Spin-based removal of instrumental systematics in 21cm intensity mapping surveys

TL;DR

This paper introduces a formalism leveraging scan strategy and spin symmetry to model, disentangle, and reduce instrumental systematics, especially polarization leakage, in 21cm intensity mapping surveys, improving signal recovery.

Contribution

The paper presents a novel formalism that uses spin properties and scan strategy information to model and mitigate instrumental systematics in 21cm intensity mapping.

Findings

Formalism classifies systematics by spin symmetry.

Method can disentangle systematics from the intensity signal.

Approach effectively reduces contamination from instrumental effects.

Abstract

Upcoming cosmological intensity mapping surveys will open new windows on the Universe, but they must first overcome a number of significant systematic effects, including polarization leakage. We present a formalism that uses scan strategy information to model the effect of different instrumental systematics on the recovered cosmological intensity signal for `single-dish' (autocorrelation) surveys. This modelling classifies different systematics according to their spin symmetry, making it particularly relevant for dealing with polarization leakage. We show how to use this formalism to calculate the expected contamination from different systematics as a function of the scanning strategy. Most importantly, we show how systematics can be disentangled from the intensity signal based on their spin properties via map-making. We illustrate this, using a set of toy models, for some simple instrumental systematics, demonstrating the ability to significantly reduce the contamination to the observed intensity signal. Crucially, unlike existing foreground removal techniques, this approach works for signals that are non-smooth in frequency, e.g. polarized foregrounds. These map-making approaches are simple to apply and represent an orthogonal and complementary approach to existing techniques for removing systematics from upcoming 21cm intensity mapping surveys.