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Höfer, Carolin

University of British Columbia

The Canadian Hydrogen Intensity Mapping Experiment (CHIME) is a drift-scan radio telescope designed to map large-scale structure in the universe using the redshifted 21 cm line emitted by neutral hydrogen. By observing the 400 MHz to 800 MHz frequency band, CHIME will measure the expansion rate of the universe in the redshift range z = 0.8 – 2.5 to constrain the nature of dark energy. In this frequency range, astrophysical foregrounds from the Galaxy and extragalactic point sources are much brighter than the 21 cm emission. This requires aggressive foreground filtering. We developed a new implementation of the Karhunen-Loeve transform that correctly tracks the signal and noise power in our data to enable us to filter bright foregrounds. Moreover, we significantly improved the foreground model by modelling the point source sky component based on source count models for both the clustered and Poisson distributed sources with a parameterized maximum flux density cut for point sources which have not been explicitly subtracted from the data. The data volumes for CHIME are extremely large, therefore we developed an upgraded parallelized power spectrum estimation pipeline which is able to forecast the Fisher information matrix and estimate power spectra for three times the frequency range and five times the number of unique baselines by distributing the power spectrum bands across nodes. This allows us to scale the Monte-Carlo simulations to arrays almost as large as CHIME. Due to the bright astrophysical foregrounds CHIME has very stringent calibration requirements. We wrote an end-to-end simulation pipeline and studied various realistic sources of calibration uncertainties with it. The calibration requirements are very stringent and CHIME currently does not quite meet the requirements when using the Karhunen-Loeve foreground filter. We investigated different processing choices on power spectrum estimation with CHIME data in the 610 MHz to 680 MHz band with a selection of short baselines to ensure quick computation times. Even with our currently best calibration procedures our power spectrum estimates are several orders of magnitude higher than the expected from the 21 cm signal. Using a delay filter as an intermediate processing step reduces the power further.

Text

2022-08-26

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/82545

Physics

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/