Kavli Affiliate: Kiyoshi Masui
| First 5 Authors: Haochen Wang, Kiyoshi Masui, Kevin Bandura, Arnab Chakraborty, Matt Dobbs
| Summary:
The main challenge of 21 cm cosmology experiments is astrophysical
foregrounds which are difficult to separate from the signal due to telescope
systematics. An earlier study has shown that foreground residuals induced by
antenna gain errors can be estimated and subtracted using the hybrid foreground
residual subtraction (HyFoReS) technique which relies on cross-correlating
linearly filtered data. In this paper, we apply a similar technique to the
CHIME stacking analysis to subtract beam-induced foreground contamination.
Using a linear high-pass delay filter for foreground suppression, the CHIME
collaboration reported a $11.1sigma$ detection in the 21 cm signal stacked on
eBOSS quasar locations, despite foreground residual contamination mostly due to
the instrument chromatic transfer function. We cross-correlate the
foreground-dominated data at low delay with the contaminated signal at high
delay to estimate residual foregrounds and subtract them from the signal. We
find foreground residual subtraction can improve the signal-to-noise ratio of
the stacked 21 cm signal by $ 10 – 20%$ after the delay foreground filter,
although some of the improvement can also be achieved with an alternative
flagging technique. We have shown that it is possible to use HyFoReS to reduce
beam-induced foreground contamination, benefiting the analysis of the HI auto
power spectrum with CHIME and enabling the recovery of large scale modes.
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