IRAS PSCz v.s. 1.2-Jy Velocity and Density Fields: A Spherical Harmonics Comparison

Abstract

We have used the two IRAS redshift surveys, 1.2-Jy (Fisher et al 1995) and PSCz (Saunders et al 2000), to model the linear velocity fields within a redshift of 8,000 km/s and have compared them in redshift space. The two velocity fields only differ significantly in their monopole components. The monopole discrepancy cannot be solely ascribed to shot-noise errors and incomplete sky coverage. The mismatch seems to arise from incompleteness of the PSCz catalog at fluxes $\le$ 1.2 Jy. The 1.2-Jy and PSCz higher order velocity multipoles, particularly the dipole and quadrupole components, appear to be consistent, suggesting that the dipole residuals found by Davis, Nusser and Willick (1996) when comparing 1.2-Jy and MarkIII velocity fields probably originates from the MarkIII velocities calibration procedure rather than from uncertainties in the model velocity field. Our results illustrate the efficiency of the spherical harmonics decomposition techniques in detecting possible differences between real and model velocity fields. Similar analyses shall prove to be very useful in the future to test the reliability of next generation model velocity fields derived from new redshift catalogs like 2dFGRS (Colless et al 2001), SDSS (York et al 2000), 6dF and 2MRS.