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Astro-Archaeology in the Triangulum Galaxy ASTRO-ARCHAEOLOGY in the TRIANGULUM GALAXY

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Astro-Archaeology in the Triangulum Galaxy ASTRO-ARCHAEOLOGY in the TRIANGULUM GALAXY Astro-Archaeology in the Triangulum Galaxy ASTRO-ARCHAEOLOGY IN THE TRIANGULUM GALAXY: STUDYING GALAXY FORMATION AND EVOLUTION WITH THE GLOBULAR CLUSTERS AND STELLAR HALO IN M33 By ROBERT COCKCROFT , M.Sci., M.Sc. A Thesis Submitted to the School of Graduate Studies in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy McMaster University c Robert Cockcroft, September 2012 DOCTOR OF PHILOSOPHY (2012) McMaster University (Physics and Astronomy) Hamilton, Ontario TITLE: Astro-Archaeology in the Triangulum Galaxy: Studying Galaxy For- mation and Evolution with the Globular Clusters and Stellar Halo in M33 AUTHOR: Robert Cockcroft, M.Sci. (University College London), M.Sc. (Mc- Master University) SUPERVISOR: Professor William E. Harris NUMBER OF PAGES: xxi, 231 ii Abstract The currently-favoured cosmological paradigm, ΛCDM, predicts that galaxies are built up from smaller galaxies in a bottom-up process known as hierar- chical merging. ΛCDM is extremely successful for large-scale structures, but is less so for the detailed features of individual galaxies. We can study these features - the galaxies’ foundations and the remnants of the smaller compo- nents that built them - only in the closest galaxies in which we can resolve individual stars. In this thesis, we use data from the Canada-France-Hawaii Telescope (CFHT)/MegaCam as part of the Pan-Andromeda Archaeological Survey (PAndAS) to observe M33 (the Triangulum Galaxy) and the detailed features of its old stellar population. The study of these details is vital for our understanding of galaxy formation and evolution. We search for two types of components within the old stellar population: globular star clusters and the faint, diffuse stellar halo. We find only one new unambiguous outer halo star cluster, in addition to the five previously known in the M33 outer halo (10 kpc . r . 50 kpc). A further 2440 cluster candidates are identified, which we analyse using two different types of simulated clusters. We are able to describe the type of clusters that are likely to remain hidden from our searches. Our study of a population of red giant branch (RGB) stars far from the M33 disk reveals a low-luminosity, centrally concentrated component which we interpret as the discovery of M33’s halo. It is everywhere in our data fainter than µ 33 mag arcsec−2, with scale length r 20 kpc, an overall V ∼ exp ∼ luminosity not more than a few percent of the total luminosity of M33, and is possibly also not azimuthally symmetric. For M33 to have so few outer halo clusters compared to M31 and to have such a low-luminosity halo, with the possible asymmetry that we see, suggests tidal stripping of M33’s halo components by M31 - a view that is also favoured by the morphology of the disk substructure and recent modelling. iii To Mum and Dad Co-Authorship Chapters 2 and 4 are original papers written by myself, Robert Cockcroft, and have been re-formatted to conform to the specifications of the McMaster thesis style. Chapter 2 was published in The Astrophysical Journal, with reference Cockcroft, R.; Harris, W. E.; Ferguson, A. M. N.; Huxor, A.; Ibata, R.; Irwin, M. J.; McConnachie, A. W.; Woodley, K. A.; Chapman, S. C.; Lewis G. F.; and, Puzia, T. H., Volume 730, Issue 2, pages 112-123, Bib. Code: 2011ApJ...730..112C, DOI: 10.1088/0004-637X/730/2/112. Chapter 4 was submitted to The Monthly Notices of the Royal Astronomical Society on 22nd May 2012, and now contains the revised manuscript, submitted in response to the referee’s comments on 28th August 2012. The listed authors are Cockcroft, R.; McConnachie, A. W.; Harris, W. E.; Ibata, R.; Irwin, M. J.; Ferguson, A. M. N.; Fardal, M. A.; Babul, A.; Chapman, S. C.; Lewis, G. F.; Martin, N. F.; and, Puzia, T. H. Authorship guidelines for papers that use data from the Pan-Andromeda Archaeological Survey (PAndAS), as the above papers do, suggest that after the main researchers (in this case, R. Cockcroft, W. E. Harris and A. Mc- Connachie), R. Ibata and M. J. Irwin are listed for their contribution to the program proposal and subsequent data reduction, in addition to other group members who have made contributions the paper (which can include sugges- tions to improve paper drafts, but does not guarantee co-authorship). Chapters 1 (the introduction), 3 and 5 (the summary) are also my original work, with the exception of the Chapter 1’s figures. I have obtained permission to use these figures in my thesis from the authors. Chapter 3 is a paper in preparation, and will have co-authors Harris, W. E.; Ibata, R.; Irwin, M. J.; Barmby, P.; Leigh, N.; Umbreit, S.; Sills, A.; Glebbeek, E.; Woodley, K. A.; and, Fabbro, S. I grant an irrevocable, non-exclusive license to McMaster University and to Library and Archives Canada to reproduce this material as part of this thesis. vi Acknowledgements Throughout my studies in astronomy, I have received much mentorship, guid- ance and support - most especially from my supervisor, Dr Bill Harris, to whom I am sincerely grateful. I have had the privilege to work with Bill over the past six years, and admire the way he not only navigates deftly through the research projects in an efficient yet relaxed manner, but can also instill confidence and composure in me. I am also deeply indebted to Drs Pauline Barmby, Laura Parker and Alison Sills, my supervisory committee members, who have greatly contributed throughout the years with fresh perspectives, ideas and encouragement. My research has allowed me to meet many other motivational people, and I would like to thank Drs Alan McConnachie, Annette Ferguson, Avon Huxor, Mike Irwin, Nathan Leigh, Kristin Woodley and everyone on the PAn- dAS and CFHT teams. The outreach projects that I have undertaken at McMaster University constantly remind me of the reasons why I enjoy studying astronomy. It has been my pleasure to share my passion for outreach with my friends, colleagues and role models, Drs Sarah Symons, Doug Welch, Ralph Pudritz, and Mike Reid, and Caroline Burgess - inspirations, all of them. Important for any department to work effectively is a strong team of support staff, and we are very fortunate to have one here in the Department of Physics and Astronomy. Mara Esposto, Cheryl Johnston, Rosemary McNiece, Liz Penney and Tina Stewart: thank you so much for enabling my various jobs to run so smoothly and also making them much more enjoyable and fun in the process. Finally, many heart-felt thanks to my family and friends: to my parents, my brother and sister and their families, my grandparents, my partner and his family, and all of my friends at University College London and McMaster University who have joined me at various stages along my path in astronomy. vii Mum and Dad, thank you especially to you, for always being there, and for walking that fine line between giving me your honest opinions while constantly supporting whatever decision I make. Cal, you grew up being my little sister, but I think of you in many ways as a big sister now for the strength and sensibility you show. I look forward to seeing you and Pippa more in the near future. Andrew, it’s always a pleasure to see you and your beautiful family. I’d be happy to be half as successful as you are by the time I’m your age. And to Ken: I know you hate roller coasters, but thank you more than you know for joining me on this one. I could not have done it without you. Our future together is going to be exciting, and I’m very much looking forward to it! viii “God does not play dice with the universe; [S]He plays an ineffable game of [her/]his own devising, which might be compared, from the perspective of any of the other players, to being involved in an obscure and complex version of poker in a pitch dark room, with blank cards, for infinite stakes, with a dealer who won’t tell you the rules, and who smiles all the time.” Neil Gaiman (b. 1960), and Terry Pratchett (b. 1948) “Why should we demand that the universe make itself clear to us? Why should we care?... It is something about understanding the totality of existence, the essential defining reality of things, the entire universe and [our] place in it. It is a groping among stars for final answers, a wandering the infinitesimal for the infinitely general, a deeper and deeper pilgrimage into the unknown.” Julian Jaynes (1920-1997) “The final mystery is oneself. When one has weighed the sun in the balances, and measured the steps of the moon, and mapped out the seven heavens star by star, there still remains oneself. Who can calculate the orbit of [her/]his own soul?” Oscar Wilde (1854-1900) “There are many windows through which we can look out into the world, searching for meaning... Most of us, when we ponder on the meaning of our existence, peer through but one of these windows onto the world. And even that one is often misted over by the breath of our finite humanity. We clear a tiny peephole and stare through. No wonder we are confused by the tiny fraction of a whole that we see. It is, after all, trying to comprehend the panorama of the desert or the sea through a rolled-up newspaper.” Jane Goodall (b. 1934) x Table of Contents Abstract iii Co-Authorship vi Acknowledgments vii List of Figures xv List of Tables xviii List of Acronyms xix Chapter 1 Introduction 1 1.1 TheLambdaColdDarkMatterParadigm .
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