# The Study of Circumgalactic Medium with Quasar Pairs

## TL;DR

This study analyzes Mg II absorption lines around quasars using a large quasar pair dataset, revealing anisotropic gas distribution and quasar radiation effects within 200 kpc.

## Contribution

It provides the first large-scale statistical analysis of Mg II absorption around quasars, highlighting anisotropic absorption patterns and the limited impact of quasar radiation beyond 200 kpc.

## Key findings

- TRA Mg II absorption is more frequent than LOS at <200 kpc.
- Absorption strength and rate decrease with distance from quasars.
- Quasar radiation likely causes anisotropic gas distribution.

## Abstract

We have collected 10025 foreground-background quasar pairs with projected distances $d_p<500$ kpc from the large quasar catalog of the SDSS DR16Q. We investigate the properties of the Mg II absorption lines with $W_r>0.15$ \AA\ around foreground quasars, including both the LOS (line-of-sights of foreground quasars) and transverse (TRA, perpendicular to the LOS) absorptions. Both the equivalent width (the correlation coefficient $\rho=-0.915$ and the probability $P < 10^{-4}$ of no correlation) and incident rate ($\rho=-0.964$ and $P < 10^{-6}$) of TRA \Mgii\ absorption lines are obviously anti-correlated with projected distance. The incident rate of TRA \Mgii\ absorption lines is obviously ($>4\sigma$) greater than that of LOS \Mgii\ absorption lines at projected distances $d_p<200$ kpc, while the TRA and LOS \Mgii\ both have similar ($<3\sigma$) 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.