Early Results From GLASS-JWST. XVII: Building the First Galaxies -- Chapter 1. Star Formation Histories at 5<z < 7

A. Dressler, B. Vulcani, T. Treu, M. Rieke, C. Burns, A. Calabro', A. Bonchi, M. Castellano, A. Fontana, N. Leethochawalit, C. Mason, E. Merlin, T. Morishita, D. Paris, A. Mercurio, T. Nanayakkara, B. M. Poggianti, P. Santini, X. Wang, K. Misfelt, D. P. Stark, C. Wilmer

Published 2022-08-08Version 1

JWST observations of high redshift galaxies are used to measure their star formation histories -- the buildup of stellar mass in the earliest galaxies. A novel analysis program, SEDz*, compares near-IR spectral energy distributions for galaxies with redshift $5<z<7$ to combinations of stellar population templates evolved from $z=12$. We exploit NIRCam imaging in 7 wide bands covering $1-5\mu m$, taken in the context of the GLASS-JWST-ERS program, and use SEDz* to solve for well-constrained star formation histories for 24 exemplary galaxies in this redshift range. In this first look we find variety of histories, from long, continuous star formation over $5<z<12$, short but intense starbursts -- sometimes repeating, and, most commonly, contiguous, steady mass buildup lasting ~0.5 Myr, possibly the seeds of today's typical, M* galaxies.