The C-Band All Sky Survey: Towards a complete analysis of the Northern Survey

UoM administered thesis: Phd

  • Authors:
  • Adam Barr

Abstract

Observations of diffuse Galactic emission are important, both for studies of the Galactic interstellar medium (ISM) and for precise measurements of the properties of the cosmic microwave background. The C-Band All Sky Survey (C-BASS) aims to make well-calibrated, high sensitivity full-sky maps at 5 GHz frequency. I have quantified and improved the measurement of the ground spillover, the largest systematic remaining in C-BASS data, using simulations and jackknives. The ground spillover is removed using ground templates produced by averaging the observed signal into azimuth bins at constant elevations. The ground templates align well with the terrain around the telescope, and are stable to within 10%. The ground signal was reduced to a typical rms level of 100 microkelvin in intensity and 50 microkelvin in polarisation. The residual ground signal is 1% of the high-latitude sky signal on large angular scales (l < 30). The anomalous microwave emission (AME) from Galactic sources was studied, with the Planck Collaboration et al. (2014b) catalogue being reassessed using C-BASS data and an MCMC fitter. Three new strongly significant (sigma_AME > 5) and eleven new semisignificant (5 > sigma_AME > 2) were identified, while three semi-significant Planck sources were found to have no significant AME. The results are consistent with spinning dust emission. An anti-correlation was found between the AME fraction and the strength of the interstellar radiation field, G0, with a best-fitting power-law gradient of = -0.64 +/- 0.10. A positive correlation was found between the AME emissivity and G0, which suggests that the distribution of grain sizes are changing. The SED of M31 was measured, with no significant AME being detected. Instead, the spectra is dominated by synchrotron and free-free emission. However, the contribution from extra-galactic sources has not been fully quantified, and this may change the result. Five low emissivity, high significance AME sources were examined. G166.44-24.08 (Pleiades Cluster) was found to be associated with a reflection nebula surrounding a B type star, with a strong radiation field (G0 of 9.4). The remaining four sources were associated with cold dust surrounding young stellar objects, and have weak radiation field (G0 < 0.55). This is because the weak radiation field is failing to excite the dust population, reducing the AME emissivity.

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Original languageEnglish
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Award date1 Aug 2021