Narrow MgII absorption lines from SDSS-DR9Q

We characterize the detection false positives/negatives by the frequency of detected MgII absorption doublets in the limits of the S/N of the spectral data. The S/N=4.5 limit is assigned a completeness fraction of 53% and tends to be complete when the S/N is greater than 4.5. The redshift number densities of all of the detected MgII absorbers moderately increase from z~0.4 to z~1.5, which parallels the evolution of the cosmic star formation rate density.

Limiting our investigation to those quasars whose emission redshift can be determined from narrow emission lines, the relative velocities ({beta}) of MgII absorbers have a complex distribution which probably consists of three classes of MgII absorbers: (1) cosmologically intervening absorbers; (2) environmental absorbers that reside within the quasar host galaxies or galaxy clusters; (3) quasar outflow absorbers. After subtracting contributions from cosmologically intervening absorbers and environmental absorbers, the {beta} distribution of the MgII might mainly be contributed by the quasar outflow absorbers and peaks at {upsilon}~1500km/s.

This peak velocity is lower than the value of 2000km/s found in statistical analysis of CIV absorbers.