  We present a search for CII emission over cosmological scales at
high-redshifts. The CII line is a prime candidate to be a tracer of star
formation over large-scale structure since it is one of the brightest emission
lines from galaxies. Redshifted CII emission appears in the submillimeter
regime, meaning it could potentially be present in the higher frequency
intensity data from the Planck satellite used to measure the cosmic infrared
background (CIB). We search for CII emission over redshifts z=2-3.2 in the
Planck 545 GHz intensity map by cross-correlating the 3 highest frequency
Planck maps with spectroscopic quasars and CMASS galaxies from the Sloan
Digital Sky Survey III (SDSS-III), which we then use to jointly fit for CII
intensity, CIB parameters, and thermal Sunyaev-Zeldovich (SZ) emission. We
report a measurement of an anomalous emission
$\mathrm{I_\nu}=6.6^{+5.0}_{-4.8}\times10^4$ Jy/sr at 95% confidence, which
could be explained by CII emission, favoring collisional excitation models of
CII emission that tend to be more optimistic than models based on CII
luminosity scaling relations from local measurements; however, a comparison of
Bayesian information criteria reveal that this model and the CIB & SZ only
model are equally plausible. Thus, more sensitive measurements will be needed
to confirm the existence of large-scale CII emission at high redshifts.
Finally, we forecast that intensity maps from Planck cross-correlated with
quasars from the Dark Energy Spectroscopic Instrument (DESI) would increase our
sensitivity to CII emission by a factor of 5, while the proposed Primordial
Inflation Explorer (PIXIE) could increase the sensitivity further.
