Three Lyman-alpha emitting galaxies within a quasar proximity zone at z=5.8

Abstract

Quasar proximity zones at $z>5.5$ correspond to over-dense and over-ionized environments. Galaxies found inside proximity zones can therefore display features which would otherwise be masked by absorption in the IGM. We demonstrate the utility of this quasar-galaxy synergy by reporting the discovery of the first three `proximate Lyman-$\alpha$ emitters' (LAEs) within the proximity zone of quasar J0836 at $z=5.802$ (\textit{Aerith A, B} and \textit{C}). \textit{Aerith A}, located behind the quasar with an impact parameter $D_\perp = 278$ pkpc, provides the first detection of a Lyman-$\alpha$ transverse proximity effect. We model the transmission and show it constrains the onset of J0836's quasar phase to $0.2 \text{Myr}<t<20\text{Myr}$ in the past. The second object, \textit{Aerith B} at a distance $D=750$ pkpc from the quasar, displays a bright, broad double-peaked \lal emission line. Based on relations calibrated at $z\leq3$, the peak separation implies a low ionizing $f_{\text{esc}} \lesssim 1\%$, the most direct such constraint on a reionization-era galaxy. We fit the Ly-$\alpha$ line with an outflowing shell model, finding a completely typical central density $\text{log N}_{\text{HI}}/\text{cm}^{-2} = 19.3_{-0.2}^{+0.8}$, outflow velocity $v=16_{-11}^{+4}$ km s$^{-1}$, and gas temperature $\text{log} T/\text{K} = 3.8_{-0.7}^{+0.8}$ compared to $2<z<3$ analogue LAEs. Finally, we detect an emission line at $\lambda=8177$ \AA\ in object \textit{Aerith C} which, if it is \lal at $z=5.726$, would correspond closely with the end of the quasar's proximity zone ($\Delta z<0.02$ from the boundary) and suggests the quasar influences the IGM up to $\sim85$ cMpc away, making it the largest quasar proximity zone. Via the analyses conducted here, we illustrate how proximate LAEs offer unique insight into the ionizing properties of both quasars and galaxies during the epoch of reionization.