Epoch of Reionization Foreground Removal

Abstract

We present a new simulation for generating radio sky maps: 21cmPASSIVE (21cmPretty Awesome Sky Simulator; It's Very Excellent). The purpose of the simulationis to predict the contribution of radio point-like sources, specifically distant radiogalaxies, to the total sky emission. The simulation shows that radio point sourcesare the dominant contaminant in the final maps. Sky maps are created based on theparameters of the Square Kilometre Array (SKA), and therefore the maps emulatewhat we expect SKA data to look like. Using 21cmPASSIVE maps between redshifts6 and 13, we attempt to clean the point sources, and also explore masking brightsources. This is accomplished through the use of a blind detection method workingin the image plane. We find that subtracting sources appears to be efficient for thosedetected with a signal-to-noise (S/N) > 2. Source subtraction works better whenwe do not constrain the shape of the modelled sources to be equal to that of theinstrumental beam (in our case a circular Gaussian), but allow them to be fittedas ellipses. This better handles instances where nearby or overlapping sources canbe mistaken for a single elongated source due to confusion. The masking routinewas also applied for sources down to a limiting S/N > 2. The optimal mask sizeappears to be 2.5 times the radius of the detected sources. We also experimentedwith combinations of the subtracting and masking routines and find that, whenoptimized, these cleaning techniques succeeded in reducing the foreground powerspectrum down by between 1 and 2 orders of magnitude.

Date of Award	31 Dec 2016
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Michael Brown (Supervisor) & Anna Bonaldi (Supervisor)