The relation between Lyman α absorbers and gas-rich galaxies in the local Universe

Abstract

We use high-resolution hydrodynamical simulations to investigate the spatial correlation between weak (NHI < 1015 cm-2) Lyα absorbers and gas-rich galaxies in the local Universe. We confirm that Lya absorbers are preferentially expected near gas-rich galaxies and that the degree of correlation increases with the column density of the absorber. The real-space galaxy auto-correlation is stronger than the cross-correlation (correlation lengths r0,gg = 3.1 ± 0.1 Mpc h-1 and r0,ag = 1.4 ± 0.1 Mpc h-1, respectively), in contrast with the recent results of Ryan-Weber, and the auto-correlation of absorbers is very weak. These results are robust to the presence of strong galactic winds in the hydrodynamical simulations. In redshift space, a further mismatch arises since at small separations the distortion pattern of the simulated galaxy-absorber cross-correlation function is different from the one measured by Ryan-Weber. However, when sampling the intergalactic medium along a limited number of lines-of-sight, as in the real data, uncertainties in the cross-correlation estimates are large enough to account for these discrepancies. Our analysis suggests that the statistical significance of difference between the cross-correlation and auto-correlation signal in current data sets is ~1σ only. © 2008 The Authors. Journal compilation © 2008 RAS.