Probing the intergalactic medium-galaxy connection toward PKS 0405-123. II. A cross-correlation study of Lyα absorbers and galaxies at z < 0.5

We present a pilot study of the clustering properties of Lyα absorbers with respect to known galaxies based on 112 Lyα absorbers and 482 galaxies identified at z < 0.5 along the sight line toward PKS 0405-123. The principal goal is to determine the origin of Lyα absorbers based on their cross-correlation amplitude with known galaxies and to investigate a possible N(H I) dependence of the cross-correlation function. The main results of our study are as follows: (1) The cross-correlation function ξ _ga measured using only emission-line-dominated galaxies and Lyα absorbers with log N(H I) ≥ 14 shows a comparable strength to the galaxy autocorrelation function ξ_gg on comoving, projected distance scales of less than 1 h^-1 Mpc, while there remains a lack of cross-correlation signal when using only absorption-line-dominated galaxies. This signifies a morphology-dependent ξ_ga and indicates that strong absorbers with log N(H I) ≥ 14 and emission-line galaxies reside in the same halo population. (2) A maximum likelihood analysis shows that Lyα absorbers with log N(H I) < 13.6 are consistent with being more randomly distributed with respect to known galaxies. (3) Finally, we find based on this single sight line that the amplitude of ξ_ga does not depend sensitively on N(H I) for strong absorbers, with log N(H I) ≥ 13.6.