LOFAR Epoch of Reionization: Statistical Methods & First Results
Until now, we have no observations of the time period when the first stars and galaxies were formed. Therefore, we have not been able to answer questions such as: when did the first stars form and what did they look like? The goal of my research is to answer these questions by studying radio waves emitted in the era of the formation of the first stars. This thesis presents techniques to detect these faint signals and some first results from observations with the LOFAR telescope in the Netherlands.
The expected radio signal is very faint compared to the noise in observations. It is thus not possible to make images of the signal. However, I show that we should be able to detect the signal by measuring the level of its fluctuations in space.
Galaxies nearby us are thousands of times brighter than the cosmic radio signal. I show that filtering these nearby galaxies from the observed data, based on our inadequate knowledge about them, can further enhance the noise. This realization has helped devising a new strategy to remove signals from nearby galaxies. A 13 hour observation with the LOFAR telescope was analysed with the new strategy, and we achieved a sensitivity to detect signals which are as faint as 80 millikelvin. The expected cosmic signal, however, is only about 5 millikelvin. The methods presented in this thesis are currently being used to analyse hundreds of hours of observations with the hope to detect the cosmic signal.