The Neutral Hydrogen Content of Satellite Galaxies in the Local Volume by Ananthan Karunakaran A thesis submitted to the Department of Physics, Engineering Physics & Astronomy in conformity with the requirements for the degree of Master of Science Queen’s University Kingston, Ontario, Canada November, 2017 Copyright © Ananthan Karunakaran, 2017 Abstract The properties of the satellite populations of galaxies are vital for understanding their structure and evolution in a cosmological context. Deep optical imaging surveys have revealed a host of low surface brightness (LSB) features near Local Volume galaxies, that may be satellites of the latter. We conduct atomic gas (HI) observations of 48 such satellite candidate galaxies discovered around 10 different hosts using the Robert C. Byrd Green Bank Telescope. Detections of HI reservoirs in these systems will provide spectroscopic distances that can be used to confirm an association to their putative hosts. Non-detections imply that the objects are gas-poor, irrespective of their distance along the line-of-sight. We first search for HI in six ultra-faint dwarf candidates discovered near NGC 3109. One is detected in HI, placing it in the background as a gas-rich field dwarf, while the remaining five have no detectable HI emission. We also searched for HI along the lines of sight to 27 LSB features that project around M101, and the majority (23/27) were found to be gas-poor. The other four were detected in HI, though only one has a recessional velocity consistent with that of M101. Two of the other galaxies have systemic velocities suggesting an association with a background group and the fourth detection places it in the background. Finally, we searched for HI in 15 satellite candidates around 8 hosts i ii finding just one gas-rich satellite. Using the HI and optical properties of all non- detections, we compare them with other samples of dwarf galaxies. We find that in order for our non-detections to be consistent with well-studied scaling relations for gas-rich field galaxies, the most plausible scenario is that the Local Volume LSBs are associated with their hosts, the M101 candidates are associated with it or the background group, and the satellite candidates around NGC 3109 are in fact field galaxies that have distances in the range 17.5-38 Mpc. Therefore, both detections and non-detections place important constraints on the physical properties of candidate satellite galaxies detected in the optical. Acknowledgments It goes without saying that I would not have had the wonderful opportunity to conduct such interesting research and pursue my passion without the guidance and support from my supervisor, Kristine Spekkens. Thank you. To my friends in the department at Queen’s University, I have no idea where these last two years have gone but I am extremely thankful that I was able to spend it with such amazing people. I would like to thank Matthew Chequers, Zsolt Keszthelyi, Colin Lewis, James Sikora, and Cory Wagner for all of your advice and countless discussions, whether personal or research related. To my friends from FMM and Mac, I will always appreciate your support and for keeping me grounded. This is one step closer to the dream! I don’t know where I would be without the love, encouragement, and support from my family. I would like to specifically thank my sister, Amirtha, for always being there for me and keeping me focused on what is important. “Sometimes science is more art than science, Morty. A lot of people don’t get that.” iii Statement of Co-Authorship All of the work presented in thesis was completed by the author, including the HI observations, data reduction, and analysis. In Chapter3, the optical imaging campaigns around NGC 3109 and the result- ing photometric analysis (from which our HI follow-up target list was drawn) were conducted by collaborator D. Sand at the University of Arizona. The pre-publication optical properties of target galaxies, reduced images (e.g. Figure 3.1), and raw images used in this thesis were provided by him through private communication. In Chapter4, previous and ongoing HST imaging campaigns and preliminary analysis of the targeted M101 satellite candidates were conducted by collaborator P. Bennet at Texas Tech University. Distance information for M101-Dw6 gleaned from a preliminary analysis of those data was provided by him through private communi- cation. iv Contents Abstracti Acknowledgments iii Statement of Co-Authorship iv Table of Contentsv List of Tables viii List of Figures ix List of Acronyms xii List of Symbols xiv Chapter 1 Introduction1 1.1 Cosmological Structure Formation ................... 6 1.2 Comparing Satellites in Simulations and Observations ........ 9 1.3 The Low Surface Brightness Universe.................. 13 1.3.1 The Local Group......................... 13 1.3.2 Dwarfs in Nearby Systems.................... 15 v CONTENTS vi 1.3.3 Low Surface Brightness Galaxies ................ 18 1.4 HI in Low-Mass Galaxies ........................ 22 1.4.1 Neutral Hydrogen......................... 22 1.4.2 HI in the Local Group...................... 24 1.4.3 Gas-Rich Field Galaxies ..................... 27 1.5 This Work................................. 31 Chapter 2 Observations and Data Reduction 33 2.1 Observations................................ 33 2.1.1 Single-Dish Radio Telescopes .................. 33 2.1.2 The Green Bank Observatory.................. 36 2.1.3 Instrument Setup......................... 39 2.1.4 Observations with the GBT................... 40 2.2 Data Reduction.............................. 44 2.3 Conclusions................................ 52 Chapter 3 Satellite candidates around NGC 3109 54 3.1 The NGC 3109 System and New Satellite Candidates......... 54 3.2 HI Observations and Analysis...................... 59 3.2.1 Observations ........................... 59 3.2.2 Analysis.............................. 60 3.3 Discussion................................. 67 3.4 Conclusions................................ 74 Chapter 4 The Satellite Population around M101 76 4.1 The M101 Group............................. 76 CONTENTS vii 4.2 Observations and Analysis........................ 82 4.3 Discussion................................. 94 4.3.1 Satellites of M101......................... 94 4.3.2 Galaxies in the Background ................... 101 4.4 Conclusions................................ 103 Chapter 5 The Satellite Populations of Local Volume Galaxies 105 5.1 Galaxies in the Local Volume ...................... 105 5.2 Observations and Analysis........................ 108 5.3 Discussion and Conclusions ....................... 114 Chapter 6 Discussion 119 6.1 Our Non-Detections as Satellites..................... 120 6.2 Our Non-detections as Background Galaxies.............. 124 6.3 Constraining Distances to Non-Detections . 131 Chapter 7 Conclusions and Future Work 133 7.1 Future Work................................ 136 Bibliography 139 List of Tables 3.1 Properties of existing satellites and new satellite candidates around NGC 3109................................. 58 3.2 Details of HI observations of the LSB features............. 60 3.3 Upper limits for range of distances of LSB features projected around NGC 3109................................. 66 3.4 Properties of Dw1 ............................ 66 3.5 Details of potential host galaxies for Dw1. ............... 68 4.1 M101 satellite candidates and their observations ........... 84 4.2 Upper limits for confirmed satellites, satellite candidates, and back- ground galaxies that are projected around M101............ 92 4.3 Properties of candidate satellites with HI detections ......... 93 5.1 Properties of Local Volume Hosts in our sample............ 107 5.2 Local Volume satellite candidates and their observations . 109 5.3 Upper limits for satellite candidates with HI non-detections calculated at the distance of their putative host .................. 112 5.4 Properties of the satellite with HI emission . 113 viii List of Figures 1.1 Examples of satellite dwarf galaxies .................. 5 1.2 Milky Way-size dark matter halos from Aquarius simulations .... 8 1.3 Cumulative mass function from ELVIS simulations for Milky Way-like halos.................................... 11 1.4 Luminosity-Size plane for faint satellites and star clusters of the Milky Way .................................... 16 1.5 LSBs around M101 discovered by Merritt et al.(2014) . 20 1.6 Ratios of HI mass to V-band luminosity and HI mass to dynamical mass for Milky Way dwarf spheroidals ................. 27 1.7 Gas mass versus stellar mass for isolated and non-isolated systems . 30 2.1 The Green Bank Telescope (GBT) ................... 37 2.2 Azimuthally averaged beam pattern of GBT.............. 38 2.3 Observing script example......................... 42 2.4 Software used during observations with the GBT ........... 43 2.5 Examples of radio frequency interference features in our spectra . 46 2.6 RFI removal process ........................... 49 2.7 RFI removal histogram.......................... 51 2.8 Examples of final spectra for detections and non-detections . 52 ix LIST OF FIGURES x 3.1 DECam image of ultra-faint dwarf galaxy candidates around NGC 3109 57 3.2 Spectra for LSB features around NGC 3109 with HI non-detections . 61 3.3 GBT HI spectrum for NGC 3109-Dw1 showing clear emission at vHelio ∼ 1060 kms−1 ................................ 62 3.4 Example of our analysis method of HI emission detections . 64 3.5 HI-mass and V-band luminosity calculated as a function of distance for LSB features