The Form and Evolution of the Clustering of QSO Heavy‐Element Absorption‐Line Systems

Abstract

We have analyzed the clustering of C IV and Mg II absorption-line systems on comoving scales r from 1 to 16 h-1 Mpc, using an extensive catalog of heavy-element QSO absorbers with mean redshift zC IV = 2.2 and zMg II = 0.9. We find that, for the C IV sample as a whole, the absorber line-of-sight correlation function is well fitted by a power law of the form ξaa(r) = (r0/r)γ, with maximum-likelihood values of γ=1.75 -->−0.70+0.50 and comoving r -->0=3.4 -->+ 0.7−1.0 h-1 Mpc (q0 = 0.5). The clustering of absorbers at high redshift is thus of a form that is consistent with that found for galaxies and clusters at low redshift, and of amplitude such that absorbers are correlated on scales of galaxy clusters. We also trace the evolution of the mean amplitude ξ0(z) of the correlation function, as a function of redshift, from z = 3 to z = 0.9. We find that, when parameterized in the conventional manner as ξ0(z) (1 + z)-(3+)+γ, the amplitude grows with decreasing redshift, with a maximum-likelihood value for the evolutionary parameter of = 2.05 ± 1.0 (q0 = 0.5). When extrapolated to zero redshift, the amplitude of the correlation function implies that the correlation length r -->0=30 -->−13+22 h-1 Mpc (q0 = 0.5). This suggests that strong C IV and Mg II absorbers, on megaparsec scales, are biased tracers of the higher density regions of space and that agglomerations of strong absorbers along a line of sight are indicators of clusters and superclusters. This is supported by recent observations of Lyman break galaxies. The growth seen in the clustering of absorbers is consistent with gravitationally induced growth of perturbations.