We present a study of a double-peaked Ly$\alpha$ emitter, named LAE-11, found in the proximity zone of QSO J0910-0414 at $z\sim6.6$. We use a combination of deep photometric data from Subaru Telescope, HST, and JWST with spectroscopic data from Keck/DEIMOS, NIRCam WFSS and NIRSpec MSA to characterise the ionising and general properties of the galaxy, as well as the quasar environment surrounding it. We detect Ly$\alpha$, H$\beta$, [OIII] doublet, and H$\alpha$ emission lines in the various spectral datasets. The presence of a double-peaked Ly$\alpha$ line in the spectrum allows us to characterise the opening angle and lifetime of the QSO as $\theta_Q>49.62${ \deg} and $t_Q > 3.8\times10^5$ years. LAE-11 is a fairly bright (M$_\rm{ UV} = -19.84^{ +0.14}_{ -0.16}$), blue galaxy with a UV slope of $\beta = -2.61^{ +0.06}_{ -0.08}$. Since the galaxy is located in a quasar-ionised region, we have a unique opportunity to measure the escape fraction of Lyman Continuum photons using the un-attenuated double-peaked Ly$\alpha$ emission profile and its equivalent width at such high redshift. We employ diagnostics which do not rely on the detection of Ly$\alpha$ for comparison, and find that all tracers of ionising photon leakage agree within 1$\sigma$ uncertainty. We measure a moderate escape of Lyman Continuum photons from LAE-11 of $f_\rm{ esc}^\rm{ LyC} = (8 - 33)\%$. Detections of both H$\alpha$ and H$\beta$ emission lines allow for separate measurements of the ionising photon production efficiency, resulting with $\log(\xi_\rm{ ion}/\rm{ Hz~erg^{ -1}}) = 25.59\pm0.08$ and $25.65\pm0.09$, for H$\alpha$ and H$\beta$, respectively. The total ionising output of LAE-11, $\log(f_\rm{ esc}^\rm{ LyC}\xi_\rm{ ion, H\alpha}/\rm{ Hz~erg^{ -1}}) = 24.85^{ +0.24}_{ -0.34}$, is higher than the value of $24.3 - 24.8$ which is traditionally assumed as needed to drive Reionisation forward.
Categories: astro-ph.GA