Towards optimal foreground mitigation strategies for interferometric H I intensity mapping in the low-redshift Universe

We conduct the first case study towards developing optimal foreground mitigation strategies for neutral hydrogen (H I) intensity mapping using radio interferometers at low redshifts. A pipeline for simulation, foreground mitigation, and power spectrum estimation is built, which can be used for ongoing and future surveys using MeerKAT and Square Kilometre Array Observatory. It simulates realistic sky signals to generate visibility data-given instrument and observation specifications, which is subsequently used to perform foreground mitigation and power spectrum estimation. A quadratic estimator formalism is developed to estimate the temperature power spectrum in visibility space. Using MeerKAT telescope specifications for observations in the redshift range, z ∼ 0.25–0.30, corresponding to the MeerKAT International GHz Tiered Extragalactic Exploration (MIGHTEE) survey, we present a case study, where we compare different approaches of foreground mitigation. We find that component separation in visibility space provides a more accurate estimation of H I clustering when compared with foreground avoidance, with the uncertainties being 30 per cent smaller. Power spectrum estimation from image is found to be less robust with larger bias and more information loss when compared with estimation in visibility. We conclude that for the considered sub-band of z ∼ 0.25–0.30, the MIGHTEE survey will be capable of measuring the H I power spectrum from k ∼ 0.5 to k ∼ 10 Mpc⁻¹ with signal-to-noise ratio being ∼3. We are the first to show that, at low redshift, component separation in visibility space suppresses foreground contamination at large line-of-sight scales, allowing measurement of H I power spectrum closer to the foreground wedge, crucial for data analysis towards future detections.