Studying high-z galaxies with [C II] intensity mapping

We investigate the [C II] line intensity mapping (IM) signal from galaxies in the Epoch of Reionization (EoR) to assess its detectability, the possibility to constrain the LC II-SFR relation, and to recover the [C II] luminosity function (LF) from future experiments. By empirically assuming that log LC II = log A + γ SFR ± σL, we derive the [C II] LF from the observed UV LF, and the [C II] IM power spectrum. We study the shot noise and the full power spectrum separately. Although, in general, the shot-noise component has a much higher signal-to-noise ratio than the clustering one, it cannot be used to put independent constraints on log A and γ . Full power spectrum measurements are crucial to break such degeneracy and reconstruct the [C II] LF. In our fiducial survey S1 (inspired by CCAT-p/1000 h) at z ∼ 6, the shot-noise (clustering) signal is detectable for two (one) of the five considered LC II-SFR relations. The shot noise is generally dominated by galaxies with LC II > 108-109 L☉ (MUV ∼ −20 to −22), already at reach of ALMA pointed observations. However, given the small field of view of such telescope, an IM experiment would provide unique information on the bright end of the LF. The detection depth of an IM experiment crucially depends on the (poorly constrained) LC II-SFR relation in the EoR. If the LC II-SFR relation varies in a wide log A-γ range, but still consistent with ALMA [C II] LF upper limits, even the signal from galaxies with LC II as faint as ∼107 L☉ could be detectable. Finally, we consider the contamination by continuum foregrounds (cosmic infrared background, dust, cosmic microwave background) and CO interloping lines, and derive the requirements on the residual contamination level to reliably extract the [C II] signal.