Exploring star formation in galaxy populations using the far-infrared - radio correlation

In this thesis I take a close look at the far-infrared radio - correlation, a puzzlingly persistent and tight relationship identified between the far-infrared and radio luminosities of star forming galaxies. Two disparate processes are attributed to this phenomenon. In the first, starlight from massive stars is reprocessed by dust to be re-emitted in the infrared and secondly, radio emission in the form of synchrotron radiation originating in shocks driven by these same high mass stars as they end their lives as supernovae. Cosmic ray electrons are accelerated by these shocks, their paths subsequently spiralling in their host galaxies magnetic fields, produce a continuum of synchrotron radiation. I investigate this far-infrared radio correlation for a large sample of IRAS galaxies and compare my results to previous studies. I look at the effect of peak galaxy dust temperature on the correlation, dividing my sample into ‘warm’ and ‘cool’ bins and find a lower flux ratio in the warm sample. The correlation at low radio frequencies is tested, probing the constancy of the dominant synchrotron radiation where absorption or other effects are expected to lead to a divergence from the linear continuum spectrum. Finally I look at a smaller sample of galaxies in the ELAIS-N1 field using HerMES and GMRT data to investigate the correlation to higher redshifts. The interest and rational for investigating this correlation is its evident link to star formation. Any deviation for example will imply an evolution in one or both of these processes which are closely linked to star formation. With the advent of new dedicated low frequency array radio telescopes such as LOFAR it is increasingly necessary to trust the correlation at these longer wavelengths if observational data is to be used as a reliable predictive tool in the study of star formation.