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Globular Clusters in the Local Group As Probes of Galaxy Assembly

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Globular Clusters in the Local Group As Probes of Galaxy Assembly This thesis has been submitted in fulfilment of the requirements for a postgraduate degree (e.g. PhD, MPhil, DClinPsychol) at the University of Edinburgh. Please note the following terms and conditions of use: • This work is protected by copyright and other intellectual property rights, which are retained by the thesis author, unless otherwise stated. • A copy can be downloaded for personal non-commercial research or study, without prior permission or charge. • This thesis cannot be reproduced or quoted extensively from without first obtaining permission in writing from the author. • The content must not be changed in any way or sold commercially in any format or medium without the formal permission of the author. • When referring to this work, full bibliographic details including the author, title, awarding institution and date of the thesis must be given. Globular clusters in the Local Group as probes of galaxy assembly Jovan Veljanoski Doctor of Philosophy The University of Edinburgh 13 June 2014 Lay Summary Understanding the formation and evolution of galaxies is one of the most active areas of research in astrophysics. Gradual build-up of matter by merging pre-galactic fragments is the current preferred model of constructing massive galaxies. A key prediction of this theory is that outskirts nearby galaxies should contain remnants of this assembly process in the form of fragmented stellar streams. Found in all but the smallest of galaxies, globular star clusters (GC) are excellent probes for studying properties of galaxies. Having high luminosities, they are favourable targets in the outer regions of galaxies where the associated stellar surface brightness is low. GCs are thought to be amongst the oldest stellar systems in the Universe, and are likely born in the most significant phases of galaxy formation. Their metal abundances, ages, spatial positions and motions can be used to constrain the assembly history of their host galaxy. In this thesis, I explore in great detail the motions and the light coming from GC systems in several nearby galaxies. The work is based on a major spec- troscopic campaign, follow-up to the Pan-Andromeda Archaeological Survey (PAndAS), a large imaging program, designed to observe the Andromeda galaxy. Line-of-sight velocities are obtained for 78 GCs in the far outskirts of Andromeda, 63 of which were not studied before. In addition, GCs in the dwarf galaxies NGC 147, NGC 185 and NGC 6822 are also spectroscopically observed. By conducting a detailed analysis, I find that GCs in the remote regions of Andromeda exhibit significant degree of rotation, which is in the same direction as for the GC located in the heart of the galaxy. My analysis of the GC motions located in the outskirts of Andromeda give further clues about how this galaxy got assembled through merging of smaller dwarf galaxies. I also estimate the total mass of Andromeda using the motions of its remote GC system. i I also characterize the GC systems of three dwarf galaxies in the Local Group: the dwarf elliptical satellites of M31, NGC 147 and NGC 185, and the isolated dwarf irregular NGC 6822. Using uniform optical and near-IR imagery, I constrain the age and metal abundance of their constituent GCs. The GCs around NGC 147 and NGC 185 are found to lack metals, as is typically the case for these type of objects, while their ages are more difficult to constrain. On the other hand, the GCs hosted by NGC 6822 are found to be very old, but with a variety of metal abundances. Finally, I analyse the motions of the GCs in these three systems, and use them to constrain the masses of the respective host galaxies. ii Abstract Understanding the formation and evolution of galaxies is one of the most active areas of research in astrophysics. Hierarchical merging of proto-galactic fragments to build more massive galaxies is the current preferred model. A key prediction of this theory is that haloes of nearby galaxies should contain remnants of this assembly process in the form of tidal debris. Found in all but the smallest of dwarf galaxies, globular clusters (GC) are ex- cellent probes of galaxy haloes. Having high luminosities, they are favourable targets in the outer regions of galaxies where the associated stellar surface brightness is low. GCs are thought to be amongst the oldest stellar systems in the Universe, and are likely born in the most significant phases of galaxy formation. Their metallicities, ages, spatial distributions and kinematics can be used to constrain the assembly history of their host galaxy. In this thesis, I explore the photometric and kinematic properties of several GC systems in our cosmological backyard, the Local Group of galaxies. The work is based on a major spectroscopic campaign, follow-up to the photometric Pan- Andromeda Archaeological Survey (PAndAS), as well as additional optical and near-IR data sets. Radial velocities are obtained for 78 GCs in the halo of M31, 63 of which had no previous spectroscopic information. The GCs have projected radii between 20 and 140 kpc, thus sampling the true outer halo ∼ of this galaxy. In addition, GCs in the dwarf galaxies NGC 147, NGC 185 and NGC 6822 are also spectroscopically observed. By conducting a detailed kinematic analysis, I find that GCs in the outer halo of M31 exhibit coherent rotation around the minor optical axis, in the same direction as their more centrally located counterparts, but with a smaller amplitude of 86 17 km s 1. There is also evidence that the velocity ± − dispersion of the outer halo GC system decreases as a function of projected radius from the M31 centre, and this relation can be well described by a power law of index 0.5. I detect and discuss various velocity correlations amongst ≈− GCs that lie on stellar streams in the M31 halo. Simple Monte Carlo tests iii show that such configurations are unlikely to form by chance, implying that significant fraction of the GCs in the M31 halo have been accreted alongside their parent dwarf galaxies. I also estimate the dynamical mass of M31 within 200 kpc to be (1.2 1.6) 0.2 1012 M . − ± × ⊙ I also characterize the GC systems of three dwarf galaxies in the Local Group: the dwarf elliptical satellites of M31, NGC 147 and NGC 185, and the isolated dwarf irregular NGC 6822. Using uniform optical and near-IR photometry, I constrain the ages and metallicities of their constituent GCs. The metallicities of the GCs around NGC 147 and NGC 185 are found to be metal-poor ([Fe/H]. 1.25 dex), while their ages are more difficult to constrain. The − GCs hosted by NGC 6822 are found to be old (>9 Gyr) and to have a spread of metallicities ( 1.6 . [Fe/H] . 0.4). I find close similarity between the − − mean optical (V I) colours of the GCs hosted by these three dwarf galaxies − 0 to those located in the M31 outer halo, consistent with the idea that dwarf galaxies akin to them might have contributed toward the assembly of the M31 outer halo GC population. Analysing their kinematics, I find no evidence for systemic rotation in either of these three GC systems. Finally, I use the available GC kinematic data to calculate the dynamical masses of NGC 147, NGC 185 and NGC 6822. iv Declaration I declare that this thesis was composed by myself, that the work contained herein is my own except where explicitly stated otherwise in the text, and that this work has not been submitted for any other degree or professional qualification except as specified. Parts of this work have been published in Veljanoski, J. et al., 2013, ApJL, 768, 33L Veljanoski, J. et al., 2013, MNRAS, 435, 3654 Veljanoski, J. et al., 2014, MNRAS, in press. (Jovan Veljanoski, 13 June 2014) v Acknowledgements First of all, I would like to thank my supervisor, Annette Ferguson both for the fantastic opportunity you have given me, and for your guidance throughout this journey. You have shown me what it means to be a top-notch and yet a humble researcher, have given me the best example of academic excellence and professionalism, and I can not describe how much I have learned from you. I would like to thank my friends and colleagues Edouard Bernard and Denija Crnojevi´c for the countless talks, support and encouragement, inside and outside the office. You were there every time for me, for work and for fun. A big thanks to Dougal Mackey; although I am yet to meet you in person, working together with you was a great experience and I am thankful for all of your e-mails with detailed explanations and comments. Many thanks to Mike Irwin, Avon Huxor, Pat Côté and the rest of the PAndAS collaboration for making this project possible. I would like to thank Jorge Peñarrubia for teaching me the art of statistics, and Alexander Rogers for teaching me how to python with style. In addition, I would like to thank Jim Dunlop, Ross McLure, Ken Rice, Philip Best, John Peacock and all the rest former and present IfA staff members for their help and support throughout my studies in Edinburgh. I am also grateful to the postdocs and fellow Ph.D. students with whom I had many interesting discussions. Thanks to José Sabater Montes, Sylvain de la Torre, Fernando Buitrago, Massimo Viola, Isaac Roseboom, Eric Tittly, Ami Choi, Emma Curtis-Lake, Esther Marmol-Queralto, Michal Michalowski, Mike Barker, Victoria Bruce, Duncan Forgan, Tom Target, Pratika Dayal, Maciej Koprowski, Joao Ferreira, Rebecca Bowler, Vinod Arumugam, Marika Asgari, Chris Duncan, Alexandar Mead, Jack Mayo, Henry Pearce and all the rest of the team.
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