Characterizing Dwarf and Diffuse Galaxy Populations in the Local Universe by Ananthan Karunakaran A thesis submitted to the Department of Physics, Engineering Physics & Astronomy in conformity with the requirements for the degree of Doctor of Philosophy Queen’s University Kingston, Ontario, Canada August 2021 Copyright © Ananthan Karunakaran, 2021 Abstract Extragalactic astronomy in the last decade has greatly benefited from significant improve- ments to (1) astronomical instrumentation and (2) data reduction and analysis techniques. These improvements afford the ability to reveal ever fainter low surface brightness (LSB) dwarf galaxies at optical wavelengths. Thoroughly characterizing these dwarf galaxies is es- sential in furthering our understanding of how galaxies form and evolve. Accordingly, there have been several concerted efforts to compile and characterize the properties of (1) satellite dwarf galaxies around Milky Way-like systems beyond the Local Group and (2) a subset of large, LSBs known as Ultra-Diffuse Galaxies (UDGs) whose properties fall at the extreme end of the dwarf galaxy population. In this thesis, I will present studies that aim to illumi- nate both of these sub-fields by exploiting their neutral hydrogen (HI) gas and star-forming properties. The first of these studies focus on the HI gas content of LSB dwarf galaxy satellite candidates around the nearby spiral, M101, with the aim of obtaining spectroscopic distance estimates to them via their HI content and investigating any potential environmental trends related to their HI content. The second study compares the quenched and star-forming satellite populations from the Satellites Around Galactic Analogs (SAGA) survey to two state-of-the-art zoom-in hydrodynamical simulation suites, APOSTLE and Auriga, in order to understand the relatively low observed quenched satellite fraction. The second half of this thesis presents an extensive HI follow-up survey of optically-detected UDG candidates from the Systematically Measuring Ultra-Diffuse Galaxies (SMUDGes) survey. This follow-up i survey aims to confirm SMUDGes UDG candidates as bonafide UDGs by obtaining spec- troscopic distances estimates and to place constraints on their formation mechanisms using their HI properties. ii Acknowledgements These last 6 years would not have been possible without the amazing and constant support of my supervisor. Kristine, thank you for teaching and mentoring me in both academic and personal matters and for giving me the opportunity to pursue my passion. I have had to pleasure of getting to know many graduate students in the department at Queen’s and I am grateful for the friendships that have blossomed during my time here. It would have been tremendously more difficult and miserable without you all. To my boys, time has flown by and I can always count on you for reminding me where it all started. Thank you. It seems impossible to thank my amazing family in words for their neverending love, support, and understanding while I pursue my dream. I will forever be indebted to the sacrifices you have all made for me. Thank you so much and I love you all. Finally, to my partner, Jacquie. Thank you for being there for me through my highs and lows, for reminding me that it is okay to step back and take a break, and, of course, for your help with picking out colour palettes for my graphs. I am excited for what our future holds and I love you so much. iii Statement of Co-Authorship The original work presented in this thesis was completed by the author under the supervi- sion of Dr. Kristine Spekkens at Queen’s University. Chapters2,3, and4 are versions of accepted/published journal articles that comply with the copyright permissions of the AAS journals. A brief description of the work done by the author for each article is provided at the beginning of each of these chapters and any contributions from collaborators are explicitly stated. These chapters have not been organized chronologically and instead are organized such that there is a more coherent flow between them. iv Contents Abstract i Acknowledgments iii Statement of Co-Authorship iv Table of Contentsv List of Tables ix List of Figuresx List of Acronyms xii List of Symbols xiv Chapter 1 Introduction1 1.1 Dwarf Galaxies................................... 5 1.1.1 A Brief Census of the Local Group Satellites .............. 5 1.1.2 Gas, Star Formation, and the Role of Environment........... 6 1.1.3 Dwarf Galaxies in Simulations ...................... 9 1.2 Low Surface Brightness Galaxies and Modern LSB Surveys .......... 13 1.2.1 Satellite Systems around Massive Galaxies................ 16 1.2.2 Ultra-Diffuse Galaxies and their Formation Mechanisms . 19 v CONTENTS CONTENTS 1.2.3 LSB and UDG Follow-up Observations.................. 22 1.3 This Work...................................... 24 Chapter 2 Neutral Hydrogen Observations of Low Surface Brightness Galax- ies around M101 and NGC 5485 26 2.1 Abstract....................................... 27 2.2 Introduction..................................... 27 2.3 Sample Selection .................................. 29 2.4 Observations and Data Reduction......................... 31 2.5 Results........................................ 35 2.5.1 HI Detections ............................... 35 2.5.2 HI Non-detections............................. 39 2.5.3 Optical and Gas Properties........................ 39 2.6 Discussion...................................... 42 2.6.1 Associations of HI Detections....................... 43 2.6.2 HI non-detections and the NGC 5485 group .............. 46 2.6.3 Satellite Gas Richness........................... 49 2.7 Conclusions..................................... 50 Chapter 3 Satellites Around Milky Way Analogs: Tension in the Num- ber and Fraction of Quiescent Satellites Seen in Observations Versus Simulations 53 3.1 Abstract....................................... 54 3.2 Introduction..................................... 54 3.3 Satellite Samples.................................. 56 3.3.1 Observed sample: SAGA-II........................ 56 3.3.2 Simulated samples: APOSTLE and Auriga ............... 57 3.4 Identifying Star-Forming Satellites ........................ 59 vi CONTENTS CONTENTS 3.4.1 Observed Star-Forming Satellites..................... 60 3.4.2 Simulated Star-Forming Satellites..................... 61 3.4.3 Comparing Star-Forming Satellites.................... 63 3.5 Observed and Simulated Quenched Fractions .................. 64 3.6 Discussion and Conclusions ............................ 66 3.7 Appendix: Testing Resolution and Star-formation Tracers in Simulations . 73 Chapter 4 Systematically Measuring Ultra Diffuse Galaxies in HI: Results from the Pilot Survey 75 4.1 Abstract....................................... 76 4.2 Introduction..................................... 76 4.3 Sample Selection .................................. 80 4.4 Observations and Data Reduction......................... 81 4.5 Results........................................ 85 4.5.1 Properties of HI Detections........................ 85 4.5.2 HI Non-detections ............................. 92 4.6 Discussion...................................... 97 4.6.1 Comparing UDGs with HI Detections and Non-detections . 98 4.6.2 Constraining Formation Mechanisms...................104 4.6.3 Disk Geometry and the BTFR ......................105 4.7 Conclusions.....................................112 Chapter 5 An Update On and the Outlook of the SMUDGes in HI Survey115 5.1 Introduction.....................................115 5.2 Survey Progress...................................116 5.2.1 SMUDGes in the Legacy Surveys.....................116 5.2.2 SMUDGes in HI ..............................117 5.2.2.1 Campaigns 2 and 3 .......................118 vii CONTENTS CONTENTS 5.2.2.2 Campaigns 4 and 5 .......................118 5.3 Preliminary Results ................................122 5.4 Outlook.......................................129 Chapter 6 Summary and Conclusions 133 6.1 Summary ......................................133 6.1.1 Satellite Galaxies around Milky Way-like Systems . 133 6.1.2 Ultra-Diffuse Galaxies...........................136 6.2 Future Work ....................................139 6.2.1 Satellites around Milky Way-like Systems . 139 6.2.2 Ultra-Diffuse Galaxies...........................140 6.2.3 Upcoming Surveys.............................140 6.3 Conclusions.....................................142 Bibliography 144 viii List of Tables 2.1 Target LSB Dwarf Candidate Properties .................... 34 2.2 Properties of LSB Dwarf Candidates with HI detections ............ 38 2.3 HI Upper Limits for Non-detections....................... 42 3.1 UV properties of Observed satellites ....................... 72 4.1 Target UDG Candidate Properties ........................ 83 4.2 Properties of UDG with HI detections ...................... 89 4.3 HI Properties of Dwarfs .............................. 90 4.4 HI Properties of Non-detections.......................... 95 4.5 Inclinations and Rotation Velocities........................111 5.1 Summary of SMUDGes in HI campaigns.....................120 ix List of Figures 1.1 Compilation of galaxy images demonstrating their diversity .......... 4 1.2 HI masses of Local Group dwarf galaxies as a function of galactocentric distance8 1.3 Comparison of modern simulation projects.................... 12 1.4 Sample of LSB cutouts from HSC-SSP...................... 15 1.5 The Robert C. Byrd Green Bank Telescope ................... 24 2.1 HI detection spectra of LSB satellites