Iras Pscz V.s. Iras 1.2-jy Model Velocity Fields: a Spherical Harmonics Comparison

We have used the two IRAS redshift surveys, 1.2-Jy (Fisher et al. 1995) and PSCz (Saunders et al. 2000), tomodel the linear velocity fields within a redshift of 8 000 km s−1 and have compared them in redshift space. Thetwo 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 incomplete-ness of the PSCz catalog at fluxes ≤ 1.2 Jy. The 1.2-Jy and PSCz higher order velocity multipoles, particularlythe dipole and quadrupole components, appear to be consistent, suggesting that the dipole residuals found byDavis, Nusser and Willick (1996) when comparing 1.2-Jy and Mark III velocity fields probably originates fromthe Mark III velocities calibration procedure rather than from uncertainties in the model velocity field. Our resultsillustrate the efficiency of the spherical harmonics decomposition techniques in detecting possible differencesbetween real and model velocity fields. Similar analyses shall prove to be very useful in the future to test thereliability of next generation model velocity fields derived from new redshift catalogs like 2dFGRS (Colless etal. 2001), SDSS (York et al. 2000), 6dF and 2MRS. Subject headings: cosmology — theory – galaxies large-scale structure of the Universe — large-scale dynamics.