Narrow C iv Absorption Lines with Multi-epoch Observations

Abstract

Using the quasar spectra from the Sloan Digital Sky Survey, all with two-epoch to six-epoch observations, we search for C IV λλ1548,1551 narrow absorption doublets in spectral data from the blue wing υ r = 30,000 km s−1 until the red wing of C IV λ1549 emission lines. We have obtained 21,239 C IV narrow absorption line (NAL) systems, of which 647 systems were significantly changed on timescales from ΔMJD = 0.24 to 1842.38 days at rest-frame. Both samples of the C IV NAL systems with multi-epoch observations and the variable C IV NAL systems are the largest ones to date. The offset velocity distribution of the variable C IV NALs from quasars has a peak at υ r ≈ 2000 km s−1 and gently extends to a larger offset velocity. There are 110 variable C IV NALs with υ r > 12,000 km s−1. In addition, about 10% intrinsic C IV NALs show time variability on a timescale of <2000 days. We find that the variations of C IV NALs are positively or negatively correlated with the alternations of quasar continua. The two kinds of correlations suggest that the variable C IV NALs included in our absorber catalog can be classified into at least two populations: (1) highly ionized systems that are dominated by highly ionized absorbing gas and negatively respond to the fluctuations of quasar emissions; and (2) lowly ionized systems that are dominated by lowly ionized absorbing gas and positively respond to fluctuations of quasar emissions. We also find that the absolute fractional changes in the absorption strengths of C IV NALs are inversely correlated with absorption strengths.

The Study of the Circumgalactic Medium with Quasar Pairs

“…The absorption lines with redshifts close to quasar systemic redshifts (z abs ≈ z em , associated absorption line) are likely formed in gaseous cloud physically associated with quasars themselves. Large samples (e.g., Shen & Menard 2012;Chen et al 2016;He et al 2017;Chen et al 2018aChen et al , 2018bChen et al , 2020Chen et al , 2022b of associated absorption lines have been available through systematically analyzing the quasar spectra from the Sloan Digital Sky Survey (SDSS; York et al 2000), which can often be used to comprehend the gas content of quasar systems along sight lines. The major shortcoming of associated absorption lines along quasar sight lines is that they cannot provide any information of gas content located on the transverse direction of quasars.…”