Cross-correlation of Lyman α absorbers with gas-rich galaxies

Abstract

The HI Parkes all-sky survey (HIPASS) galaxy catalogue is cross-correlated with known low redshift, low column density (N_HI < 10¹⁵cm^-2) Lyman α (Lyα) absorbers from the literature. The redshift-space correlation is found to be similar in strength to HIPASS galaxy self-clustering (correlation length s_0,ag= 6 +/- 4h^-1₁₀₀Mpc and s_0,gg= 3.1 +/- 0.5h^-1₁₀₀Mpc, respectively). In real space the cross-correlation is stronger than the galaxy auto-correlation (correlation length r_0,ag= 7.2 +/- 1.4h^-1₁₀₀Mpc and r_0,gg= 3.5 +/- 0.7h^-1₁₀₀Mpc, respectively) on scales from 1 to 10h^-1₁₀₀Mpc, ruling out the minihalo model for the confinement Lyα absorbers at the 99 per cent confidence level. Provided that the cause of the strong cross-correlation is purely gravitational, the ratio of correlation lengths suggest that absorbers are embedded in dark matter haloes with masses log(M/M_solar) = 14.2h^-1₁₀₀, similar to those of galaxy groups. The flattening of the cross-correlation at separations less than ~600h^-1₁₀₀kpc could correspond to the thickness of filaments in which absorbers are embedded. This work provides indirect statistical evidence for the notion that galaxy groups and large-scale filaments, particularly those that comprise gas-rich galaxies, are the dominant environments of low column density Lyα absorbers at z= 0.