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Exploring dark matter locally via a hierarchy of stellar systems

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Quinn, Damien Patrick 


Most of our knowledge of the cosmos comes from the light from astronomical sources. However, in the last 40 years a concensus has emerged in the astronomical community that most of the matter in the -universe is invisible i.e it does not absorb or emit electromagnetic radiation. The nature of this dark matter remains an unsolved mystery. In this thesis we attempt to discover what constraints can be placed on dark matter from an analysis of a variety of stellar systems in the Local Group. The simplest composite stellar system is a stellar binary. The separation distribution function of wide binaries is sensitive to the presence of massive compact bodies such as MACHOs. Extending earlier work we use radial velocities measurements to validate a number of objects in the existing sample of wide halo binary candidates, and with the updated sample we study the constraints on MACHOs, arriving at the conclusion that the current wide binaries sample places only very weak constraints on MACHOs, in constrast to earlier work which concluded that the separation distribution of wide halo binaries may be used to rule out MACHOs as a significant component of the dark sector. Motivated by the need to increase the sample size of wide binaries in order to derive more robust constraints, we conducted a search in the Stripe 82 catalog for new systems. A small number of new wide binary systems were detected. These by themselves do not have significant implications for MACHOs, but we outline with illustrations their potential scientific importance, including for testing ideas about wide binary formation. Stepping up the stellar hierarchy we investigate the effect of a lumpy potential on the profile of the tidal tails of a disrupting globular cluster and compare our results to the Pal 5 tidal tail system. We find that a close encounter with a massive dark matter subhalo could produce features in the tails that resemble the current observations. We also show that the Pal 5 system can be used to place new, although not very tight, constraints on MACHOs. The final stellar system we consider is the galactic-wide Planetary Nebula system in the Andromeda galaxy. Along with the galaxy's rotation curve, we use the Planetary Nebulae to constrain dynamical models of the galaxy, with a view to pinning down the parameters of the dark matter halo. We find that the current data is not able to lift the disk/dark matter degeneracy, and show that better gas rotation curve data rather than Planetary Nebulae data may provide the best way forward to achieve this goal.


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Doctor of Philosophy (PhD)

Awarding Institution

University of Cambridge