Narrow CIV absorption doublets on quasar spectra of the Baryon Oscillation Spectroscopic Survey

Abstract

In this paper, we extend our work of Papers I and II, which are assigned to systematically survey C IV λλ1548,1551 narrow absorption lines (NALs) with zabs ≪ zem on quasar spectra of the Baryon Oscillation Spectroscopic Survey (BOSS) to collect CIV NALs with zabs ≈ zem from blue to red wings of C IV λ1549 emission lines. Together with Papers I and II, we have collected a total number of 41 479 C IV NALs with 1.4544 ≤ zabs ≤ 4.9224 in surveyed spectral region redward of Lyα until red wing of CIV λ1549 emission line. We find that the stronger CIV NALs tend to be the more saturated absorptions, and associated systems (zabs ≈ zem) seem to have larger absorption strengths when compared to intervening ones (zabs ≪zem). The redshift density evolution behaviour of absorbers (the number of absorbers per redshift path) is similar to the history of the cosmic star formation. When compared to the quasar-frame velocity (β) distribution of Mg II absorbers, the β distribution of C IV absorbers is broader at β ≈ 0, shows longer extended tail, and exhibits a larger dispersion for environmental absorptions. In addition, for associated CIV absorbers, we find that low-luminosity quasars seem to exhibit smaller β and stronger absorptions when compared to high-luminosity quasars.