On the ages of bright galaxies $\sim 500$ Myr after the Big Bang: insights into star formation activity at $z \gtrsim 15$ with JWST

Understand

With JWST, new opportunities to study the evolution of galaxies in the early Universe are emerging.

• Spitzer constraints on rest-optical properties of $z\gtrsim7$ galaxies demonstrated the power of using galaxy stellar masses and star formation histories (SFHs) to indirectly infer the cosmic star formation history.
• However, only the brightest individual $z\gtrsim8$ objects could be detected with Spitzer, making it difficult to robustly constrain activity at $z\gtrsim10$.
• Here, we leverage the greatly improved rest-optical sensitivity of JWST at $z\gtrsim8$ to constrain the ages of seven UV-bright ($M_{UV}\lesssim-19.5$) galaxies selected to lie at $z\sim8.5-11$, then investigate implications for $z\gtrsim15$ star formation.