Physical properties of galaxies and the UV Luminosity Function from $z\sim 6$ to $z\sim 14$ in COSMOS-Web

Abstract

We present measurements of the rest-frame ultraviolet luminosity function (UVLF) in three redshift bins over $z\sim 5.5$-14 from the JWST COSMOS-Web survey. Our samples, selected using the dropout technique in the HST/ACS F814W, JWST/NIRCam F115W, and F150W filters, contain a total of 3099 galaxies spanning a wide luminosity range from faint ($M_{\mathrm{UV}}\sim -19$ mag) to bright ($M_{\mathrm{UV}}\sim -22.5$ mag). The galaxies are undergoing rapid star formation, with blue stellar populations. Surprisingly, their median UV spectral slope ${\hat{I}}^2$ does not evolve at $z>8$, suggesting minimal dust, or physical separation of dust and star formation at early epochs. The measured UVLF exhibits an excess at the bright-end ($M_{\mathrm{UV}}<-21$ mag) compared to pre-JWST empirical results and theoretical predictions of an evolving Schechter function, with the excess beginning at $z\sim 9$ and becoming increasingly prominent toward $z\sim 12$. Our analysis suggests that reproducing the observed abundance of UV-bright galaxies at high redshift requires a combination of physical processes, including elevated star formation efficiencies, moderate levels of stochasticity in galaxy luminosities, and minimal dust attenuation.

35 pages, 17 figures, submitted to ApJ