Kavli Affiliate: George Efstathiou
| First 5 Authors: Oscar Sage David O’Hara, Fred Dulwich, Eloy de Lera Acedo, Jiten Dhandha, Thomas Gessey-Jones
| Summary:
The Cosmic Dawn marks the first star formations and preceded the
Epoch-of-Reionization, when the Universe underwent a fundamental transformation
propelled by the radiation from these first stars and galaxies. Interferometric
21-cm experiments aim to probe redshifted neutral hydrogen signals from these
periods, constraining the conditions of the early Universe. The SKA-LOW
instrument of the Square Kilometre Array telescope is envisaged to be the
largest and most sensitive radio telescope at m and cm wavelengths. The latest
Aperture Array Verification Systems feature 7m coaxial transmission lines
connecting the Low Noise Amplifiers to optical transmitters at the front of the
analogue-receiving chain. An impedance mismatch between these components
results in a partially reflected electromagnetic signal, which introduces
chromatic aberrations in the instrument bandpass. This causes power from the
foreground signals to appear at higher delays, potentially contaminating the
EoR window, a region at which the 21-cm signal should be detectable. We present
an end-to-end simulation pipeline for SKA-LOW using a composite sky model
combining radio foregrounds from The GLEAM Survey, Haslam $408$MHz, and a
$1.5$cGpc 21-cm brightness temperature cube generated with the 21cmSPACE
simulator. Iterating a parametric approach, we derive a model for the
scattering parameters of a coaxial transmission line in terms of its
specifications and bulk material properties. Assuming identical cables of
length $leq 15.0$m with impedance mismatch $leq 10Omega$ confines the
reflection to k-modes below the EoR window. However, we demonstrate that even a
$0.1$% length tolerance introduces contamination with an RMSE of $sim 10$%
across all accessible k-modes.
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