Occurrence and Global Properties of Narrow Civλ1549 Å Absorption Lines in Moderate‐Redshift Quasars1

A statistical study is presented of (a) the frequency of narrow CIV lambda1549 absorption lines in 1.5 <~ z <~ 3.6 radio-quiet and radio-loud quasars,and of (b) the UV and radio properties of the absorbed quasars. The quasarsample is unbiased with respect to absorption properties and the radio-quietand radio-loud subsamples are well matched in redshift and luminosity. Asimilarly high incidence (>~50%) of narrow CIV absorbers is detected for theradio-quiet and radio-loud quasars, and a constant ~25% of all the quasars,irrespective of radio type display associated CIV absorbers stronger than arest equivalent width of 0.5A. Both radio-quiet and radio-loud quasars withnarrow absorption lines have systematically redder continua, especiallystrongly absorbed objects. There is evidence of inclination dependent dustreddening and absorption for the radio quasars. An additional key result isthat the most strongly absorbed radio quasars have the largest radio sourceextent. This result is in stark contrast to a recent study of the low-frequencyselected Molonglo survey in which a connection between the strength of thenarrow absorbers and the (young) age of the radio source has been proposed. Thepossible origin of these discrepant results is discussed and may be related tothe higher source luminosity for the quasars studied here.Comment: 28 pages, including 10 figures and 8 tables. To appear in ApJ, 599, December 200