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 Catalogue redshift survey (PSCz). 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 $\sim 185$ $h^{-1}$ Mpc and possible contribution even from $\sim 210$ $h^{-1}$ 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: (a) the large-scale dipole contributions and (b) an increase of the overall dipole amplitude due to the important contribution of the local volume ($\mincir 4 h^{-1}$Mpc), which we now take into account. This results in a lower value of the $β(\equiv Ω_{\rm m}^{0.6}/b)$ parameter, which we find to be $β_{\rm IRAS} \simeq 0.49$ in real space. Therefore, for the concordance cosmological model ($Ω_{\rm m}=1-Ω_Λ=0.3$) the IRAS galaxies bias factor is $b_{\rm IRAS}\simeq 1$ which means that IRAS galaxies are good traces of the underlying matter distribution.