Affiliation: Université de Genève

Contribution: Oral

Title: The Stellar Mass Function in the first 1.5 Gyr of Cosmic History with JWST: Rapid Build-Up of Dust-Obscured Giants at z~4-5

Abstract: With its unprecedented sensitivity at wavelengths from 1-5 microns, the James Webb Space Telescope (JWST) has opened a new window on the rest-frame optical emission of galaxies at z>3, enabling us to perform a complete census of the galaxy population at z~4-9. Combining multiple public NIRCam imaging programs with ancillary data from HST, spanning a total area of ~500 arcmin^2, we compile a sample of >30,000 galaxies at these redshifts. We measure galaxy stellar mass functions (SMFs) at z~4-9 and show that they are broadly consistent with existing literature results. However, we find a rapid evolution of the high-mass end of the SMF from z~5 to z~4 which is entirely driven by UV-red galaxies that were largely missing from HST-based LBG samples. This points to a rapid build-up of massive dust obscured as well as quiescent galaxies in this redshift range. The total galaxy mass density grows by a factor ~25x in the ~1 Gyr of cosmic time from z~9 to z~4. Driven by rather high number densities at z~8 and at z~9 compared to previous literature results, this growth is slow from z~9 to z~7. It speeds up at later times due to the steeply rising contribution of UV-red galaxies, so that they dominate the cosmic stellar mass density above 10^8 solar masses at z~4. Our results emphasize the importance of rest-optical selected samples in inferring accurate physical properties and studying the mass build-up of galaxies in the first 1.5 Gyr of cosmic history.

This contribution can be found here (pdf).