Measurements of diffuse galactic emission at 5 GHz with C-BASS

Thesis

The C-Band All-Sky Survey (C-BASS) is a project to produce an all-sky map in intensity and polarization at a central frequency of 5 GHz with 1 GHz bandwidth and approximately 1 degree resolution. The central frequency is low enough for the map to be dominated by synchrotron and free-free emission but high enough so that Faraday rotation and depolarization are small across most of the sky. The C-BASS map will enable a more accurate removal of contaminating foregrounds from measurements of the cosmic microwave background, particularly in polarization where the B-mode signal from inflation is likely to be orders of magnitude weaker than the diffuse Galactic foreground emission.

To produce an all-sky map from the ground requires two telescopes, one in the northern and one in the southern hemisphere. This thesis focuses on analysis of C-BASS North data.

The noise properties of time-ordered data are characterised by fitting a noise model to periodograms. Using simulations, the errors introduced into the C-BASS maps by a destriping mapmaker are quantified and we reduce the signal error by masking the brightest pixels during baseline offset estimation. Jackknife tests are used to test the C-BASS data for systematics and to test the accuracy of the sensitivity maps. In total intensity, the spectral index of diffuse Galactic emission between 5 GHz and 408 MHz is measured using an extended T-T plot method and the results are compared to simulations. The spectral index of polarized diffuse Galactic emission between 5 GHz and 30 GHz is estimated in 55 arcminute pixels, modelling the polarized intensity as a Rician random variable.

Authors: Jew, L

• DOI: 10.5287/ora-zbrgngnnx
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: Diffuse Galactic emission; Noise properties; Foregrounds; Mapmaking; CMB
• Subjects: Synchrotron radiation; Radio astronomy; Astrophysics; Radio telescopes; Cosmic background radiation