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Title: Stars, gas, and dust at high resolution in the triangulum galaxy
Author: Williams, Thomas George
ISNI:       0000 0004 8500 7868
Awarding Body: Cardiff University
Current Institution: Cardiff University
Date of Award: 2019
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This thesis investigates the interplay between dust, gas, and stars at high resolution in nearby Local Group galaxy M33. Using panchromatic spectral energy distribution (SED) fitting along with ancillary gas tracer data, the star formation law is studied at scales of 100pc. A strong scale dependence is seen in the fitted power law index no matter which gas tracer is used, and whilst correlations between each tracer of gas and SFR remain strong, the correlation between SFR and molecular gas is strongest, perhaps indicating that the molecular gas is the more important driver of star formation. A catalogue of Giant Molecular Clouds (GMCs) is extracted from sub-millimetre wavelength data. These clouds have a much lower gas-to-dust ratio (GDR) than found in the Milky Way. The mass function of these clouds follows a slope proportional to M⁻².⁸⁴, implying that M33 is poorer at forming massive clouds than other nearby spirals. This study finds no absence of massive clouds at large galactocentric radius as in earlier CO studies, perhaps indicating a population of CO-dark gas dominated clouds at these larger distances. I also find that these clouds generally have masses several times larger than their virial mass, indicating that they are dominated by gravitational forces. A high-resolution, radiative transfer model for M33 is constructed from inputted maps of stellar and dust geometries. This simple model well fits the observed SED from UV to sub-millimetre wavelengths. In terms of stellar attenuation by dust, a reasonably strong, broad UV bump is found, as well as significant systematic differences in the amount of dust attenuation when compared to standard SED modelling. There are discrepancies in the residuals of the spiral arms versus the diffuse interstellar medium (ISM), indicating a difference in properties between these two regimes. Dust heating is dominated by unevolved stellar populations at all wavelengths. The dust-energy balance is restored at spatial scales greater than around 1.5kpc.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QB Astronomy