A 158 Micron [CII] Line Survey of Galaxies at z ~ 1 to 2: An Indicator
  of Star Formation in the Early Universe
  We have detected the 158 {\mu}m [CII] line from 12 galaxies at z~1-2. This is
the first survey of this important starformation tracer at redshifts covering
the epoch of maximum star-formation in the Universe and quadruples the number
of reported high z [CII] detections. The line is very luminous, between
<0.024-0.65% of the far-infrared continuum luminosity of our sources, and
arises from PDRs on molecular cloud surfaces. An exception is PKS 0215+015,
where half of the [CII] emission could arise from XDRs near the central AGN.
The L[CII] /LFIR ratio in our star-formation-dominated systems is ~8 times
larger than that of our AGN-dominated systems. Therefore this ratio selects for
star-formation-dominated systems. Furthermore, the L[CII]/LFIR and
L[CII]/L(CO(1-0)) ratios in our starforming galaxies and nearby starburst
galaxies are the same, so that luminous starforming galaxies at earlier epochs
(z~1-2) appear to be scaled up versions of local starbursts entailing
kilo-parsec-scale starbursts. Most of the FIR and [CII] radiation from our
AGN-dominated sample (excepting PKS 0215+015) also arises from kpc scale
starformation, but with far-UV radiation fields ~8 times more intense than in
our star-formation-dominated sample. We speculate that the onset of AGN
activity stimulates large-scale star-formation activity within AGN-dominated
systems. This idea is supported by the relatively strong [OIII] line emission,
indicating very young stars, that was recently observed in high z composite
AGN/starburst systems. Our results confirm the utility of the [CII] line, and
in particular, the L[CII]/L(FIR) and L[CII]/LCO(1-0) ratios as a tracers of
star-formation in galaxies at high redshifts.
