AN EXCESS OF C-IV ABSORBERS IN LUMINOUS QUASARS - EVIDENCE FOR GRAVITATIONAL LENSING

We have compiled a new and extensive catalog of heavy-element QSO abso rption-line systems and analyzed the distribution of absorbers in brig ht and faint QSOs, to search for gravitational lensing of background Q SOs by the matter associated with the absorbers. There is a highly sig nificant excess of C IV absorbers in bright QSOs in the redshift range z = 1.2-3.2, and this excess increases strongly as a function of QSO absolute magnitude. No significant excess is found for Mg II absorbers in the redshift range z = 0.30-1.55. We rule out several possible rea sons for this effect and argue that the C IV excess could be due to gr avitational lensing. If so, then the lensing masses must be at z great er than or similar to 1.5 and within several hundred comoving megapars ecs of the QSOs, where the C IV absorbers are mainly found. The absenc e of an excess in the available Mg II sample would then arise because the Mg II data do not sample this region of space.