Measuring ultralarge scale effects in the presence of 21cm intensity mapping foregrounds

Hi intensity mapping will provide maps of the large-scale distribution of neutral hydrogen (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 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(NL) and GR effects) with the residual foregrounds. We conclude that a joint analysis does not provide a catastrophic degradation of constraints and provides a framework to determine the marginal errors of large scale-effects in the presence of foregrounds. Similarly, we conclude that the macroscopical properties of the foregrounds can be measured with high precision. Notwithstanding, such results are highly dependent on accurate forward modelling of the foregrounds, which incorrectly done catastrophically bias the best-fitting values of cosmological parameters, foreground parametrizations, and large-scale effects.

Automated summary

High intensity mapping provides maps of the large-scale distribution of neutral hydrogen in the universe, which can be used to constrain primordial non-Gaussianity and test Einstein's theory of gravity. Foreground contamination is a challenge, but joint analysis does not severely degrade constraints and can help measure the macroscopical properties of foregrounds accurately.