[CII] line intensity mapping the epoch of reionization with the Prime-Cam on FYST. I. Line intensity mapping predictions using the Illustris TNG hydrodynamical simulation

Aims: We predict the three-dimensional intensity power spectrum (PS) of the [CII] 158 μm line throughout the epoch of (and post) reionization at redshifts from ≈3.5 to 8. We study the detectability of the PS in a line intensity mapping (LIM) survey with the Prime-Cam spectral-imager on the Fred Young Submillimeter Telescope (FYST).
Methods: We created mock [CII] tomographic scans in redshift bins at z ≈ 3.7, 4.3, 5.8, and 7.4 using the Illustris TNG300-1 ΛCDM simulation and adopting a relation between the star formation activity and the [CII] luminosity (L_[CII]) of galaxies. A star formation rate (SFR) was assigned to a dark matter halo in the Illustris simulation in two ways: (i) we adopted the SFR computed in the Illustris simulation and, (ii) we matched the abundance of the halos with the SFR traced by the observed dust-corrected ultraviolet luminosity function of high-redshift galaxies. The L_[CII] is related to the SFR from a semi-analytic model of galaxy formation, from a hydrodynamical simulation of a high-redshift galaxy, or from a high-redshift [CII] galaxy survey. The [CII] intensity PS was computed from mock tomographic scans to assess its detectability with the anticipated observational capability of the FYST.
Results: The amplitude of the predicted [CII] intensity power spectrum varies by more than a factor of 10, depending on the choice of the halo-to-galaxy SFR and the SFR-to-L_[CII] relations. In the planned 4° ×4° FYST LIM survey, we expect a detection of the [CII] PS up to z ≈ 5.8, and potentially even up to z ≈ 7.4. The design of the envisioned FYST LIM survey enables a PS measurement not only in small (< 10 Mpc) shot noise-dominated scales, but also in large (> 50 Mpc) clustering-dominated scales making it the first LIM experiment that will place constraints on the SFR-to-L_[CII] and the halo-to-galaxy SFR relations simultaneously.