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

We have analyzed the clustering of C IV and Mg II absorption-line systems oncomoving scales from 1 to 16 \hMpc, using an extensive catalog of heavy-elementQSO absorbers with mean redshift 2.2 (C IV) and 0.9 (Mg II). We find that, forthe C IV sample as a whole, the absorber line-of-sight correlation function iswell-fit by a power law with index $\gamma = 1.75 ^{+0.50}_{-0.70}$ andcomoving correlation length $r_0 = 3.4 ^{+0.7}_{-1.0}$ \hMpc ($q_0=0.5$). Theclustering of absorbers at high redshift is thus of a form like that ofgalaxies and clusters at low redshift, and of amplitude such that absorbers arecorrelated on scales of galaxy clusters. We also trace the evolution of themean amplitude $\xi_0(z)$ of the correlation function from $z=3$ to $z=0.9$. Wefind that, when parametrized as $\xi_0(z)\propto (1+z)^{-(3+\epsilon)+\gamma}$,the amplitude grows rapidly with decreasing redshift, with maximum-likelihoodvalue for the evolutionary parameter of $\epsilon = 2.05 \pm 1.0$ ($q_0=0.5$).When extrapolated to zero redshift, the correlation length is $r_0 = 30^{+22}_{-13}$ \hMpc . This suggests that the strong C IV and Mg II absorbers,on megaparsec scales, are biased tracers of the higher-density regions ofspace, and that agglomerations of strong absorbers along a line of sight areindicators of clusters and superclusters. This is supported by recentobservations of ``Lyman break'' galaxies. The rapid growth seen in theclustering of absorbers mimics that expected in a a critical universe fromlinear theory of gravitational instability, and is consistent withgravitationally induced growth of perturbations.Comment: 26 pages (LaTex, uses aaspp4.sty), with 8 encapsulated PostScript figures. Includes an augmented discussion of the close relationship between strong absorbers, clusters, and ``Lyman break'' galaxies. To appear in The Astrophysical Journal, vol. 500, June 10, 199