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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: 10/23/2024 7:08:11 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 significantly depend on the rest-UV andrest-optical brightness of these sources. In short, our work confirms thatphotometry alone has the potential to measure BB strengths and to identifyevolved stellar populations at high redshift and that such objects may be morefrequent than previously thought. The presence of galaxies with a range ofbreak strengths and the joint presence of BB and emission lines indicate abursty nature of the star formation in the early Universe.