UV & U-band luminosity functions from CLAUDS and HSC-SSP -- I. Using four million galaxies to simultaneously constrain the very faint and bright regimes to $z\sim 3$

Abstract

We constrain the rest-frame FUV (1546à ), NUV (2345à ) and U-band (3690à ) luminosity functions (LFs) and luminosity densities (LDs) with unprecedented precision from $z\sim 0.2$ to $z\sim 3$ (FUV, NUV) and $z\sim 2$ (U-band). Our sample of over 4.3 million galaxies, selected from the CFHT Large Area $U$-band Deep Survey (CLAUDS) and HyperSuprime-Cam Subaru Strategic Program (HSC-SSP) data lets us probe the very faint regime (down to $M_{\mathrm{FUV}},M_{\mathrm{NUV}},M_{\mathrm{U}}\simeq -15$ at low redshift) while simultaneously detecting very rare galaxies at the bright end down to comoving densities $<10^{-5}$ Mpc${}^{-3}$. Our FUV and NUV LFs are well fitted by single Schechter functions, with faint-end slopes that are very stable up to $z\sim 2$. We confirm, but self-consistently and with much better precision than previous studies, that the LDs at all three wavelengths increase rapidly with lookback time to $z\sim 1$, and then much more slowly at $1<z<2$--$3$. Evolution of the FUV and NUV LFs and LDs at $z<1$ is driven almost entirely by the fading of the characteristic magnitude, $M_{UV}^{\star }$, while at $z>1$ it is due to the evolution of both $M_{UV}^{\star }$ and the characteristic number density $\ddot{I}{•}_{UV}^{\star }$. In contrast, the U-band LF has an excess of faint galaxies and is fitted with a double-Schechter form; $M_{\mathrm{U}}^{\star }$, both $\ddot{I}{•}_{\mathrm{U}}^{\star }$ components, and the bright-end slope evolve throughout $0.2<z<2$, while the faint-end slope is constant over at least the measurable $0.05<z<0.6$. We present tables of our Schechter parameters and LD measurements that can be used for testing theoretical galaxy evolution models and forecasting future observations.

18 pages, 11 figures (26 pages, 18 figures including the Appendix). Accepted for publication in MNRAS. Version to be published