Initial exploration of 21-cm cosmology with imaging and power spectra from the Murchison Widefield Array

Abstract

The Murchison Widefield Array (MWA) is a new low-frequency radio array under construction in Western Australia with a primary goal of measuring the power spectrum of the 21-cm signal from neutral hydrogen during the Epoch of Reionization (EoR). In this thesis, we detail efforts to characterize the MWA system, and present scientific results from a 32-element prototype interferometer deployed at the MWA site. We develop simulations and perform anechoic chamber measurements to verify the performance of the MWA antenna tiles. We develop a calibration and imaging pipeline for the MWA which uses w-projection widefield imaging techniques and direction-dependent point spread functions. Using data from an MWA expedition in March 2010, we produce confusion-limited maps covering ~ 2700 square degrees in a region of sky with low galactic temperature. We develop a blind source detection and extraction algorithm, and use it to perform a blind survey in these maps, and detect 655 sources at high significance with an additional 871 candidates. We compare these sources with existing low-frequency radio surveys in order to assess the MWA-32T system performance, and to identify new candidates for ultra-steep spectrum radio sources. In order to constrain the EoR, we apply two power spectrum estimation techniques to this dataset: a Fast Fourier Transform in order to rapidly compute power spectra, and a quadratic estimation method which uses inverse covariance weighting to produce an optimal estimate. We use a principal component analysis to identify and remove the foreground contaminants. In the resulting two-dimensional power spectra, we find the predicted "wedge" feature due to the chromaticity of the instrumental response, and identify a sensitive region free of strong contaminants which can be used for characterizing the EoR signal. We then use these data to produce new limits on the EoR power spectrum at z = 9.