Large Scale structure in the HI Parkes ALL-Sky Survey (HIPASS)

Abstract

We study the clustering properties of the recently compiled HIPASS neutral hydrogen (HI) sources catalogue using the two point correlation function in redshift space. If the two point correlation is modelled as a power law, $\xi(r)=(r_{0}/r)^{\gamma}$, then the best-fitting parameters for the HI selected galaxies are $r_{0}=4.3 \pm 0.3 h^{-1}$ Mpc with $\gamma=1.42 \pm 0.14$. Fixing the slope to its universal value $\gamma=1.8$, we obtain $r_{0}= 4.1^{+0.2}_{-0.3} h^{-1}$ Mpc. Comparing the measured two point correlation function with the predictions of the concordance cosmological model, we find that at the present epoch the HI selected galaxies are anti-biased with respect to the underline matter fluctuation field with bias value being $b_{0}\simeq 0.63$. Also, we investigate the evolution of the linear bias factor, $b(z)$, and we find to be a strongly dependent function of redshift. Finally, we estimate the HI selected galaxies redshift space distortion parameter $\beta \simeq \Omega_{\rm m}^{0.6}/b_{0}$ in order to correct the correlation function for the peculiar motions and we find $\beta\simeq 0.77$. Taking into account the corrections for the redshift space distortions the HI correlation length in real space is $r^{\rm re}_{0}=3^{+0.4}_{-0.3}h^{-1}$Mpc for $\gamma=1.42$ while using $\gamma=1.8$ we get $r^{\rm re}_{0}= 3.1 \pm 0.3 h^{-1}$Mpc.