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Arxiv: Strong Balmer break objects at z ~ 7-10 uncovered with JWST Published: 7/24/2024 7:44:37 PM Updated: 7/24/2024 7:44:37 PM

Paper abstract: We report the discovery of robust spectroscopically confirmed Balmer break(BB) galaxies and candidates, with secure spectroscopic redshifts 7.1 \le z\le 9.6 from publicly available JWST extra-galactic photometric andspectroscopic surveys. To do so, we used dedicated filters probing the Balmerbreak and inspected the objects with NIRSpec spectroscopy. We recover thepreviously known objects with strong Balmer breaks and reveal 10-11 new objectswith clear BBs, thus tripling the number of spectroscopically confirmedgalaxies with a BB at z >7. Approximately half of them show a pure BB and nosigns of recent star formation, whereas the other half shows BB and emissionlines, indicating most likely galaxies whose star formation ceased earlier andhas restarted recently. Overall we find that ~10-20% of all galaxies from oursample show signatures of an evolved stellar population. Furthermore, we findthat the strength of the BB does not strongly depend on the rest-opticalbrightness of these sources. In short, our work confirms that photometry alonehas the potential to measure BB strengths and to identify evolved stellarpopulations at high redshift and that such objects may be more frequent thanpreviously thought.