SIMBAD references

We present a detailed study of the longitudinal proximity effect using a sample of 85 quasars spanning an emission redshift range of 3.5 <= z_em <= 4.5 and Lyman continuum luminosity (L₉₁₂) ranging from 1.06 x 10³¹ to 2.24 x 10³² erg s^–1 Hz^–1. We use the high-quality spectra of these quasars obtained at a spectral resolution of R ∼ 5100 and S/N ∼ 30 using X-SHOOTER spectrograph mounted on the Very Large Telescope (VLT). In our analysis, we compared the transmitted flux and pixel optical depth of the Ly α absorption originating from the vicinity of quasars to those from the general intergalactic medium (IGM) by using a redshift-matched control sample. The longitudinal proximity effect is found up to r <= 12 Mpc (proper) from quasars. By appropriately scaling up the pixel optical depth in the vicinity of quasars to account for the excess ionization by quasars, we constrain the ratio of median H I optical depth in the vicinity of the quasar to that of the IGM (R_τ(r)). The R_τ(r) is found to be significantly higher than unity up to 6 Mpc from the quasar with a typical radial profile of the form R_τ(r) = 1 + A x exp(- r/r₀) with A = 9.16 ± 0.68 and r₀ = 1.27 ± 0.08 Mpc. The integrated value of the scaled pixel optical depth over the radial bin of 0-6 Mpc is found to be higher by a factor of 2.55 ± 0.17 than the corresponding integrated value of the median pixel optical depth of the IGM. We also found R_τ(r) to be luminosity dependent.