2024A&A...691A.262K

Context. The Fred Young Submillimeter Telescope (FYST) line intensity mapping (LIM) survey will measure the power spectrum (PS) of the singly ionized carbon 158 μm fine-structure line, [CII], to trace the appearance of the first galaxies that emerged during and right after the epoch of reionization (EoR, 6 < z < 9).
Aims. We aim to quantify the contamination of the (post-)EoR [CII] LIM signal by foreground carbon monoxide (CO) line emission (3 < J_up < 12) and assess the efficiency to retrieve this [CII] LIM signal by the targeted masking of bright CO emitters.
Methods. Using the IllustrisTNG300 simulation, we produced mock CO intensity tomographies based on empirical star formation rate-to-CO luminosity relations. Combining these predictions with the [CII] PS predictions of the first paper of this series, we evaluated a masking technique where the interlopers are identified and masked using an external catalog whose properties are equivalent to those of a deep Euclid survey.
Results. Prior to masking, our [CII] PS forecast is an order of magnitude lower than the predicted CO contamination in the 225 GHz ([CII] emitted at z = 6.8 - 8.3) band of the FYST LIM survey, at the same level in its 280 GHz ([CII] emitted at z = 5.3 - 6.3) and 350 GHz ([CII] emitted at z = 4.1 - 4.8) bands, and an order of magnitude higher in its 410 GHz ([CII] emitted at z = 3.4 - 3.9) band. For our fiducial model, the optimal masking depth is reached when less than 10% of the survey volume is masked at 350 and 410 GHz but around 40% at 280 GHz and 60% at 225 GHz. At these masking depths we anticipate a detection of the [CII] PS at 350 and 410 GHz, a tentative detection at 280 GHz, whereas at 225 GHz the CO signal still dominates our model. In the last case, alternative decontamination techniques will be needed.