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, and we comment on the extent to which changing the scanning strategy
can mitigate the systematics. Most importantly, we show how systematics can be
disentangled from the intensity signal based on their spin properties via
map-making. We illustrate this 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.
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