Affiliation: Cosmic DAWN Center

Contribution: Oral

Title: COSMOS-Web: stellar mass assembly in connection to dark matter halos in 13.4 Gyr of cosmic history

Abstract: We use the largest contiguous area of ∼ 0.5 deg2 imaged by JWST from the COSMOS-Web survey to study the stellar mass assembly in the largest redshift range to date, 0.2 < z < 12, by measuring the galaxy stellar mass function (SMF) in 15 redshift bins. The unprecedented wide-area imaging by JWST/NIRCam, in combination with the wealth of ancillary data from both ground and space in COSMOS, allows us to probe the evolution of some of the most massive and rarest objects at all epochs. We do a careful rest-frame optical based sample selection and remove sources that host potential active galactic nuclei (AGN) that can lead to biased stellar mass estimates. We fit our measurements with double and single Schecter as well as double power law functions, and use these to measure the cosmic stellar mass density (SMD) and indirectly infer the cosmic star formation rate density (SFRD). We make the connection to dark matter halos by performing abundance matching to estimate the stellar-to-halo mass relation (SHMR) at 0.2 < z < 12 for the first time consistently in such a large redshift range. We find increased abundances of massive galaxies, confirming indications from previous JWST studies. The SMF shows a transition from a Schechter function to a double power law at z ∼ 6, coinciding with the onset of negative AGN feedback. Our analysis of the SHMR allows us to quantify the evolution of the integrated star formation efficiency (SFE), confirming its strong dependence on mass (both halo and stellar). The SFE shows that after little evolution out to z ∼ 4, it starts to quickly increase with redshift and reach close to 100% efficiency for the highest masses. We interpret our results by comparing to several simulations and theoretical models and find that simulations fail to predict the increased abundances of massive galaxies at z > 7. Our measurements show remarkable consistency with the predictions of the Feedback-Free Bursts (FFB) model but suggest that the maximum SFE in the FFB regime increases with both redshift and mass. On the other hand, the transition from a Schecter to a double power law as well as the monotonic increase of the SFE at z ∼ 6 with mass are qualitatively consistent with the positive feedback from AGN in the early Universe, proposed to explain the JWST observations of abundant populations of massive galaxies and AGN in the early Universe. This work presents the most comprehensive measurements of the stellar mass function and the stellar mass density at 0.2 < z < 12 that provide the next-generation benchmark for galaxy formation models and simulation.

This contribution can be found here (pdf).