268. The luminosity function for ULIGs over the decade luminosity range L_ir = 10¹²-10¹³ L_☉ can be approximated by a power law Φ(L) ∝ L^-2.35[Mpc^-3 mag^-1]. In the local universe (z ≲ 0.1), the space density of ULIGs appears to be comparable to or slightly larger than that of optically selected QSOs at comparable bolometric luminosities. A maximum likelihood test suggests strong evolution for our sample; assuming density evolution proportional to (1 + z)^α we find α = 7.6 ± 3.2. Examination of the two-point correlation function shows a barely significant level of clustering, ξ(r) = 1.6 ± 1.2, on size scales r ~ 22 h^-1 Mpc.