The FIRST Sample of Ultraluminous Infrared Galaxies at High Redshift. I. Sample and Near-Infrared Morphologies

We present a new sample of distant ultraluminous infrared galaxies. The sample was selected from a positional cross-correlation of the IRAS Faint Source Catalog with the FIRST database. Objects from this set were selected for spectroscopy by virtue of following the well-known star-forming galaxy correlation between 1.4 GHz and 60 μm flux, and by being optically faint on the POSS. Optical identification and spectroscopy were obtained for 108 targets at the Lick Observatory 3 m telescope. Most objects show spectra typical of starburst galaxies and do not show the high-ionization lines of active galactic nuclei. The redshift distribution covers 0.1 < z < 0.9, with 13 objects at z > 0.5 and an average redshift of = 0.31. K-band images were obtained at the IRTF, Lick, and Keck observatories in sub-arcsec seeing of all optically identified targets. About two-thirds of the objects appear to be interacting galaxies, while the other one-third appear to be normal. Nearly all the identified objects have far-IR luminosities greater than 1011 L⊙, and ∼25% have LFIR > 1012 L⊙.