CEERS Key Paper. I. An Early Look into the First 500 Myr of Galaxy Formation with JWST

We present an investigation into the first 500 Myr of galaxy evolution from the Cosmic Evolution Early Release Science (CEERS) survey. CEERS, one of 13 JWST ERS programs, targets galaxy formation from z similar to 0.5 to >10 using several imaging and spectroscopic modes. We make use of the first epoch of CEERS NIRCam imaging, spanning 35.5 arcmin(2), to search for candidate galaxies at z > 9. Following a detailed data reduction process implementing several custom steps to produce high-quality reduced images, we perform multiband photometry across seven NIRCam broad- and medium-band (and six Hubble broadband) filters focusing on robust colors and accurate total fluxes. We measure photometric redshifts and devise a robust set of selection criteria to identify a sample of 26 galaxy candidates at z similar to 9-16. These objects are compact with a median half-light radius of similar to 0.5 kpc. We present an early estimate of the z similar to 11 rest-frame ultraviolet (UV) luminosity function, finding that the number density of galaxies at M (UV) similar to -20 appears to evolve very little from z similar to 9 to 11. We also find that the abundance (surface density [arcmin(-2)]) of our candidates exceeds nearly all theoretical predictions. We explore potential implications, including that at z > 10, star formation may be dominated by top-heavy initial mass functions, which would result in an increased ratio of UV light per unit halo mass, though a complete lack of dust attenuation and/or changing star formation physics may also play a role. While spectroscopic confirmation of these sources is urgently required, our results suggest that the deeper views to come with JWST should yield prolific samples of ultrahigh-redshift galaxies with which to further explore these conclusions.

Automated summary

We conducted an investigation into the first 500 million years of galaxy evolution using the CEERS survey. By analyzing the CEERS NIRCam imaging data, we identified a sample of 26 galaxy candidates at z similar to 9-16, suggesting that the number density of galaxies at this redshift range remains relatively constant. These findings highlight the potential of JWST to discover more ultrahigh-redshift galaxies in the future.