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$\alpha$ at $z=7$, and CII 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$\alpha$ it is quite
possible to remove most of the foreground contribution from the maps via only
1%-3% pixel masking. The CII 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.
