The relation between Lyman-alpha absorbers and gas--rich galaxies in the local universe

TL;DR

This study uses high-resolution hydrodynamical simulations to explore how weak Lyman-alpha absorbers are spatially related to gas-rich galaxies in the local universe, revealing a correlation that depends on absorber strength.

Contribution

It provides new insights into the spatial correlation between Ly-alpha absorbers and gas-rich galaxies, contrasting previous observational results and demonstrating robustness against galactic winds.

Findings

Ly-alpha absorbers are more likely near gas-rich galaxies.

Correlation strength increases with absorber column density.

Real-space auto-correlation of galaxies is stronger than cross-correlation with absorbers.

Abstract

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 Mpc/h and r_{0,ag}=1.4 \pm 0.1 Mpc/h, respectively), in contrast with the recent results of Ryan-Weber (2006, 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 ~ 1-sigma only.