The IRAS PSCz Dipole

We use the PSCz IRAS galaxy redshift survey to analyze the cosmological galaxy dipole out to a distance 300 h Mpc. The masked area is filled in three different ways, firstly by sampling the whole sky at random, secondly by using neighbouring areas to fill a masked region, and thirdly using a spherical harmonic analysis. The method of treatment of the mask is found to have a significant effect on the final calculated dipole. The conversion from redshift space to real space is accomplished by using an analytical model of the cluster and void distribution, based on 88 nearby groups, 854 clusters and 163 voids, with some of the clusters and all of the voids found from the PSCz database. The dipole for the whole PSCz sample appears to have converged within a distance of 200 hMpc and yields a value for β = Ω/b = 0.75 (+0.11,-0.08), consistent with earlier determinations from IRAS samples by a variety of methods. For b = 1, the 2− σ range for Ωo is 0.43-1.02. The direction of the dipole is within 13o of the CMB dipole, the main uncertainty in direction being associated with the masked area behind the Galactic plane. The improbability that further major contributions to the dipole amplitude will come from volumes larger than those surveyed here means that the question of the origin of the CMB dipole is essentially resolved.