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 \langle z \rangle _ { C~ { } { \sc iv } } = 2.2 and \langle z \rangle _ { Mg~ { } { \sc ii } } = 0.9 .
We find that , 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 _ { aa } ( r ) = { \left ( r _ { 0 } / r \right ) } ^ { \gamma } , with maximum–likelihood values of \gamma = 1.75 ^ { +0.50 } _ { -0.70 } and comoving r _ { 0 } = 3.4 ^ { +0.7 } _ { -1.0 } h ^ { -1 } Mpc ( q _ { 0 } = 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 \xi _ { 0 } ( z ) of the correlation function , as a function of redshift , from z = 3 to z = 0.9 .
We find that , when parametrized in the conventional manner as \xi _ { 0 } ( z ) \propto ( 1 + z ) ^ { - ( 3 + \epsilon ) + \gamma } , the amplitude grows with decreasing redshift , with maximum–likelihood value for the evolutionary parameter of \epsilon = 2.05 \pm 1.0 ( q _ { 0 } = 0.5 ) .
When extrapolated to zero redshift , the amplitude of the correlation function implies that the correlation length r _ { 0 } = 30 ^ { +22 } _ { -13 } h ^ { -1 } Mpc ( q _ { 0 } = 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 .