Abstract
We present measurements of the rest-frame ultraviolet luminosity function (UV
LF) at redshifts $z=3$, $z=4$ and $z=5$, using 96894, 38655 and 7571 sources
respectively to map the transition between AGN and galaxy-dominated ultraviolet
emission shortly after the epoch of reionization. Sources are selected using a
comprehensive photometric redshift approach, using $10$\ds\, of deep
extragalactic legacy fields covered by both HSC and VISTA. The use of template
fitting spanning a wavelength range of $0.3--2.4m$ achieves
$80--90$ per cent completeness, much higher than classical colour-colour
cut methodology. The measured LF encompasses $-26<M_UV<-19.25(-20.5)$ at
$z=3(5)$. This is further extended to $-28.5<M_UV<-16$ using
complementary results from other studies, allowing for the simultaneous fitting
of the combined AGN and galaxy LF. We find that there are fewer UV luminous
galaxies ($M_UV<-22$) at $z\sim3$ than $z\sim4$, indicative of an onset
of widespread quenching alongside dust obscuration, and that the evolution of
the AGN LF is much more rapid than the galaxy LF, with their number density
rising by around 2 orders of magnitude from $3<z<6$. We also find that it
remains difficult to determine if a double power law (DPL) functional form is
preferred over the Schechter function to describe the galaxy UV LF with
photometric data alone. Estimating the Hydrogen ionizing photon budget from our
UV LFs, we find that AGN can contribute to, but cannot solely maintain, the
reionization of the Universe at $z=3-5$. However, the rapidly evolving AGN LF
strongly disfavours a significant contribution within the EoR.
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