Abstract
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.
Description
[1704.01124] 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
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