A panchromatic study of the stellar population and dust content of nearby galaxies

This thesis mainly focuses on the dust content in nearby galaxies, whilst also probing the underlying stellar populations. Our main target is the nearby starburst galaxy M82. Five additional nearby galaxies are included in the final chapter. Using NUV and optical photometry, along with FUV, Hα and 8µ data, we explore the radial dependence of the dust properties. We model the dust attenuation law using a prescription that parameterises the total-to-selective extinction ratio (RV ) and NUV bump strength (B). We also include the colour excess as a parameter describing the amount of dust. By comparing with stellar population synthesis models, we show that it is possible to marginalise over nuisance parameters such as the age or metallicity of the populations. We find a significant radial trend of the dust-related properties both in M82 and the other galaxies, although there is a large variance of this trend among them. Remarkably, we find that M82s data does not match the “Calzetti” attenuation law (applied to starburst galaxies). In fact the analysis favours a law with a significant NUV bump. As a function of radius, we find that B and RV decrease outwards, with a Milky-Way like behaviour in the central region and a steeper (lower RV ) wavelength dependence in the outer regions. We explore this trend in the other five galaxies, finding a large variation in the radial trends from galaxy to galaxy, revealing the complexity of the dust properties