The role of galaxies and AGN in reionising the IGM -- III : IGM-galaxy
  cross-correlations at z~6 from 8 quasar fields with DEIMOS and MUSE
  We present improved results of the measurement of the correlation between
galaxies and the intergalactic medium (IGM) transmission at the end of
reionisation. We have gathered a sample of $13$ spectroscopically confirmed
Lyman-break galaxies (LBGs) and $21$ Lyman-$\alpha$ emitters (LAEs) at angular
separations $20'' \lesssim \theta \lesssim 10'$ ($\sim 0.1-4$ pMpc at $z\sim
6$) from the sightlines to $8$ background $z\gtrsim 6$ quasars. We report for
the first time the detection of an excess of Lyman-$\alpha$ transmission spikes
at $\sim 10-60$ cMpc from LAEs ($3.2\sigma$) and LBGs ($1.9\sigma$). We
interpret the data with an improved model of the galaxy-Lyman-$\alpha$
transmission and two-point cross-correlations which includes the enhanced
photoionisation due to clustered faint sources, enhanced gas densities around
the central bright objects and spatial variations of the mean free path. The
observed LAE(LBG)-Lyman-$\alpha$ transmission spike two-point cross-correlation
function (2PCCF) constrains the luminosity-averaged escape fraction of all
galaxies contributing to reionisation to $\langle f_{\rm esc} \rangle_{M_{\rm
UV}<-12} = 0.14_{-0.05}^{+0.28}\,(0.23_{-0.12}^{+0.46})$. We investigate if the
2PCCF measurement can determine whether bright or faint galaxies are the
dominant contributors to reionisation. Our results show that a contribution
from faint galaxies ($M_{\rm UV} > -20 \, (2\sigma)$) is necessary to reproduce
the observed 2PCCF and that reionisation might be driven by different
sub-populations around LBGs and LAEs at $z\sim 6$.
