A Comprehensive Study of Galaxies at z ∼9-16 Found in the Early JWST Data: Ultraviolet Luminosity Functions and Cosmic Star Formation History at the Pre-reionization Epoch

We conduct a comprehensive study on dropout galaxy candidates at z similar to 9-16 using the first 90 arcmin(2) James Webb Space Telescope (JWST) Near Infrared Camera images taken by the early release observations (ERO) and early release science programs. With the JWST simulation images, we find that a number of foreground interlopers are selected with a weak photo-z determination (Delta chi(2) > 4). We thus carefully apply a secure photo-z selection criterion (Delta chi(2) > 9) and conventional color criteria with confirmations of the ERO Near Infrared Spectrograph spectroscopic redshifts, and obtain a total of 23 dropout galaxies at z similar to 9-16, including two candidates at and . We perform thorough comparisons of dropout galaxies found in our work with recent JWST studies, and conclude that our galaxy sample is reliable enough for statistical analyses. We derive the UV luminosity functions at z similar to 9-16, and confirm that our UV luminosity functions at z similar to 9 and 12 agree with those determined by other Hubble Space Telescope and JWST studies. The cosmic star formation rate (SFR) density decreases from z similar to 9 to 12, and perhaps to 16, but the densities at z similar to 12-16 are higher than the constant star formation efficiency model. Interestingly, there are six bright galaxy candidates at z similar to 10-16 with M-UV < -19.5 mag and M-* similar to 10(8-9)M(circle dot). Because a majority (similar to 80%) of these galaxies show no signatures of active galactic nuclei in their morphologies, the high cosmic SFR densities and the existence of these UV-luminous galaxies are explained by the lack of suppression of star formation by the UV background radiation at the pre-reionization epoch and/or an efficient UV radiation production by a top-heavy initial mass function with Population III-like star formation.

Automated summary

We conducted a comprehensive study on dropout galaxy candidates at z similar to 9-16 using the JWST's early release observations. We applied secure photo-z selection criteria and obtained 23 dropout galaxies. Our galaxy sample is reliable for statistical analyses and we derived the UV luminosity functions at z similar to 9-16. The study revealed high cosmic star formation rates and the existence of UV-luminous galaxies, suggesting the lack of suppression of star formation at the pre-reionization epoch.