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

Abstract

We present measurements of the size of the quasar proximity zone (Rp)for 11 low-luminosity (- -  M26.16 22.831450 )quasars at z∼6, discovered by the Subaru High-z Exploration of Low- Luminosity Quasars project. Our faint quasar sample expands the Rp measurement down to = - M 22.831450 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 μm or Mg II λ2798 emission lines. We also update the Rp measurements for 26 luminous quasars presented in Eilers et al. by using the latest systemic redshift results. The luminosity dependence on Rp 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 Rp, -Rp,corr25 (μ + - -  R z1p,corr25 3.79 1.72( ) )over   z5.8 6.6. This trend is steeper than that of Eilers et al., but significantly shallower than those of the earlier studies. Our results suggest that Rp,corr is insensitive to the neutral fraction of the universe at z∼6. Four quasars show exceptionally small -Rp,corr25 (0.90 proper Mpc), which could be the result of their young age (<104 yr)in the reionization epoch, though statistics on this are still scarce.