Large-scale structure in the HI Parkes All-Sky Survey:filling the voids with HI galaxies?

We estimate the two-point correlation function in redshift space of the recently compiled HI Parkes All-Sky Survey neutral hydrogen (HI) sources catalogue, which if modelled as a power law, xi(r) = (r(0)/r)(gamma), the best-fitting parameters for the HI selected galaxies are found to be r(0) = 3.3 +/- 0.3 h(-1) Mpc with gamma = 1.38 +/- 0.24. Fixing the slope to its universal value gamma = 1.8, we obtain r(0) = 3.2 +/- 0.2 h(-1) Mpc.Comparing the measured two-point correlation function with the predictions of the concordance cosmological model (Omega(Lambda) = 0.74), we find that at the present epoch the HI selected galaxies are antibiased with respect to the underlying matter fluctuation field with their bias value being b(0) similar or equal to 0.68. Furthermore, dividing the HI galaxies into two richness subsamples we find that the low-mass HI galaxies have a very low present bias factor (b(0) similar or equal to 0.48), while the high-mass HI galaxies trace the underlying matter distribution as the optical galaxies (b(0) similar or equal to 1). Using our derived present-day HI galaxy bias we estimate their redshift-space distortion parameter, and correct accordingly the correlation function for peculiar motions. The resulting real-space correlation length is r(0)(re) = 1.8 +/- 0.2 h(-1) Mpc r(0)(re) = 3.9 +/- 0.6 h(-1) Mpc for the low- and high-mass HI galaxies, respectively. The low-mass HI galaxies appear to have the lowest correlation length among all extragalactic populations studied to date. In order to corroborate these results we have correlated the IRAS-Point Source Catalogue for Redshift (PSCz) reconstructed density field, smoothed over scales of 5 h(-1) Mpc, with the positions of the HI galaxies, to find that indeed the HI galaxies are typically found in negative overdensity regions (delta rho/rho(PSCz) less than or similar to 0), even more so the low-mass HI galaxies.Finally, we also study the redshift evolution of the HI galaxy linear bias factor and find that the HI-galaxy population is antibiased up to z similar to 1.3. While at large redshifts similar to 3, we predict that the HI galaxies are strongly biased. Our bias evolution predictions are consistent with the observational bias results of Ly alpha galaxies.