The Clustering Properties of IRAS Galaxies

We investigate the clustering of galaxies in the QDOT redshift survey of IRAS galaxies. We find that the redshift space two-point correlation function is well approximated by a power-law of slope -1.11+\-0.09, with clustering length 3.87+\-0.32 Mpc/h out to pair separations of 25 Mpc\h. On scales larger than 40 Mpc/h, the correlation function is consistent with zero. The r.m.s. fluctuation in the count of QDOT galaxies above the Poisson level in spheres of radius 8 Mpc/h is \sigma_8^{IRAS}=0.58+\-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 25%. We find no detectable difference between the correlation functions measured in redshift space and in real space, leading to a $2\sigma$ limit of b_{IRAS}/\Omega^{0.6} >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 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 \sim 20% in clustering strength for each decade in luminosity. For separations greater than \sim 3 Mpc/h, the cross-correlation function of Abell clusters (with Richness R\ge 1) and QDOT galaxies is well approximated by a power-law of slope -1.81+\-0.10, with clustering length 10.10+\-0.45 Mpc/h, and no significant signal beyond \gsim 50 Mpc\h. This cross-correlation depends only weakly on cluster richness.