Affiliation: Scuola Normale Superiore Pisa

Contribution: Oral

Title: A shining cosmic dawn

Abstract: The advent of JWST is a giant leap forward in our understanding of the early Universe and the origin of the first galaxy populations at z>10. One of the most exciting and puzzling results is the discovery of numerous luminous galaxies already in place 300-500 Myrs after the Big Bang. Indeed, the cosmic number density of bright (M_uv<-20) candidate galaxies at z>10 is up to one order of magnitude higher than what was expected based on both pre-JWST observations and cosmological simulations. Such observations have raised several questions about the formation of such bright galaxies. Here we discuss the recent JWST observations of the most distant luminous galaxies spectroscopically confirmed at z~14. Both galaxies display a clear break in the flux density, with no flux detected blueward of 1.85 µm; the sharpness of which can only be explained as a Lyman-α break. These two galaxies have a Muv of −20.81 and −19 and provide a crisp spectroscopic confirmation to the trend that has been inferred several times from photometric samples that the galaxy UV luminosity function evolves slowly, with more luminous galaxies at high redshift than predicted. Thanks to the analysis of the size and the UV slope we conclude that the rest-frame UV emission is dominated by light of the stellar population and does not arise from an AGN. Despite the deep observations, the NIRSpec spectra do not yet detect any UV emission lines. This is in contrast to the observations of other luminous galaxies at low redshift. We thus discuss some possible models that address the lack of UV line and the existence of such large and luminous galaxies so early in cosmic history.

This contribution can be found here (pdf).