(Re)solving reionisation with high-redshift analogues at cosmic noon

The bright Lyman-α (Lyα) line is a key observable in studies of galaxies in the early Universe. Lyα emitters (LAEs) are, by selection, in the very first stages of their formation. The Lyα line profile is a tracer of the escape fraction of ionising photons and the Lyα equivalent width and escape fraction trace the evolution of the neutral fraction of intergalactic gas. However, empirically, the Lyα production, escape and the line profile emerging from the ISM are poorly understood at high-redshift due to the typical limited spectral resolution and the lack of rest-frame optical spectra. Currently, cosmic noon (z~2) is the ideal redshift to study LAEs in detail. These galaxies resemble galaxies in the very early Universe with their similarly short formation times, extreme emission-lines and sizes. Importantly, the rest-frame optical lines are still observable from the ground at z~2. In my talk, I will present the first results of the 'XLS-z2' survey which is based on ~100 hours of VLT/X-SHOOTER observations of 30 LAEs at z~2 with stellar masses ~10^9 Msun. I will present the properties of the ISM and stellar populations that can be derived from their average UV to optical SED. I will focus in particular on the diversity in Lyα line profiles and what these tell us about the structure of the ISM in young distant galaxies. Finally, I will discuss the implications for the role of galaxies in the epoch of reionisation.