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 was marked by the formation of the first stars, and preceded
the Epoch of Reionization (EoR), when the Universe underwent a fundamental
transformation caused 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 (SKA) is envisaged to be
the largest and most sensitive radio telescope at metre and centimetre
wavelengths. The latest Aperture Array Verification Systems feature 7-m 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,
introducing chromatic aberrations into the instrument bandpass. This causes
power from the foreground signals to appear at higher delays, potentially
contaminating the ‘EoR window’, a region in 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 Galactic and
Extragalactic All-Sky MWA (GLEAM) Survey, Haslam $408,$MHz, and a 1.5-cGpc
21-cm brightness temperature cube generated with the 21cmSPACE simulator. 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 $leq 10, Omega$, the
reflection is confined below the EoR window. However, we demonstrate that even
a 0.1 per cent length tolerance introduces contamination with an absolute
fractional difference of $sim 10$ per cent across all accessible k-modes.
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