Hydrogen intensity mapping with MeerKAT: Preserving cosmological signal by optimising contaminant separation

Abstract

Removing contaminants is a delicate, yet crucial step in neutral hydrogen (HI) intensity mapping and often considered the technique's greatest challenge. Here, we address this challenge by analysing HI intensity maps of about $100$ deg${}^2$ at redshift $z\approx 0.4$ collected by the MeerKAT radio telescope, an SKA Observatory (SKAO) precursor, with a combined 10.5-hour observation. Using unsupervised statistical methods, we removed the contaminating foreground emission and systematically tested, step-by-step, some common pre-processing choices to facilitate the cleaning process. We also introduced and tested a novel multiscale approach: the data were redundantly decomposed into subsets referring to different spatial scales (large and small), where the cleaning procedure was performed independently. We confirm the detection of the HI cosmological signal in cross-correlation with an ancillary galactic data set, without the need to correct for signal loss. In the best set-up we achieved, we were able to constrain the HI distribution through the combination of its cosmic abundance (${\Omega }_{HI}$) and linear clustering bias ($b_{HI}$) up to a cross-correlation coefficient ($r$). We measured ${\Omega }_{HI}{b}_{HI}r=[0.93\pm 0.17]\times 10^{-3}$ with a $\approx 6\sigma$ confidence, which is independent of scale cuts at both edges of the probed scale range ($0.04\lesssim k\lesssim 0.3h$ Mpc${}^{-1}$), corroborating its robustness. Our new pipeline has successfully found an optimal compromise in separating contaminants without incurring a catastrophic signal loss. This development instills an added degree of confidence in the outstanding science we can deliver with MeerKAT on the path towards HI intensity mapping surveys with the full SKAO.

Summary of results in Table 1 and Figure 16 on page 15. This version matches the one accepted for publication

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