Strong Clustering in the Low Redshift Lyman-$α$ Forest

Abstract

The two-point correlation function, $ξ$, of Lyman-alpha forest is found to be large, $ξ= 1.8^{+1.6}_{-1.2}$, > 90% confidence level, on the scale of 250-500 km/s for a sample of absorbers (0 < z < 1.3) assembled from HST Key Project Observations. This correlation function is stronger than at high redshift (z > 1.7) where $ξ\approx 0.2$ for velocities > 250 km/s.