Probing the environment of high-z quasars using the proximity effect in projected quasar pairs

TL;DR

This study uses spectra of 181 quasar pairs to analyze the proximity effect around high-redshift quasars, revealing anisotropic ionization likely due to obscuration, and constraining quasar illumination in transverse versus longitudinal directions.

Contribution

It provides the first detailed comparison of the proximity effect in both directions around high-z quasars using a large sample, highlighting anisotropic obscuration effects.

Findings

Enhanced transmitted flux within 4 Mpc in longitudinal direction

Reversal of the trend in the transverse direction

Quasar illumination along the transverse is ≤27% of the longitudinal

Abstract

We have used spectra of 181 projected quasar pairs at separations $\le 1.5$ arcmins from the Sloan Digital Sky-Survey Data Release 12 in the redshift range of 2.5 to 3.5 to probe the proximity regions of the foreground quasars. We study the proximity effect both in the longitudinal as well as in the transverse directions, by carrying out a comparison of the \lya absorption lines originating from the vicinity of quasars to those originating from the general inter-galactic medium at the same redshift. We found an enhancement in the transmitted flux within 4 Mpc to the quasar in the longitudinal direction. However, the trend is found to be reversed in the transverse direction. In the longitudinal direction, we derived an excess overdensity profile showing an excess up to $r\leq 5$ Mpc after correcting for the quasar's ionization, taking into account the effect of low spectral resolution. This excess overdensity profile matches with the average overdensity profile in the transverse direction without applying any correction for the effect of the quasar's ionization. Among various possible interpretations, we found that the anisotropic obscuration of the quasar's ionization seems to be the most probable explanation. This is also supported by the fact that all of our foreground quasars happen to be Type-I AGNs. Finally, we constrain the average quasar's illumination along the transverse direction as compared to that along the longitudinal direction to be $\leq$27\% (3$\sigma$ confidence level).