Measuring ultra-large scale effects in the presence of 21cm intensity mapping foregrounds

Understand

\textsc{Hi} intensity mapping will provide maps of the large-scale distribution of neutral hydrogen (\textsc{Hi}) in the universe.

• These are prime candidates to be used to constrain primordial non-Gaussianity using the Large Scale Structure of the Universe as well as to provide further tests of Einstein's theory of Gravity (GR).
• But \textsc{Hi} maps are contaminated by foregrounds, which can be several orders of magnitude above the cosmological signal.
• Here we quantify how degenerated are the large-scale effects ($f_{\rm NL}$ and GR effects) with the residual foregrounds.