James Webb Space Telescope Feed Post

Arxiv: Galaxy Build-up in the first 1.5 Gyr of Cosmic History: Insights from the Stellar Mass Function at z\sim4-9 from JWST NIRCam Observations Published: 3/13/2024 8:00:11 PM Updated: 9/9/2024 10:17:31 AM

Paper abstract: Combining the public JWST/NIRCam imaging programs CEERS, PRIMER and JADES,spanning a total area of ~500\,{\rm arcmin}^2, we obtain a sample of>30,000 galaxies at z_{\rm phot}~4-9 that allows us to perform acomplete, rest-optical selected census of the galaxy population at z>3.Comparing the stellar mass M_* and the UV-slope \beta distributions betweenJWST- and HST-selected samples, we generally find very good agreement and nosignificant biases. Nevertheless, JWST enables us to probe a new population ofUV-red galaxies that was missing from previous HST-based Lyman Break Galaxy(LBG) samples. We measure galaxy stellar mass functions (SMFs) at z~4-9down to limiting masses of 10^{7.5}-10^{8.5}\,{\rm M_\odot}, finding steeplow mass slopes over the entire redshift range, reaching values of\alpha~-2 at z\gtrsim6. At the high-mass end, UV-red galaxiesdominate at least out to z~6. The implied redshift evolution of the SMFsuggests a rapid build-up of massive dust-obscured or quiescent galaxies fromz~6 to z~4 as well as an enhanced efficiency of star formationtowards earlier times (z\gtrsim6). Finally, we show that the galaxy massdensity grows by a factor ~20\times from z~9 to z~4. Our resultsemphasize the importance of rest-frame optically-selected samples in inferringaccurate distributions of physical properties and studying the mass build-up ofgalaxies in the first 1.5 Gyr of cosmic history.