- Title
- Observations of cosmic re-ionisation with the Hydrogen Epoch of Reionization Array: simulations of closure phase spectra
- Creator
- Charles, Ntsikelelo
- ThesisAdvisor
- Smirnov, OA
- ThesisAdvisor
- Bernardi, G
- ThesisAdvisor
- Bester, L
- Subject
- Epoch of reionization
- Subject
- Space interferometry
- Subject
- Astronomy -- Observations
- Subject
- Closure phase spectra
- Date
- 2021-04
- Type
- thesis
- Type
- text
- Type
- Masters
- Type
- MSc
- Identifier
- http://hdl.handle.net/10962/174470
- Identifier
- vital:42480
- Description
- The 21 cm transition from neutral Hydrogen promises to be the best observational probe of the Epoch of Reionisation. It has driven the construction of the new generation of low frequency radio interferometric arrays, including the Hydrogen Epoch of Reionization Array (HERA). The main difficulty in measuring the 21 cm signal is the presence of bright foregrounds that require very accurate interferometric calibration. Thyagarajan et al. (2018) proposed the use of closure phase quantities as a means to detect the 21 cm signal, which has the advantage of being independent (to first order) from calibration errors and therefore, bypasses the need for accurate calibration. Closure phases are, however, affected by so-called direction dependent effects, e.g. the fact that the dishes - or antennas - of an interferometric array are not identical to each other and , therefore, yield different antenna primary beam responses. In this thesis, we investigate the impact of direction dependent effects on closure quantities and simulate the impact that primary antenna beams affected by mutual coupling have on the foreground closure phase and its power spectrum i.e. the power spectrum of the bispectrum phase (Thyagarajan et al., 2020). Our simulations show that primary beams affected by mutual coupling lead to an overall leakage of foreground power in the so-called EoR window, i.e. power from smooth-spectrum foregrounds is confined to low k modes. We quantified this effect and found that the leakage is up to ~ 8 orders magnitude higher than the case of an ideal beam at kǁ > 0:5 h Mpc-1. We also found that the foreground leakage is worse when edge antennas are included, as they have a more different primary beam compared to antennas at the centre of the array. The leakage magnitude is worse when bright foregrounds appear in the antenna sidelobes, as expected. Our simulations provide a useful framework to interpret observations and assess which power spectrum region is expected to be most contaminated by foreground power leakage.
- Format
- computer, online resource, application/pdf, 1 online resource (101 pages), pdf
- Publisher
- Rhodes University, Faculty of Science, Physics and Electronics
- Language
- English
- Rights
- Charles, Ntsikelelo
- Rights
- All Rights Reserved
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| Thumbnail | File | Description | Size | Format | |||
|---|---|---|---|---|---|---|---|
| View Details | SOURCE1 | CHARLES-MSC-TR21-83.pdf | 2 MB | Adobe Acrobat PDF | View Details |