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

We have used spectra of 181 projected quasar pairs at separation $\le 1.5$ arcmin 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 statistical comparison of the Ly$\alpha$ absorption lines originating from the vicinity of quasars to those originating from the general inter-galactic medium (IGM). This was done using a control sample of IGM, matched in absorption redshift and signal-to-noise ratio to that of our sample probing the proximity region. In our analysis, we found that the ratio of the observed median optical depths of the proximity region ($\langle\tau_{prox}\rangle$) and the IGM ($\langle \tau_{IGM}\rangle$) around the quasar within $r<3$ Mpc differs in the longitudinal and the transverse directions, having values $\sim$0.84 and $\sim$1.14 which deviates from unity at 2.13$\sigma$ and 2.30$\sigma$ level respectively. However, after taking into account the corrections due to excess ionization from the quasars, validated for spectra at SDSS resolution using detailed simulations, we found that the corrected $\langle\tau_{prox}\rangle/\langle\tau_{IGM}\rangle$ steeply increase towards the quasar both in the longitudinal and the transverse directions. The average value of the corrected $\langle\tau_{prox}\rangle/\langle\tau_{IGM}\rangle$ are 1.53 and 1.76 (within $r<3$ Mpc) deviating from unity at 3.84$\sigma$ and 9.26$\sigma$ significance respectively. The difference of the corrected $\langle\tau_{prox}\rangle/\langle\tau_{IGM}\rangle$ values (within $r<3$ Mpc) among these two directions is found to be significant at 2.11$\sigma$ level, being higher in the transverse direction. We discuss the possible scenarios that can explain this observed difference.