A ${\bf 1.4}$ deg${\bf ^2}$ blind survey for CII], CIII] and CIV at
  ${\bf z\sim0.7-1.5}$. II: luminosity functions and cosmic average line ratios
  Recently, the CIII] and CIV emission lines have been observed in galaxies in
the early Universe ($z>5$), providing new ways to measure their redshift and
study their stellar populations and AGN. We explore the first blind CII], CIII]
and CIV survey ($z\sim0.68, 1.05, 1.53$, respectively) presented in Stroe et
al. (2017). We derive luminosity functions (LF) and study properties of CII],
CIII] and CIV line emitters through comparisons to the LFs of H$\alpha$ and
Ly$\alpha$ emitters, UV selected star forming (SF) galaxies and quasars at
similar redshifts. The CII] LF at $z\sim0.68$ is equally well described by a
Schechter or a power-law LF, characteristic of a mixture of SF and AGN
activity. The CIII] LF ($z\sim1.05$) is consistent to a scaled down version of
the Schechter H$\alpha$ and Ly$\alpha$ LF at their redshift, indicating a SF
origin. In stark contrast, the CIV LF at $z\sim1.53$ is well fit by a
power-law, quasar-like LF. We find that the brightest UV sources ($M_{UV}<-22$)
will universally have CIII] and CIV emission. However, on average, CIII] and
CIV are not as abundant as H$\alpha$ or Ly$\alpha$ emitters at the same
redshift, with cosmic average ratios of $\sim0.02-0.06$ to H$\alpha$ and
$\sim0.01-0.1$ to intrinsic Ly$\alpha$. We predict that the CIII] and CIV lines
can only be truly competitive in confirming high redshift candidates when the
hosts are intrinsically bright and the effective Ly$\alpha$ escape fraction is
below 1 per cent. While CIII] and CIV were proposed as good tracers of young,
relatively low-metallicity galaxies typical of the early Universe, we find
that, at least at $z\sim1.5$, CIV is exclusively hosted by AGN/quasars,
especially at large line equivalent widths.
