Date: 11/11/2024
Harvard ADS: JWST FRESCO: a comprehensive census of H β + [O III] emitters at 6.8 < z < 9.0 in the GOODS fields
Paper abstract: We present the census of H \beta + [{\rm O\, {\small III}}] 4960,5008\rm{\mathring{\rm\,A}} emitters at 6.8\lt z\lt 9.0 from the JWST FRESCO survey over 124 arcmin^2 in the GOODS-North and GOODS-South fields. Our unbiased spectroscopic search results in 137 spectroscopically confirmed galaxies at 6.8\lt z\lt 9.0 with observed [{\rm O\, {\small III}}] fluxes f_{\rm { [{\rm O\, {\small III}}]}}\gtrsim 1\times 10^{-18}\ \rm {ergs}\ \rm {s}^{-1} \ \rm {cm}^{-2}. The rest-frame optical line ratios of the median stacked spectrum (median M_{\rm {UV}}=-19.65^{+0.59}_{-1.05}) indicate negligible dust attenuation, low metallicity (12+\log (\rm {O/H})= 7.2-7.7) and a high ionization parameter \log _{10}U ~eq -2.5. We find a factor \times 1.3 difference in the number density of 6.8\lt z\lt 9.0 galaxies between GOODS-South and GOODS-North, which is caused by a single overdensity at 7.0\lt z\lt 7.2 in GOODS-North. The bright end of the UV luminosity function of spectroscopically confirmed [{\rm O\, {\small III}}] emitters is in good agreement with HST dropout-selected samples. Discrepancies between the observed [{\rm O\, {\small III}}] LF, [{\rm O\, {\small III}}]/UV ratio, and [{\rm O\, {\small III}}] equivalent widths, and that predicted by theoretical models, suggest burstier star-formation histories and/or more heterogeneous metallicity and ionizing conditions in z\gt 7 galaxies. We report a rapid decline of the [{\rm O\, {\small III}}] luminosity density at z\gtrsim 6\!-\!7 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 ~ 10-20{{\ \rm per\ cent}} of the ionizing budget at z=7\!-\!8 (assuming an escape fraction of 10{{\ \rm per\ cent}}), raising the prospect of directly detecting a significant fraction of the sources of reionization with JWST.
