The Study of the Circumgalactic Medium with Quasar Pairs 

Abstract

We have collected 10,025 foreground–background quasar pairs with projected distances d p < 500 kpc from the large quasar catalog of the Sloan Digital Sky Survey DR16Q. We investigate the properties of the Mg ii absorption lines with W r > 0.15 Å around foreground quasars, including both the line of sight (LOS; of foreground quasars) and transverse (TRA; perpendicular to the LOS) absorptions. Both the equivalent width (the correlation coefficient ρ = −0.915 and the probability P < 10−4 of no correlation) and incident rate (ρ = −0.964 and P < 10−6) of TRA Mg ii absorption lines are obviously anticorrelated with projected distance. The incident rate of TRA Mg ii absorption lines is obviously (>4σ) greater than that of LOS Mg ii absorption lines at projected distances d p < 200 kpc, while the TRA and LOS Mg ii both have similar (<3σ) incident rates at scales d p > 200 kpc. The anisotropic radiation from quasars would be the most possible interpretation for the anisotropic absorption around quasars. This could also indicate that the quasar radiation is not obviously impacting the gas halos of quasars at scales d p > 200 kpc.

Discovery of Optically Emitting Circumgalactic Nebulae around the Majority of UV-luminous Quasars at Intermediate Redshift

“…Empirical characterizations of cool CGM around quasars have advanced significantly in the last decade, thanks to a combination of large ground-based surveys like SDSS that enable studies of Mg II absorption at z  2 (e.g., Bowen et al 2006;Farina et al 2014;Johnson et al 2015;Z.-F. Chen et al 2023), dedicated absorption surveys with large telescopes at z = 2-4 in rest-UV absorption (e.g., Hennawi et al 2006;Prochaska et al 2013;Lau et al 2016), and observations of Lyα emission nebulae at z > 2 (e.g., Borisova et al 2016;Cai et al 2019;O'Sullivan et al 2020;Fossati et al 2021;Mackenzie et al 2021). The discovery of rest-frame optical emission from >20 to 30 kpc ionized nebulae around the majority of UV-luminous quasars at z = 0.4-1.4 represents a new opportunity to study the relationship between cool CGM and the galactic systems they surround, while also opening a new set of physical diagnostics based on nonresonant emission lines.…”