The associated absorption features in quasar spectra of the Sload Digital Sky survey .I. \ absorption doublets
Abstract
Using the SDSS spectra of quasars included in the DR7Q or DR12Q catalogs, we search for Mg II narrow absorption doublets in the spectra data around Mg II emission lines. We obtain 17,316 Mg II doublets, within the redshift range of 0.3299<= zabs <= 2.5663. We find that a velocity offset of vr < 6000 km/s is a safe boundary to constrain the vast majority of associated Mg II systems, although we find some doublets at vr > 6000 km/s. If associated Mg II absorbers are defined by vr < 6000 km/s, ~33.3% of the absorbers supposed to be contaminants of intervening systems. Removing the 33.3% contaminants, ~4.5% of the quasars present at least one associated Mg II system with Wrλ2796>=0.2 . The fraction of associated Mg II systems with high velocity outflows correlates with the average luminosities of their central quasars, indicating a relationship between outflows and the quasar feedback power. The vr distribution of the outflow Mg II absorbers is peaked at 1023 km/s, which is smaller than the corresponding value of the outflow C IV absorbers. The redshift number density evolution of absorbers (dn/dz) limited by vr > -3000 km/s differs from that of absorbers constrained by vr > 2000 km/s. While, absorbers limited by vr > 2000 km/s and higher values exhibit similar profile of dn/dz. In addition, the dn/dz is smaller when absorbers are constrained with larger vr. The distributions of equivalent widths, and the ratio of Wrλ2796/Wrλ2803 is the same for associated and intervening systems, and independent on quasar luminosity.
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