EPOCHS IX. When cosmic dawn breaks: Evidence for evolved stellar populations in $7 < z < 12$ galaxies from PEARLS GTO and public NIRCam imaging

Understand

The presence of evolved stars in high-redshift galaxies can place valuable indirect constraints on the onset of star formation in the Universe.

• Thus we use PEARLS GTO and public NIRCam photometric data to search for Balmer-break candidate galaxies at $7 < z < 12$.
• We find that our Balmer-break candidates at $z \sim 10.5$ tend to be older (115 Myr), have lower inferred [O III] + H$\beta$ emission line equivalent widths (120 \r{A}), have lower specific star formation rates (6 Gyr$^{-1}$) and redder UV slopes ($\beta = -1.8$) than our control sample of galaxies.
• However, these trends all become less strong at $z \sim 8$, where the F444W filter now probes the strong rest-frame optical emission lines, thus providing additional constraints on the current star formation activity of these galaxies.