Prospects for detecting C II emission during the epoch of reionization

We produce simulations of the atomic C ii line emission in large sky fields in order to determine the current and future prospects for mapping this line during the high-redshift epoch of reionization. We calculate the C ii line intensity, redshift evolution, and spatial fluctuations using observational relations between C ii emission and the galaxy star formation rate over the frequency range 200–300 GHz. We estimate an averaged intensity of $I_{CII}=(4\pm 2)\times {10}^{2}Jy{sr}^{-1}$ in the redshift range $z\sim 5.3-8.5$. Observations of the C ii emission in this frequency range will suffer contamination from emission lines at lower redshifts, in particular CO rotational lines. Using simulations, we estimated the CO contamination to be $I_{CO}\approx {10}^{3}Jy{sr}^{-1}$ (originating from galaxies at $z<2.5$). Using detailed simulations of the C ii and CO emission across a range of redshifts, we generate maps as a function of angle and frequency, fully taking into account this resolution and light-cone effects. In order to reduce the foreground contamination, we find that we should mask galaxies below redshifts ∼2.5 with a CO(J:2–1) to CO(J:6–5) line flux density higher than $5\times {10}^{-22}W{m}^{-2}$ or an AB magnitude lower than $m_K=22$. We estimate that the additional continuum contamination originating in emission from stars and in dust, free–free, free–bound, and two-photon emission in the interstellar medium is of the order of ${10}^{5}Jy{sr}^{-1}$, which is well above the expected C ii signal. We also consider the possibility of cross-correlating foreground lines with galaxy surveys in order to probe the intensity of the foregrounds. Finally, we discuss the expected constraints from two experiments capable of measuring the expected C ii power spectrum.