The C-Band All Sky Survey (C-BASS):Observing diffuse Galactic emission at 5 GHz.

  • Melis Irfan

Student thesis: Phd


ABSTRACT OF THESIS submitted by Melis Omer Irfan for the Degree of Doctor of Philosophy and entitled The C-Band All Sky Survey (C-BASS): Observing diffuse Galactic emission at 5 GHz. June 2014. University of Manchester.Measurements of the diffuse Galactic emission are used for both the interpretation of sensitive cosmic microwave background data and the understanding of our Galaxy. I examine the diffuse Galactic emission at a central frequency of 4.76 GHz using data from the C-Band All-Sky Survey (C-BASS). The technical work presented here fo- cuses on microphonic oscillation mitigation, receiver noise measurements and radio frequency interference detection. Northern C-BASS is a continuous comparison ra- diometer with a system temperature of 40 K, a knee frequency of 0.10 mHz in polari- sation and a noise level of 2 mK sqrt(s). A calibration scheme was devised, using astro- nomical calibrators, to convert the data to Kelvin and correct for atmospheric opacity. This scheme is stable to 1 % over several months and accurate to better than 5 %. A major systematic in the C-BASS data is ground emission. In this work the ground emission is modelled and subtracted from the data resulting. A first scientific anal- ysis of C-BASS Northern intensity data was made to investigate the contributions of free-free and synchrotron emission within the Galactic plane. The synchrotron spectral index was determined to be -2.63±0.07 between 0.408 and 4.76 GHz and -2.71±0.14 between 1.420 and 4.76 GHz and the ratio of free-free to synchrotron emission at 4.76 GHz was found to be 53± 8 % to 47± 8 %. Bringing in higher frequency data allowed for the detection of anomalous microwave emission associated with W43, W44 and W47 at a level of 4.9sigma, 6.0sigma and 3.4sigma, respectively and demonstrated the need for C-BASS data to constrain the spectral form of AME within certain regions.
Date of Award1 Aug 2014
Original languageEnglish
Awarding Institution
  • The University of Manchester
SupervisorClive Dickinson (Supervisor)

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