Homogeneous measurements of proximity zone sizes for 59 quasars in the Epoch of Reionization

ABSTRACT The overionized regions surrounding high-redshift quasars, known as proximity zones, provide a window into the interaction between supermassive black holes and the intergalactic medium (IGM) during the epoch of reionization. We present new homogeneous measurements of proximity zone sizes ($R_{\mathrm{p}}$) for a sample of 59 quasars spanning redshifts $5.77 \le z \le 7.54$ (median $z = 6.59$). For 15 of these sources, we measure $R_{\mathrm{p}}$ for the first time. The quasars in our catalogue have absolute magnitudes at rest-frame 1450 Å in the range $-29.13 \le M_{1450} \le -25.20$ (median $M_{1450} \simeq -26.49$), providing one of the most extensive data sets for exploring $R_{\mathrm{p}}$ at these epochs. The distribution of $R_{\mathrm{p}}$ values shows a large scatter at fixed redshift and luminosity, likely reflecting variations in quasar lifetimes ($t_{\mathrm{Q}}$), IGM density fluctuations, and IGM neutral fraction. We fit a bivariate power-law model to a large sample of 100 objects to study the dependence of $R_{\mathrm{p}}$ with both $M_{1450}$ and z: we find that the evolution of $R_{\mathrm{p}}$ with luminosity is in agreement with the models ($R_{\mathrm{p}} \propto 10^{-0.4 M_{1450}/2.87}$), while the evolution of $R_{\mathrm{p}}$ with z is steeper than previous works ($R_{\mathrm{p}} \propto (1+z)^{-2.44}$). We identify 13 quasars with small proximity zone size, defined using the residuals of our fit. In all cases, except for J2211–6320, we rule out the presence of associated dense absorbers that prematurely truncate $R_{\mathrm{p}}$, and suggest a short $t_{\mathrm{Q}}$ ($\lesssim 10^4$ yr) as a possible explanation for their small proximity zone sizes.