  The HI Parkes All Sky Survey (HIPASS) galaxy catalogue is cross-correlated
with known low redshift, low column density (N_HI <10^15 cm^-2) Lyman-alpha
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+/-4 and s_0,gg=3.1+/-0.5 h^-1 Mpc respectively). In real-space the
cross-correlation is stronger than the galaxy auto-correlation (correlation
length r_0,ag=7.2+/-1.4 and r_0,gg=3.5+/-0.7 h^-1 Mpc respectively) on scales
from 1-10 h^-1 Mpc, ruling out the mini-halo model for the confinement
Lyman-alpha absorbers at the 99 percent 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/Msun)=14.2 h^-1, similar to those of galaxy groups. The
flattening of the cross-correlation at separations less than ~600 h^-1 kpc
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 Lyman-alpha
absorbers at z=0.
