• Christopher Tibbs

Student thesis: Phd


Cosmic Microwave Background (CMB) anisotropy measurements have provided a great insight to the cosmological parameters that define our Universe. Obtaining these measurements to ever higher sensitivity is complicated by the presence of contaminating foregrounds, whose physical understanding is, therefore, critical. The discovery of a dust-correlated emission mechanism in the frequency range 10 - 100 GHz, known an anomalous microwave emission, has reignited the study of Galactic foregrounds as interstellar medium (ISM) emission mechanisms. This thesis describes the investigation of this anomalous microwave emission, with the aim of improving our understanding of the physical processes causing this emission. Understanding the precise nature and spectral behaviour of this anomalous microwave emission is of critical importance for modelling Galactic foregrounds for current and future sensitive CMB anisotropy experiments (e.g. Planck).Very Small Array (VSA) observations of the dust feature, G159.6-18.5, in the Perseus molecular complex are presented. These observations were reduced and calibrated resulting in the production of a 33 GHz map of the region with ≈7 arcmin angular resolution and an r.m.s. noise level of < 20 mJy/beam. Five dust-correlated features were identified in this map, and the emission in these five features was found to be in excess over the standard Galactic emission processes of free-free and thermal vibrational dust emission, at a level of 2.5 - 5.6sigma. This excess of emission, in combination with the dust correlation, was interpreted as anomalous emission. Various theories have been proposed to explain this anomalous emission, however, evidence is provided showing that the only plausible explanation, consistent with the results found in G159.6-18.5, is that of electric dipole radiation from rapidly spinning dust grains i.e. spinning dust. Intriguingly, the bulk of this spinning dust emission (> 88 %) appears to be originating from a large-scale, diffuse component, and is not concentrated in the five compact components.Having detected this anomalous emission, which is consistent with the spinning dust hypothesis, photometric Spitzer data were completely reprocessed and used in conjunction with the dust emission model, DUSTEM, to characterise the dust within the region. The results of this dust characterisation are presented and were found to tentatively agree with the spinning dust hypothesis.Finally, this work provides evidence illustrating that anomalous emission is a very complex process, and that further work still needs to be performed.
Date of Award31 Dec 2010
Original languageEnglish
Awarding Institution
  • The University of Manchester
SupervisorRichard Davis (Supervisor)

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