Kavli Affiliate: George Efstathiou
| First 5 Authors: Emma Shen, Dominic Anstey, Marta Spinelli, Eloy de Lera Acedo, Anastasia Fialkov
| Summary:
The precise measurement of the sky-averaged HI absorption signal between 50
and 200 MHz is the primary goal of global 21-cm cosmology. This measurement has
the potential to unravel the underlying physics of cosmic structure formation
and evolution during the Cosmic Dawn. It is, however, hindered by various
non-smooth, frequency-dependent effects, whose structures resemble those of the
signal. One such effect is the leakage of polarised foregrounds into the
measured intensity signal: polarised foreground emission undergoes Faraday
rotation as it passes through the magnetic fields of the interstellar medium,
imprinting a chromatic structure in the relevant frequency range which
complicates the extraction of the cosmological HI absorption feature. We
investigate the effect of polarised Galactic foregrounds on extracting the
global 21-cm signal from simulated data using REACH’s data analysis pipeline;
the Radio Experiment for the Analysis of Cosmic Hydrogen (REACH) is an
experiment designed to detect the sky-averaged 21-cm HI signal from the early
Universe using physically informed models. Using the REACH pipeline, we
successfully recover an injected global 21-cm signal with an amplitude of
approximately 0.16 K, centred between 80 and 120 MHz, achieving a low
root-mean-square error (less than 30% of the injected signal strength) in all
the tested cases. This includes scenarios with simulated polarised Galactic
diffuse emissions and polarised point source emissions, provided the overall
polarisation fraction is below $sim 3%$. The linear mixing of contamination,
caused by the superposition of multiple patches with varying strengths of
Faraday rotation, produces patterns that are more distinct from the global
signal. This distinction makes global signal recovery easier compared to
contamination resulting from a single, slow oscillation pattern.
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