Predictions and sensitivity forecasts for reionization-era [C II] line intensity mapping

Observations of the high-redshift Universe using the 21 cm line of neutral hydrogen and complimentary emission lines from the first galaxies promise to open a new door for our understanding of the epoch of reionization. We present predictions for the [C II] 158 μm line and H I 21 cm emission from redshifts z = 6-9 using high-dynamic-range cosmological simulations combined with semi-analytical models. We find that the CONCERTO experiment should be able to marginally detect the large-scale power spectrum of [C II] emission to redshifts of up to z = 8 (signal-to-noise ratio ∼1 at k < 0.1 h cMpc^-1 with 1500 h of integration). A Stage II experiment similar to CCAT-p should be able to detect [C II] from even higher redshifts to high significance for similar integration times (signal-to-noise ratio of ∼50 at k = 0.2 h cMpc^-1 at z = 6). We study the possibility of combining such future [C II] measurements with 21 cm measurements using LOFAR and SKA to measure the [C II]-21cm cross power spectra, and find that a Stage II experiment should be able to measure the cross power spectrum for k ≲ 1 h cMpc^-1 to signal-to-noise ratio of better than 10. We discuss the capability of such measurements to constrain astrophysical parameters relevant to reionization and show that a measurement of the [C II]-21cm cross power spectrum helps break the degeneracy between the mass and brightness of ionizing sources.