Distant luminous Lyman- \alpha emitters ( LAEs ) are excellent targets for spectroscopic observations of galaxies in the epoch of reionisation ( EoR ) .
We present deep high-resolution ( R = 5000 ) VLT/X-SHOOTER observations , along with an extensive collection of photometric data of ‘ COLA1 ’ , a proposed double peaked LAE at z = 6.6 \citep Hu2016 .
We rule out that COLA1 ’ s emission line is an [ O ii ] doublet at z = 1.475 on the basis of i ) the asymmetric red line-profile and flux ratio of the peaks ( blue/red= 0.31 \pm 0.03 ) and ii ) an unphysical [ O ii ] /H \alpha ratio ( [ O ii ] /H \alpha > 22 ) .
We show that COLA1 ’ s observed B -band flux is explained by a faint extended foreground LAE , for which we detect Ly \alpha and [ O iii ] at z = 2.142 .
We thus conclude that COLA1 is a real double-peaked LAE at z = 6.593 , the first discovered at z > 6 , confirming the result from [ ] .
COLA1 is UV luminous ( M _ { 1500 } = -21.6 \pm 0.3 ) , has a high equivalent width ( EW _ { 0 , Ly \alpha } = 120 ^ { +50 } _ { -40 } Å ) and very compact Ly \alpha emission ( r _ { 50 , Ly \alpha } = 0.33 ^ { +0.07 } _ { -0.04 } kpc ) .
Relatively weak inferred H \beta + [ O iii ] line-emission from Spitzer /IRAC indicates an extremely low metallicity of Z < 1 / 20 Z _ { \odot } or reduced strength of nebular lines due to high escape of ionising photons .
The small Ly \alpha peak separation of 220 \pm 20 km s ^ { -1 } implies a low H i column density and an ionising photon escape fraction of \approx 15 - 30 % , providing the first direct evidence that such galaxies contribute actively to the reionisation of the Universe at z > 6 .
Based on simple estimates , we find that COLA1 could have provided just enough photons to reionise its own \approx 0.3 pMpc ( 2.3 cMpc ) bubble , allowing the blue Ly \alpha line to be observed .
However , we also discuss alternative scenarios explaining the detected double peaked nature of COLA1 .
Our results show that future high-resolution observations of statistical samples of double peaked LAEs at z > 5 are a promising probe of the occurrence of ionised regions around galaxies in the EoR .