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: 3/13/2024 8:00:11 PM

Paper abstract: Combining the public JWST/NIRCam imaging programs CEERS, PRIMER and JADES,spanning a total area of ~500 arcmin^2, we obtain a sample of >30,000galaxies at z~4-9 that allows us to perform a complete, rest-opticalselected census of the galaxy population at z>3. Comparing the stellar massM_* and the UV-slope \beta distributions between JWST- and HST-selectedsamples, we generally find very good agreement and no significant biases.Nevertheless, JWST enables us to probe a small population of UV-red galaxiesthat was missing from previous HST-based LBG samples. We measure galaxy stellarmass functions (SMFs) at z~4-9 and show that they are broadly consistentwith existing literature results. However, UV-red galaxies dominate thehigh-mass end of the SMF at least out to z~6. In particular the mostmassive galaxies typically show very red colors between\lambda_{obs}~1.5\mum and ~4.5\mum, and thus JWST's unprecedentedresolution and sensitivity at these wavelengths yields more accurateconstraints on their abundance and masses. The implied redshift evolution ofthe high-mass end of the SMF suggests a rapid build-up of massive dust-obscuredas well as quiescent galaxies from z~6 to z~4 as well as an enhancedefficiency of star formation towards earlier times (z\gtrsim6). We find theSMFs to be steep over the entire redshift range, and slightly steepening withredshift from z~ 4-6, reaching values of ~-2 at z\gtrsim6.Finally, we show that the galaxy mass density grows by a factor ~20\timesin the ~1 Gyr of cosmic time 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.