JWST FRESCO: A comprehensive census of H β + [O iii] emitters at 6.8 < z < 9.0 in the GOODS fields

Abstract

We present the census of H + [] emitters at from the JWST FRESCO survey over 124 arcmin in the GOODS-North and GOODS-South fields. Our unbiased spectroscopic search results in 137 spectroscopically confirmed galaxies at with observed [] fluxes. The rest-frame optical line ratios of the median stacked spectrum (median) indicate negligible dust attenuation, low metallicity () and a high ionization parameter. We find a factor difference in the number density of galaxies between GOODS-South and GOODS-North, which is caused by a single overdensity at in GOODS-North. The bright end of the UV luminosity function of spectroscopically confirmed [] emitters is in good agreement with HST dropout-selected samples. Discrepancies between the observed [] LF, []/UV ratio, and [] equivalent widths, and that predicted by theoretical models, suggest burstier star-formation histories and/or more heterogeneous metallicity and ionizing conditions in galaxies. We report a rapid decline of the [] luminosity density at which cannot be explained by the evolution of the cosmic star-formation rate density. Finally we find that FRESCO detects in only 2h galaxies likely accounting for of the ionizing budget at (assuming an escape fraction of), raising the prospect of directly detecting a significant fraction of the sources of reionization with JWST.