The Clustering of C IV and Mg II Absorption-Line Systems

We have analyzed the clustering of C IV and Mg II absorption-line systems on comoving scales from 1 to 16 \hMpc, using an extensive catalog of heavy-element QSO absorbers with mean redshift 2.2 (C IV) and 0.9 (Mg II). For the C IV sample as a whole, the absorber line-of-sight correlation function is well fit by a power law of the form $\xi(r)=(r_0/r)^\gamma$, with maximum-likelihood values of $\gamma = 1.75 ^{+0.50}_{-0.70}$ and comoving $r_0 = 3.4 ^{+0.7}_{-1.0}$ \hMpc ($q_0=0.5$). This clustering is of the same form as that for galaxies and clusters at low redshift, and of amplitude such that absorbers are correlated on scales of clusters of galaxies. We also trace the evolution of the mean amplitude $\xi_0(z)$ of the correlation function from $z=3$ to $z=0.9$. We find that, when parametrized as $\xi_0(z)\propto (1+z)^{-(3+\epsilon)+\gamma}$, the amplitude grows rapidly with decreasing redshift, with maximum-likelihood value for the evolutionary parameter of $\epsilon = 2.05 \pm 1.0$. The rapid growth seen in the clustering of absorbers is consistent with gravitationally induced growth of perturbations.