Masking line foregrounds in intensity-mapping surveys

We address the problem of line confusion in intensity-mapping surveys and explore the possibility to mitigate line foreground contamination by progressively masking the brightest pixels in the observed map. We consider experiments targeting CO(1–0) at z = 3, Ly α at z = 7, and C ii at z = 7, and use simulated intensity maps, which include both clustering and shot-noise components of the signal and possible foregrounds, in order to test the efficiency of our method. We find that for CO and Ly α, it is quite possible to remove most of the foreground contribution from the maps via only 1–3 per cent pixel masking. The C ii maps will be more difficult to clean, however, due to instrumental constraints and the high-intensity foreground contamination involved. While the masking procedure sacrifices much of the astrophysical information present in our maps, we demonstrate that useful cosmological information in the targeted lines can be successfully retrieved.