Star formation histories of UV-luminous galaxies at $z \simeq 6.8$: implications for stellar mass assembly at early cosmic times

Understand

The variety of star formation histories (SFHs) of $z\gtrsim6$ galaxies provides important insights into early star formation, but has been difficult to systematically quantify.

• Some observations suggest that many $z\sim6-9$ galaxies are dominated by $\gtrsim200$ Myr stellar populations, implying significant star formation at $z\gtrsim9$, while others find that most reionization era galaxies are $\lesssim10$ Myr, consistent with little $z\gtrsim9$ star formation.
• Here, we quantify the distribution of ages of UV-bright ($-22.5\lesssim M_{UV}\lesssim-21$) galaxies colour-selected to lie at $z\simeq6.6-6.9$, an ideal redshift range to systematically study the SFHs of reionization era galaxies with ground-based observatories and Spitzer.
• We infer galaxy properties with two SED modelling codes and compare results, finding that stellar masses are largely insensitive to the model, but the inferred ages can vary by an order of magnitude.