Catalog of narrow Mg II absorption lines in the baryon oscillation spectroscopic survey.
CHEN Z.-F., GU Q.-S. and CHEN Y.-M.
Abstract (from CDS):
Using the Data Release 9 Quasar spectra from the Baryonic Oscillation Spectroscopic Survey, which does not include quasar spectra from the Sloan Digital Sky Survey Data Release 7, we detect narrow Mg II λλ2796, 2803 absorption doublets in the spectral data redward of 1250 Å (quasar rest frame) until the red wing of the Mg II λ2800 emission line. Our survey is limited to quasar spectra with a median signal-to-noise ratio <S/N> ≥ 4/ pixel in the surveyed spectral region, resulting in a sample that contains 43,260 quasars. We have detected a total of 18,598 Mg II absorption doublets with 0.2933 ≤ zabs≤ 2.6529. About 75% of absorbers have an equivalent width at rest frame of Wrλ2796. About 75% of absorbers have doublet ratios (DR = Wrλ2796/Wrλ2803) in the range of 1 ≤ DR ≤ 2, and about 3.2% lie outside the range of 1 - σDR≤ DR ≤ 2 + σDR. We characterize the detection false positives/negatives by the frequency of detected Mg II 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 Mg II 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 (β) of Mg II absorbers have a complex distribution which probably consists of three classes of Mg II 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 β distribution of the Mg II might mainly be contributed by the quasar outflow absorbers and peaks at υ ≈ 1500 km/s. This peak velocity is lower than the value of 2000 km/s found in statistical analysis of C IV absorbers.