Resolving ambiguities in the inferred star formation histories of intense [O iii] emitters in the reionization Era

Early JWST spectroscopic campaigns have confirmed the presence of strong [O III ] line-emitting galaxies in the redshift interval 7 < z < 9. Although deduced earlier from Spitzer photometry as an indicative of young stellar populations, some studies suggested the rele v ant photometric excesses attributed to [O III ] emission could, in part, be due to Balmer breaks arising from older stars. We demonstrate that this is likely the case by exploiting medium-band near-infrared JWST photometry in the Hubble Ultra Deep Field. We locate a sample of six galaxies with redshifts 8.2

Automated summary

Early JWST spectroscopic campaigns have confirmed the presence of strong [O III] line-emitting galaxies in the redshift interval 7 < z < 9. Some studies have suggested that the photometric excesses attributed to [O III] emission could be caused by Balmer breaks from older stars. By utilizing medium-band near-infrared JWST photometry in the Hubble Ultra Deep Field, we have located six galaxies with redshifts 8.2, supporting the possibility of older stars causing the observed photometric excesses.