Subaru High-z Exploration of Low-luminosity Quasars (SHELLQs). XI. Proximity Zone Analysis for Faint Quasar Spectra at z ∼ 6

Abstract

We present measurements of the size of the quasar proximity zone ( R p ) for 11 low-luminosity ( ) quasars at z  ∼ 6, discovered by the Subaru High- z Exploration of Low-Luminosity Quasars project. Our faint quasar sample expands the R p measurement down to mag, where more common quasar populations dominate at the epoch. We restrict the sample to quasars whose systemic redshifts have been precisely measured by [C ii ] 158 μ m or Mg ii λ 2798 emission lines. We also update the R p measurements for 26 luminous quasars presented in Eilers et al. by using the latest systemic redshift results. The luminosity dependence on R p is found to be consistent with the theoretical prediction assuming a highly ionized intergalactic medium. We find a shallow redshift evolution of the luminosity-corrected R p , ( ) over . This trend is steeper than that of Eilers et al., but significantly shallower than those of the earlier studies. Our results suggest that R p ,corr is insensitive to the neutral fraction of the universe at z  ∼ 6. Four quasars show exceptionally small ( proper Mpc), which could be the result of their young age (<10 4 yr) in the reionization epoch, though statistics on this are still scarce.