Evolution of the observed Ly alpha luminosity function from z=6.5 to z=7.7: evidence for the epoch of reionization?

Aims. Ly alpha emitters (LAEs) can be detected out to very high redshifts during the epoch of reionization. The evolution of the LAE luminosity function with redshift is a direct probe of the Ly alpha transmission of the intergalactic medium (IGM), and therefore of the IGM neutral-hydrogen fraction. Measuring the Ly alpha luminosity function (LF) of Lya emitters at redshift z = 7.7 therefore allows us to constrain the ionizing state of the Universe at this redshift.