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

Abstract

ABSTRACT 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 $L_{\rm C\,{\small II}}\!-\!{\rm SFR}$ relation, and to recover the [C ii] luminosity function (LF) from future experiments. By empirically assuming that ${\rm log}\,L_{\rm C\,{\small II}}={\rm log}\,A+\gamma {\rm SFR}\pm \sigma _\mathrm{ L}$, 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 $L_{\rm C\,{\small II}}\!-\!{\rm SFR}$ relations. The shot noise is generally dominated by galaxies with $L_{\rm C\,{\small II}}\gtrsim 10^{8}\!-\!10^{9}~ \mathrm{L}_\odot$ (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) $L_{\rm C\,{\small II}}\!-\!{\rm SFR}$ relation in the EoR. If the $L_{\rm C\,{\small II}}\!-\!{\rm SFR}$ 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 $L_{\rm C\,{\small II}}$ 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.