Early results from GLASS-JWST. XI: Stellar masses and mass-to-light ratio of z>7 galaxies

P. Santini, A. Fontana, M. Castellano, N. Leethochawalit, M. Trenti, T. Treu, D. Belfiori, S. Birrer, A. Bonchi, E. Merlin, C. Mason, T. Morishita, M. Nonino, D. Paris, G. Polenta, P. Rosati, L. Yang, M. Bradac, A. Calabrò, A. Dressler, K. Glazebrook, D. Marchesini, S. Mascia, T. Nanayakkara, L. Pentericci, G. Roberts-Borsani, C. Scarlata, B. Vulcani, Xin Wang

Published 2022-07-22Version 1

We exploit James Webb Space Telescope (JWST) NIRCam observations from the GLASS-JWST-Early Release Science program, to investigate galaxy stellar masses at z>7. We first show that JWST observations reduce the uncertainties on the stellar mass by a factor 5-10, when compared with the highest quality data sets available to date. We then study the UV mass-to-light ratio, finding that galaxies exhibit a wide range of $M/L_{UV}$ values for a given luminosity, indicative of a broad variety of physical conditions and star formation histories. As a consequence, previous estimates of the cosmic star stellar mass density - based on an average correlation between UV luminosity and stellar mass - can be biased by as much as a factor of 6. Our first exploration demonstrates that JWST represents a new era in our understanding of stellar masses at z>7, and therefore of the growth of galaxies prior to cosmic reionization.