We use high-resolution hydrodynamical simulations to investigate the spatial correlation between weak ( N _ { HI } < 10 ^ { 15 } cm ^ { -2 } ) Ly \alpha absorbers and gas–rich galaxies in the local universe .
We confirm that Ly \alpha 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 r _ { 0 ,gg } = 3.1 \pm 0.1 \mbox { Mpc $h ^ { -1 } $ } and r _ { 0 ,ag } = 1.4 \pm 0.1 \mbox { Mpc $h ^ { -1 } $ } , respectively ) , in contrast with the recent results of ( , RW06 ) , 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 RW06 .
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 datasets is \sim 1 - \sigma only .