The Environment of Local Ultraluminous Infrared Galaxies

Abstract

The spatial cluster-galaxy correlation amplitude, Bgc, is computed for a setof 76 (z < 0.3) ultraluminous infrared galaxies (ULIRGs) from the 1-Jy sample.The Bgc parameter is used to quantify the richness of the environment within0.5 Mpc of each ULIRG. We find that the environment of local ULIRGs is similarto that of the field with the possible exceptions of a few objects withenvironmental densities typical of clusters with Abell richness classes 0 and1. No obvious trends are seen with redshift, optical spectral type, infraredluminosity, or infrared color. We compare these results with those of localAGNs and QSOs at various redshifts. The 1-Jy ULIRGs show a broader range ofenvironments than local Seyferts, which are exclusively found in the field. Thedistribution of ULIRG Bgc-values overlaps considerably with that of local QSOs,consistent with the scenario where some QSOs go through a ultraluminousinfrared phase. However, a rigorous statistical analysis of the data indicatesthat these two samples are not drawn from the same parent population. The Bgcdistribution of QSOs shows a distinct tail at high Bgc-values which is notapparent among the ULIRGs. This difference is consistent with the fact thatsome of the QSOs used for this comparison have bigger and more luminous hoststhan the 1-Jy ULIRGs.