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 $z \sim 3$
  We constrain the rest-frame FUV (1546\AA), NUV (2345\AA) and U-band (3690\AA)
luminosity functions (LFs) and luminosity densities (LDs) with unprecedented
precision from $z\sim0.2$ to $z\sim3$ (FUV, NUV) and $z\sim2$ (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 $z\sim2$.
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 $z\sim1$, 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, $M^\star_{UV}$, while at $z>1$ it is due to the
evolution of both $M^\star_{UV}$ and the characteristic number density
$\phi^\star_{UV}$. In contrast, the U-band LF has an excess of faint galaxies
and is fitted with a double-Schechter form; $M^\star_\mathrm{U}$, both
$\phi^\star_\mathrm{U}$ 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.
