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Elemental Abundances in the Local Group: Tracing the Formation History of the Great Andromeda Galaxy

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Elemental Abundances in the Local Group: Tracing the Formation History of the Great Andromeda Galaxy Elemental Abundances in the Local Group: Tracing the Formation History of the Great Andromeda Galaxy Thesis by Ivanna A. Escala In Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy CALIFORNIA INSTITUTE OF TECHNOLOGY Pasadena, California 2020 Defended 2020 May 29 ii © 2020 Ivanna A. Escala ORCID: 0000-0002-9933-9551 All rights reserved iii Para mi familia, y para mi iv ACKNOWLEDGEMENTS I would like to thank the many people that have provided me with guidance through- out my thesis, and who have helped me reach the point in my life defined by this achievement. It would have been infinitely more challenging without you all, and I am grateful beyond words. First and foremost, I would like to thank my thesis advisor, Evan N. Kirby, for always making his students a priority. He has been an invaluable mentor, teacher, collaborator, and friend. I am especially thankful that Evan had enough trust in my ability as a competent and independent scientist to be supportive of my extended visit to Princeton. I am privileged to have him as an advisor. I would also like to thank my various mentors throughout my undergraduate edu- cation at the University of California, San Diego, to whom I am indebted: Adam J. Burgasser, who granted me my first opportunity to do research in astronomy, and who believed in me when I most needed it; Dušan Kereš, who helped me develop my skills as a nascent researcher with immeasurable patience and kindness; and Alison Coil, who provided me with much appreciated advice and support on the challenges of navigating a career in astronomy. I would additionally like to thank my beautiful home state of California for providing me with an attainable path to higher education, in part by covering the cost of my undergraduate tuition. Furthermore, I would like to express my gratitude to the additional mentors I had throughout my graduate career: Karoline M. Gilbert, who generously shared her expertise on M31 with me, and who invested significantly in my mentorship despite being a coast apart; Andrew Wetzel, who helped me find my footing as a first year graduate student, and under whose mentorship that I published my first paper; Jenny Greene, who magnanimously hosted me at Princeton during my extended visit; and Robyn E. Sanderson, who worked together with me to create Caltech Women in Physics, Mathematics, and Astronomy, and who provided me with valuable advice. Thank you all for advocating on my behalf. I would like to thank our small Elemental Abundances in M31 collaboration (Evan N. Kirby, Karoline M. Gilbert, and Jennifer Wojno) for providing a wonderful and friendly environment that enabled me to flourish as a researcher. I would like to express my thanks to Princeton Astrophysics, for working to accommodate my bicoastal marriage, and for welcoming me into their department as a visitor. v Thanks to my thesis committee, Chuck Steidel, Philip F. Hopkins, Jim Fuller, Raja GuhaThakurta, Karoline M. Gilbert (informally), and formerly Shri Kulkarni, for providing me with feedback on my thesis plans, and for convening virtually for my defense, despite the fact that I will not be able to provide them with donuts. Of course, my time in graduate school would not have been the same without the fantastic community of astronomy graduate students at Caltech. My decision to accept Caltech’s offer of admission was partially motivated by this tight-knight community, and to this day I am certain that I made the best decision for myself by choosing Caltech astronomy. In particular, I would like to thank my cohort, Anna Y.-Q. Ho, Kaew Tinyanont, Yuguang Chen, and formerly Bhawna Motwani, for all the years we spent together advancing through the program. I am honored to be graduating with some of you this spring, and I look forward to seeing our careers progress. I would also like to extend special thanks to Nicha Leethochawalit and Gina Duggan, my seniors in the Kirby group, Jacob Jencson, for being a joy to have in the department, Denise Schmitz, for being a friend within the Hopkins group, and Tim Miller, who helped to make my first year of graduate school hilarious, despite his short time as a visitor at Caltech. These acknowledgments would not be complete without mentioning Matthew E. Orr, my best friend throughout graduate school. I am thankful to have great memories of our many runs through La Cañada, the Hahamongna Watershed Park, and the Angeles National Forest, our expensive lattes from Copa Vida, our equally expen- sive cocktails from various bars across Los Angeles, and of course, the infamous “Goodbye Forever Tim.” I am indebted to Matt for many reasons, most of all that he helped show me how to not be a robot (although I am glad that I retained some of my robotic tendencies) and the meaning of the phrase “Treat yo self.” It is undeniable that I could not have gotten by without a little help from my friends. Moving across coasts, albeit temporarily, in the middle of graduate school was no small burden, and I could not have shouldered it without a few irreplaceable friends. I owe much to Matt Orr, Nina Tompkin and Dimitar Ho, and Anna Ho, for assisting me with the physical act of moving, for generously hosting me throughout my various visits to Caltech while I was living in Princeton, and especially for letting me couch-surf for weeks upon my return to Caltech, when I was looking for housing in Pasadena’s impossible market. Nina and Dim are among my most favorite people in the world, and I am so grateful that they have always stood by my side. Anna is a scientific force of nature to behold, and she is one of the most moral and trustworthy vi people that I will ever know. I sincerely hope that I will have the opportunity to return the innumerable favors of my friends, and to go beyond merely returning them in the future. I would like to extend my heartfelt thanks to Anita, Ramin, and Shayda Abidi, my second family. The Abidis opened their home in San Diego to me and provided me with an endlessly warm and welcoming environment to further my undergraduate education. In all her kindness, Anita looked after me as if I was her own daughter; Ramin served as a role model to me, and taught me how to be “happily dissatisfied” in order to move forward in life; and Shayda was always full of encouragement for me and my scientific pursuits, and will always be one of my best friends. Above all, I have undertaken this thesis for myself. But I have also done it for my family, to take full advantage of the educational opportunities that they did not have, but for which they sacrificed. For my mother, Ivannia C. Rodriguez Escala, who left everything she knew in her home country of Costa Rica to move to the United States so that I could be born an American citizen. For my father, Richard E. Escala, who worked so hard to provide for his family that, to this day, he has never taken the time off to return to his home country of Argentina. My mother is a shining beacon of fathomless understanding, compassion, and joy in the face of even the darkest parts of the world. My father is the epitome of self-reliance, unbreakable will, and admirable work ethic, even in the face of crippling global crises. I owe who I am to them, and I hope to embody the best of the both of them. I would also like to thank my in-laws, Randal Moseley and Michele Dearmijo Moseley, for their unwavering support of my scientific career, and for offering to assist with the logistical challenges of a bicoastal marriage. Randy and Michele have become a reliable foundation in my life, and it is very meaningful to me that they have continually asked after my doctoral degree progress. Last, but farthest from least, I would like to thank the love of my life, my husband, Eric R. Moseley. Eric is undoubtedly my biggest fan—he is a bottomless well of support, affection, praise, and devotion. He has thought the world of me, and it has made all the difference. His willingness to move from Princeton to California to be together for the remainder of the global pandemic is the single greatest thing that anyone has done for me in my short life. I am eternally grateful that my time as a graduate student at Caltech brought us together1, and I look forward to helping to shape the future of astronomy and astrophysics together. 1This is your fault, Evan. vii ABSTRACT The Local Group (LG) is an environment accessible to detailed studies of galaxy formation, providing a complement to the early universe. In particular, spectroscopy of resolved stellar populations in the LG provides kinematical and chemical infor- mation for individual stars that can be used to infer the history of !¢ galaxies like the Milky Way (MW) and Andromeda (M31). The Gaia revolution in the MW, combined with spectroscopy from APOGEE and other surveys, has enabled comprehensive observational studies of the MW’s forma- tion history. In addition, comparisons to simulations can be leveraged to maximally utilize such observational data to probe the hierarchical assembly of galaxies. To- ward this goal, I have analyzed simulations of chemical evolution in LG dwarf galaxies to assess their ability to match observations. The exquisite detail in which the MW has been studied is currently not achievable in any other !¢ galaxy.
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