A Bayesian approach to the study of dark matter in disk galaxies

A Bayesian Approach to the Study of Dark Matter in Disk Galaxies by Peter R. Hague Studies of the rotation of disk galaxies have long been used to infer the presence and distribution of dark matter within them. Here I present a new Markov Chain Monte Carlo (MCMC) method to explore the extensive and complex parameter space created by the possible combinations of dark and luminous matter in these galaxies. I present exhaustive testing of this method to ensure it can retrieve dark matter halo parameters from artificial data, and apply it to real galaxies from The HI Nearby Galaxy Survey (THINGS) and other sources. The results of these studies can shed some light on how disk galaxies form and evolve. Chapters 1 and 2 provide background for the physics and statistical methods respectively. Chapter 3 shows the testing of the MCMC method on artificial data, and applies it to DDO 154 to find a more robust constraint on the inner log slope than previous methods. Chapter 4 applies this method to a broad range of galaxies taken from the THINGS survey, constrains their physical properties, and presents a simple model of feedback to compare with. Chapter 5 applies the method to M33, mapping a degeneracy between the log slope of the dark matter halo and the mass-to-light ratio, that excludes the combination of a cored halo and a light stellar disk. Chapter 6 extends the MCMC method to an earlier stage of analysis by marginalising over the parameter space of possible disk models for simulated galaxies. Chapter 7 presents conclusions and discusses future work that can lead on from this thesis. i Acknowledgements I would like to acknowledge the support of my supervisor, Mark Wilkinson, and the Theoretical Astrophysics Group at the University of Leicester. I acknowledge the STFC for financial support throughout my PhD. This research used the Complexity HPC cluster at Leicester which is part of the DiRAC2 national facility, jointly funded by STFC and the Large Facilities Capital Fund of BIS. Chapter 2 Acknowledgements: This work made use of THINGS, “The HI Nearby Galaxy Survey” (Walter et al., 2008). This work is based [in part] on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. We would like to thank Walter Dehnen, Justin Read, Lia Athanassoula, Rodrigo Ibata for valuable discussions. We wish to thank the anonymous referee for their useful comments. The CosmoMC code was written by Anthony Lewis (Lewis and Bridle, 2002). We would also like to thank Erwin de Blok for providing model data (de Blok et al., 2008) in electronic format. MIW acknowledges the Royal Society for support through a University Research Fellowship. PRH acknowledges STFC for financial support. This research used the ALICE High Performance Computing Facility at the University of Leicester. Some resources on ALICE form part of the DiRAC Facility jointly funded by STFC and the Large Facilities Capital Fund of BIS. The project also made extensive use of the Complexity HPC cluster at Leicester which is part of the DiRAC2 national facility. Chapter 3 Acknowledgements: This work made use of THINGS, “The HI Nearby Galaxy Survey” (Walter et al., 2008). This work is based [in part] on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. We would like to thank Walter Dehnen, Albert Bosma and Martin Bourne for valuable discussions. The CosmoMC code was written by Anthony Lewis (Lewis and Bridle, 2002). We would also like to thank Erwin de Blok for providing model data (de Blok et al., 2008) in electronic format. MIW acknowledges the Royal Society for support through a University Research Fellowship. PRH acknowledges STFC for financial support. This research used the Complexity HPC cluster at Leicester which is part of the DiRAC2 national facility, jointly funded by STFC and the Large Facilities Capital Fund of BIS. Chapter 4 Acknowledgements: This work is based [in part] on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. The CosmoMC code was written by Anthony Lewis (Lewis and Bridle, 2002). We thank Edvige Corbelli for supplying the initial rotation curve decompositions. We acknowledge Wyn Evans for valuable discussions during a visit by MIW to the Aspen Center for Theoretical Physics, and Simon White for bringing work on M33 to our attention. We are grateful to the anonymous referee for detailed comments which improved the final version of the paper, and ii to Carlos Frenk for useful comments. MIW acknowledges the Royal Society for support through a University Research Fellowship. PRH acknowledges STFC for financial support. This research used the Complexity HPC cluster at Leicester which is part of the DiRAC2 national facility, jointly funded by STFC and the Large Facilities Capital Fund of BIS.