The associated absorption features in quasar spectra of the Sload Digital Sky survey .I. \MgII\ absorption doublets

TL;DR

This study analyzes Mg II absorption doublets in SDSS quasar spectra, revealing their velocity distribution, association with quasar luminosity, and evolution, providing insights into quasar outflows and feedback mechanisms.

Contribution

It provides a large statistical analysis of Mg II associated absorbers, establishing velocity boundaries, and exploring their relation to quasar properties and evolution, which is novel in scope and detail.

Findings

33.3% of Mg II absorbers are contaminants when using v_r<6000 km/s boundary.

Associated Mg II systems are present in about 4.5% of quasars with W_r>=0.2 Å.

Higher quasar luminosity correlates with increased high-velocity Mg II outflows.

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<= z_abs <= 2.5663. We find that a velocity offset of v_r < 6000 km/s is a safe boundary to constrain the vast majority of associated Mg II systems, although we find some doublets at v_r > 6000 km/s. If associated Mg II absorbers are defined by v_r < 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 W_r\lambda2796>=0.2 \AA. 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 v_r 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 v_r > -3000 km/s differs from that of absorbers constrained by v_r > 2000 km/s. While, absorbers limited by v_r > 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 v_r. The distributions of equivalent widths, and the ratio of W_r\lambda2796/W_r\lambda2803 is the same for associated and intervening systems, and independent on quasar luminosity.