Intrinsic Absorption in Radio‐selected Quasars

Abstract

Moderate resolution spectra have been recorded for a sample of radio-selected QSOs (z ~ 2.5) discovered in the Faint Images of the Radio Sky at Twenty centimeters (FIRST) VLA survey. This work is motivated by the study of a heterogeneous set of QSO absorption line spectra that showed that as many as 36% of the absorbers normally thought to be intergalactic are correlated with physical properties of the background QSO, including the radio source spectral index. Spectra were taken for 24 newly discovered quasars in order to test this finding on a more homogeneous data set. The spectra have been searched for the most frequently observed absorption lines. The absorption line properties are compared to the radio properties of the quasars. The primary results are summarized as follows: (1) an excess of C IV absorbers in flat-spectrum quasars as compared to steep-spectrum quasars is confirmed (based on a total sample of 165 systems), (2) a small excess of high-velocity C IV absorbers is seen in radio-quiet QSOs as compared to radio-loud quasars, and (3) the Sloan Digital Sky Survey QSO spectra will allow for the detection of a high-velocity, narrow, intrinsic population of absorbers that is as small as 7% of the C IV absorber population in QSOs at z ~ 2.5.