Masking line foregrounds in intensity mapping surveys

TL;DR

This paper proposes a pixel masking method to reduce line foreground contamination in intensity mapping surveys, effectively recovering cosmological signals for CO and Lyα lines, with more challenges for CII.

Contribution

The study introduces a simple masking technique to mitigate line confusion in intensity mapping, demonstrating its effectiveness for certain lines using simulated data.

Findings

Masking 1-3% of brightest pixels removes most foregrounds for CO and Lyα.

CII maps are more difficult to clean due to higher foreground contamination.

Useful cosmological information can still be retrieved despite data masking.

Abstract

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.