The foreground wedge and 21 cm BAO surveys
Hee-Jong Seo, Christopher M. Hirata

TL;DR
This paper investigates how foreground contamination, known as the wedge effect, impacts the precision of cosmological measurements from 21 cm intensity mapping surveys, emphasizing the importance of calibration techniques to mitigate this issue.
Contribution
It quantifies the detrimental impact of the foreground wedge on BAO measurements at redshifts 1-2 and highlights the need for calibration methods to improve survey accuracy.
Findings
Wedge effect increases errors on angular diameter distances by 3-4.4 times.
Errors on H(z) increase by a factor of 1.5-1.6 due to the wedge.
Calibration techniques to remove the wedge are crucial for accurate 21 cm BAO surveys.
Abstract
Redshifted H{\sc\,i} 21 cm emission from unresolved low-redshift large scale structure is a promising window for ground-based Baryon Acoustic Oscillations (BAO) observations. A major challenge for this method is separating the cosmic signal from the foregrounds of Galactic and extra-Galactic origins that are stronger by many orders of magnitude than the former. The smooth frequency spectrum expected for the foregrounds would nominally contaminate only very small modes; however the chromatic response of the telescope antenna pattern at this wavelength to the foreground introduces non-smooth structure, pervasively contaminating the cosmic signal over the physical scales of our interest. Such contamination defines a wedged volume in Fourier space around the transverse modes that is inaccessible for the cosmic signal. In this paper, we test the effect of this contaminated…
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