University of Groningen
Large-scale 21-cm Cosmology with LOFAR and AARTFAAC Gehlot, Bharat Kumar
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Publication date: 2019
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Gehlot, B. K. (2019). Large-scale 21-cm Cosmology with LOFAR and AARTFAAC. University of Groningen.
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Propositions
accompanying the dissertation
Large-scale 21-cm Cosmology with LOFAR and AARTFAAC
1. To detect the faint 21-cm signal of hydrogen from the Cosmic Dawn, the most cru-cial hurdles to overcome are the removal of the bright partly-polarised foregrounds, the ionospheric and instrumental errors, and their interplay. (Chapter 2,3,4,5)
2. Nearly all 21-cm signal contaminants are more severe in ‘low-frequency’ Cosmic Dawn experiments than in ‘high-frequency’ EoR experiments. (Chapter 2)
3. Instrumental-polarisation leakage of bright unpolarised sources away from the zenith produces signatures in delay-baseline space similar to that of polarised foregrounds. (Chapter 2)
4. Ionospheric diffractive scales towards sources far from the zenith can be as small as hun-dreds of meters at low frequencies, contaminating part of the 21-cm signal space with scintillation noise. (Chapter 2)
5. Imposing frequency smoothness on direction independent and dependent receiver gains during calibration significantly improves the overall calibration process. (Chapter 3) 6. Statistical foreground removal techniques, such as Gaussian Process Regression (GPR),
are the proper way forward in 21-cm experiments. (Chapter 3,4)
7. An accurate estimate of the noise bias is hard to achieve but also essential for measuring the power spectrum of the 21-cm signal. (Chapter 3,4)
8. The 21-cm brightness temperature power spectrum is below (14 K)2 at k =
0.038hMpc−1in the redshift rangez= 20 − 25. (Chapter 3)
9. A hybrid foreground modelling approach that combines multi-scale clean and shapelet decomposition is needed to produce a foreground model for calibration which encodes information on all relevant spatial scales. (Chapter 5)
10. All-sky imaging instruments require innovative image representations and combina-tions on a sphere rather than on a plane. (Chapter 4,5)
11. The combined intellectual effort between different experiments around the globe is re-quired to detect the cosmological 21-cm signal.
12. It is vital to have flexible daily working hours to achieve maximum productivity and results.
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