THE CLUSTERING OF IRAS GALAXIES

We investigate the clustering of galaxies in the QDOT redshift survey of IPAS galaxies. We find that the two-point correlation function is well approximated by a power law of slope -1.11 +/- 0.09, with clustering length 3.87 +/- 0.32 h-1 Mpc(star) out to pair separations of approximately 25 h-1 Mpc. On scales larger than approximately 40 h-1 Mpc, the correlation function is consistent with zero. The rms fluctuation in the count of QDOT galaxies above the Poisson level in spheres of radius 8 h-1 Mpc is sigma8IRAS = 0.5 8 +/- 0.14, showing that fluctuations in the distribution of IRAS galaxies on these scales are smaller than those of optical galaxies by a factor of about 0.65, with an uncertainty of approximately 25 per cent. We find no detectable difference between the correlation functions measured in redshift space and in real space, leading to a 2sigma limit of b(IRAS)OMEGA0.6 > 1.05, where b(IRAS) is the bias factor for IRAS galaxies, and OMEGA is the cosmological density parameter. The QDOT autocorrelation function calculated in concentric shells increases significantly with shell radius. This difference is more likely to be due to sampling fluctuations than to an increase of the clustering strength with galaxy luminosity, but the two effects are difficult to disentangle; our data allow at most an increase of approximately 20 per cent in clustering strength for each decade in luminosity. For separations greater than approxiamately 3 h-1 Mpc, the cross-correlation function of Abell clusters (with richness R greater-than-or-equal-to 1) and QDOT galaxies is well approximated by a power law of slope -1.81 +/- 0.10, with clustering length 10.10 +/- 0.45 h-1 Mpc, and no significant signal beyond greater than or similar to 5 0 h-1 Mpc. This cross-correlation depends only weakly on cluster richness.