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

Abstract: 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~0.5 to z>10 using several imaging and spectroscopic modes. We make use of the first epoch of CEERS NIRCam imaging, spanning 35.5 sq. arcmin, 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 multi-band 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~9-16. These objects are compact with a median half-light radius of ~0.5 kpc. We present an early estimate of the z~11 rest-frame ultraviolet (UV) luminosity function, finding that the number density of galaxies at M_UV ~ -20 appears to evolve very little from z~9 to z~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 ultra-high-redshift galaxies with which to further explore these conclusions.

An Exploration of Early Galaxy Formation with JWST: Findings from CEERS

This study presents an investigation of the first 500 million years of galaxy formation, as reported in the Cosmic Evolution Early Release Science (CEERS) survey. Utilizing the James Webb Space Telescope (JWST), the CEERS survey probes the evolution of galaxies from redshifts ( z \sim 0.5 ) to ( z > 10 ) using imaging and spectroscopic methods. The research particularly focuses on identifying candidate galaxies at ( z > 9 ) with the NIRCam imaging from the first epoch, covering an area of 35.5 square arcminutes.

The authors employ several custom data reduction steps to ensure high-quality imaging, followed by multi-band photometry across six Hubble Space Telescope (HST) broadband filters and seven NIRCam filters. The paper details the identification of 26 galaxy candidates at ( 9 \leq z \leq 16 ), characterized by their compact nature, with a median half-light radius of approximately 0.5 kpc. A significant finding is the determination of an early estimate of the ( z \sim 11 ) rest-frame ultraviolet (UV) luminosity function, suggesting minimal evolution in the number density of galaxies at ( M_{UV} \sim -20 ) from ( z \sim 9 ) to ( z \sim 11 ).

Contrary to theoretical predictions, the observed abundance of these galaxy candidates is higher than expected. The paper explores the implications of this, suggesting that star formation at ( z > 10 ) may be influenced by a top-heavy initial mass function (IMF), which could boost the UV light output per unit halo mass. A reduced level of dust attenuation or altered star-formation physics may also contribute to this observed excess.

While the paper acknowledges the urgent need for spectroscopic confirmation of these sources, it posits that future deeper observations with JWST will likely yield large samples of ultra-high-redshift galaxies. Such observations will be crucial to further dissecting these early findings and refining our understanding of galaxy formation in the nascent universe.

This study has profound implications for cosmology and early universe research, particularly in exploring the physics of star formation and galaxy evolution at the highest redshifts. As JWST continues to provide new insights, these findings hint at potentially transformative developments in understanding the universe’s infancy. Future research should focus on establishing spectroscopic confirmations, exploring the potential impact of IMF variations at these redshifts, and examining the interplay between galaxy formation and cosmic reionization.