Associated absorption and radio source growth

Abstract

Results are presented from a survey for CIV associated absorption in a complete low-frequency-selected sample of quasars. In agreement with previous work, associated absorbers are most common in steep-spectrum and lobe-dominated quasars, indicative of an anisotropic cloud distribution. Furthermore, we find the strongest CIV absorption occurs in sources of small radio size, suggesting that the absorbing clouds are destroyed or displaced as radio sources expand. Evidence for dust in the clouds is also found, such that quasars with strong absorption are systematically redder. Finally, we find no evidence for evolution in the frequency or properties of the absorbers from z~0.7 to z~3.