Cake Talk by Romain Meyer

With the advent of JWST, rest-frame optical emission lines have become observable for the first time in reionisation-era galaxies. In particular, early NIRCam WFSS and NIRSPec MSA observations have revealed numerous strong [OIII], Hβ and H⍺ emitters at z~5-10, in apparent disagreement with the predictions of a number of theoretical models. Larger samples and wide-area coverage are however necessary to conclude on the possible implications for early galaxy evolution and reionisation. In this talk I will present a volume-complete, unbiased sample of 137 [OIII] and Hβ emitters at 6.8 < z < 9 drawn from FRESCO. FRESCO observes the GOODS-North/South fields (124 arcmin^2) with NIRCam slitless spectroscopy (F444W), providing redshifts for [OIII] emitters with line fluxes down to ~1e-18 cgs and pushing the high-redshift frontier for the [OIII] luminosity function from z~3 to z~9. This unbiased sample provides a statistical basis for future analysis of typical reionisation-era line emitters observed with JWST, and delivers new important constraints on early galaxy evolution. In particular, I will present the median properties of OIII emitters using the stacked rest-frame optical lines, the luminosity function and number density of z > 6.8 OIII emitters, as well as the presence of over-/under-densities. The OIII luminosity function and OIII/UV ratios distribution measurements reveal discrepancies with simulations of the early Universe suggesting that z > 6 galaxies have more bursty star-formation histories and/or are more metal-poor than predicted. Finally, I will present preliminary result from a JWST programme aiming to calibrate indirect escape fraction tracers directly in the Epoch of Reionisation. I will discuss how, with such calibrations in hand, future JWST observations could directly detect and map the sources of reionisation in 3D.