The UV and Ly$α$ Luminosity Functions of galaxies and the Star Formation Rate Density at the end of HI reionization from the VIMOS Ultra-Deep Survey (VUDS)

Y. Khusanova, O. Le Fèvre, P. Cassata, O. Cucciati, B. C. Lemaux, L. A. M. Tasca, R. Thomas, B. Garilli, V. Le Brun, D. Maccagni, L. Pentericci, G. Zamorani, R. Amorín, S. Bardelli, M. Castellano, L. P. Cassarà, A. Cimatti, M. Giavalisco, N. P. Hathi, O. Ilbert, A. M. Koekemoer, F. Marchi, J. Pforr, B. Ribeiro, D. Schaerer, L. Tresse, D. Vergani, E. Zucca

Published 2019-03-05Version 1

We establish a robust statistical description of the star-forming galaxy population at the end of cosmic HI reionization ($5.0\le{}z\le6.6$) from a large sample of 52 galaxies with spectroscopically confirmed redshifts from the VIMOS UltraDeep Survey. We identify galaxies with Ly$\alpha$ either in absorption or in emission, at variance with most spectroscopic samples in the literature where Ly$\alpha$ emitters dominate. We find that star-forming galaxies at these redshifts are distributed along a main sequence in the stellar mass vs. SFR plane. We report a flat evolution of the sSFR(z) in 3<z<6 compared to lower redshift measurements. UV-continuum slopes vary with luminosity, with a large dispersion. We determing UV and Ly$\alpha$ luminosity functions using V$_{max}$ method and use them to derive star formation rate densities (SFRD). We find that both UV-derived and Ly$\alpha$-derived SFRDs are in excellent agreement after correcting Ly$\alpha$ luminosity density for IGM absorption. Our new SFRD measurements at a mean redshift z=5.6 confirm the steep decline of the SFRD at z>2. The bright end of the Ly$\alpha$ luminosity function has a high number density, indicating a significant star formation activity concentrated in the brightest Ly$\alpha$ emitters (LAE) at these redshifts. LAE with EW>25\AA ~contribute to about 75\% of the total UV-derived SFRD. While our analysis favors a low dust content in 5.0<z<6.6, uncertainties on the dust extinction correction and associated degeneracies in spectral fitting will remain an issue to estimate the total SFRD until future survey extending spectroscopy to the NIR rest-frame spectral domain, e.g. with JWST.