Speaker
Description
Measurement of the 21 cm emission of neutral hydrogen in the intergalactic medium probes the era of the first luminous objects and the era of the intergalactic medium becoming fully ionized by the first stars, the Epoch of Reionization (EoR). However, the 21 cm signal is orders of magnitude fainter than astrophysical foregrounds, as well as other sources of radio frequency interference, making it challenging to measure. It is therefore imperative that any instrumental systematic effects which could further distort spectral structure are properly understood and mitigated. Kolopanis (2023) identified a systematic in Phase II data from the MWA which manifests as excess power. This introduces a bias that can make foregrounds couple into 21cm background modes. One possible explanation for such an effect is mutual coupling between antennas. We have built an electromagnetic software simulation of the antenna beam using FEKO to estimate the amplitude of this effect for the MWA. We have modeled multiple MWA tiles, in different orientations to study the resulting beam pattern. FEKO calculates coupling coefficients, which can be compared to an approximate model of mutual coupling accounting only for re-radiation. We find that the mutual coupling coefficient predicted by both methods is on a similar level as sensitivity of the deepest available power spectrum limits. This means that, while the mutual coupling we predict is much smaller than the systematic observed by Kolopanis et al, it is potentially brighter than forecast sensitivity limits. Further work is necessary to make more detailed predictions but the conclusion as limits are improved, mutual coupling will need to be accounted for.
| Timeslot preferences | 30min |
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