The PSCz dipole revisited

Abstract

We re-examine the gravitational acceleration (dipole) induced on the Local Group of galaxies by the Infrared Astronomical Satellite (IRAS) galaxy distribution of the Point Source Catalog redshift (PSCz) survey. We treat the cirrus-affected low galactic latitudes by utilizing a spherical harmonic expansion of the galaxy surface density field up to the octapole order. We find strong indications for significant contributions to the Local Group motion from depths up to ∼185 h-1 Mpc and a possible contribution even from ∼210 h-1 Mpc, in agreement with the recent analysis of Kocevski & Ebeling of a whole-sky X-ray cluster survey. What changes with respect to the previous PSCz dipole analyses is: (i) the large-scale dipole contributions and (ii) an increase of the overall dipole amplitude due to the important contribution of the local volume (≲4 h-1 Mpc), which we now take into account. This results in a lower value of the β (≈ Ωm0.6/b) parameter, which we find to be βIRAS ≃ 0.49 in real space. Therefore, for the concordance cosmological model (Ωm = 1 - ΩΛ = 0.3), the IRAS galaxies bias factor is bIRAS ≃1, which means that IRAS galaxies are good tracers of the underlying matter distribution. © 2006 RAS.