The Associated Absorption Features in Quasar Spectra of the Sloan Digital Sky Survey. I. Mg ii Absorption Doublets

Abstract

Using the SDSS spectra of quasars included in the DR7Q or DR12Q catalogs, we search for Mg II λλ2796,2803 narrow absorption doublets in the spectra data around Mg II λ2798 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 υ r < 6000 km s −1 is a safe boundary to constrain the vast majority of associated Mg II systems, although we find some doublets at υ r > 6000 km s −1 . If associated Mg II absorbers are defined by υ r < 6000 km s −1 , ∼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 λ2796 r ≥ 0.2 Å. 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 υ r distribution of the outflow Mg II absorbers is peaked at 1023 km s −1 , which is smaller than the corresponding value of the outflow C IV absorbers. The redshift number density evolution of absorbers (dn/dz) limited by υ r > −3000 km s −1 differs from that of absorbers constrained by υ r > 2000 km s −1 . While, absorbers limited by υ r > 2000 km s −1 and higher values exhibit similar profile of dn/dz. In addition, the dn/dz is smaller when absorbers are constrained with larger υ r . The distributions of equivalent widths, and the ratio of W λ2796 r /W λ2803 r is the same for associated and intervening systems, and independent on quasar luminosity.

Hunting for metals using XQ-100 Legacy Survey composite spectra

“…Various studies based on projected quasar pairs agree that quasar host galaxies at z > 1 exhibit a high incidence of optically thick, metal-enriched absorption systems traced by HI Lyα, CII, CIV and MgII absorption along the transverse direction at d 300 kpc, but low incidence along the foreground quasar sightline itself (Bowen et al 2006;Hennawi et al 2006;Shen & Ménard 2012;Farina et al 2013Farina et al , 2014Hennawi & Prochaska 2013;Prochaska et al 2014;Lau et al 2016;Lau et al 2018;Chen et al 2018). This contrast indicates that the ionizing emission from quasars is highly anisotropic, in qualitative agreement with the unified model of AGN (Antonucci 1993;Netzer 2015).…”

The Study of the Circumgalactic Medium with Quasar Pairs

“…Using large samples of LOS absorption lines, previous works (e.g., Chen & Pan 2017; Chen et al 2018a) claims that (1) the relative velocity of υ r < 6000 km s −1 with respect to quasar systemic redshifts is a safe boundary to constrain a vast majority of Mg II absorption lines from quasar's outflows, host galaxies, halos, and galaxy clusters; while (2) the velocity range of ±1500 km s −1 can well constrain the Mg II absorption lines formed within quasar's host galaxies, halos, and galaxy clusters. We also note from Chen et al (2018a) that the fraction of the intervening Mg II absorption lines is similar to that of the associated ones in the velocity range of υ r = 1500-6000 km s −1 . In other words, the associated Mg II absorption lines are significantly contaminated by the intervening ones in the velocity range of υ r = 1500-6000 km s −1 .…”

“…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.…”

The Physical Properties of Low Redshift FeLoBAL Quasars. I. Spectral Synthesis Analysis of the BAL Outflows using $SimBAL$

“…The absorption lines in this object, on the other hand, closely resembles the properties of an associated quasar absorber originating from a gas that is potentially located within the quasar host galaxy or its surrounding medium (Appendix D). In addition, this absorption system has been previously classified as an associated absorber in several catalogues (e.g., Quider et al 2011;Chen et al 2018); however, it is difficult to strictly differentiate between an outflow signature and an associated absorber therefore we proceed with caution in analyzing this outflow. Although this object was included in Farrah et al (2012), we excluded this BAL from the sample due to its ambiguous nature.…”