UV and 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 ~ 3

Abstract

We constrain the rest-frame FUV (1546 Å), NUV (2345 Å), and U-band (3690 Å) luminosity functions (LFs) and luminosity densities (LDs) with unprecedented precision from z ~ 0.2 to z ~ 3 (FUV, NUV) and z ~ 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 MFUV, MNUV, MU ≃ -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 ~ 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 ~ 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, while at z > 1 it is due to the evolution of both M∗UV and the characteristic number density φ∗UV. In contrast, the U-band LF has an excess of faint galaxies and is fitted with a double-Schechter form; M∗U, both φ∗U 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.