Connecting galactic to local scales in the neutral interstellar medium across the Local Group by Eric William Koch A thesis submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy Department of Physics University of Alberta © Eric William Koch, 2020 Abstract Star formation drives secular galaxy evolution by linking stars and gas in galaxies. This link forms part of the \baryonic cycle," where stars form from interstellar gas, and a portion of that gas is returned to the interstellar medium upon the star's death. Understanding the baryonic cycle and its role in galaxy evolution requires piecing together how the neutral interstellar medium con- trols where and when star formation occurs. However, our understanding re- mains limited because the neutral interstellar medium is affected by processes ranging from the kiloparsec scales of galaxies to the sub-parsec scales where individual stellar systems form. To advance our knowledge of the baryonic cycle and galaxy evolution, observations of the neutral interstellar medium must bridge large to small scales. In my thesis, I present new observations of the Local Group galaxies that connect large to small scales in the neutral interstellar medium in exquisite de- tail. The Local Group galaxies provide an external view to trace galaxy-scale processes but are close enough for current telescopes to resolve < 100 pc scales where key components of the baryonic cycle occur. I present the first part of an on-going Local Group survey of atomic hydrogen taken with the Very Large Array. These observations provide high-spatial and -spectral resolution maps of M31 and M33 produced from my new techniques for handling massive inter- ferometric data sets. I use these new observations to demonstrate the complex kinematics of the atomic interstellar medium and the large bias implicit in ii using approximate line shape measurements. My work demonstrates that de- tailed spectral modeling is critically needed to guide our interpretation of the atomic interstellar medium. Applying detailed spectral modeling, I show that 21-cm HI emission is best modeled as a set of optically-thin Gaussians. I further show that previous results reporting opaque HI on 100 pc scales are strongly rejected by the new observations. I then compare tracers of the atomic and molecular interstellar medium and find strong correlations between their kinematics. The molecular interstellar medium is the direct fuel for star formation, and this correlation indicates a continued role for the atomic interstellar medium throughout the star forma- tion process. However, these correlations are apparent when only the atomic gas spectrally associated with the molecular gas is considered. Previous stud- ies that use all of the atomic gas along the line-of-sight are unlikely to find this association. These results further suggest the need for careful spectral mod- eling to study processes that link the atomic and molecular media, including how molecular gas is formed from the atomic gas. Finally, I demonstrate the difficulties in recovering the source of large- scale turbulence in nearby galaxies, which is a key but poorly constrained component in modern star formation theories. I show that features in the spatial power spectrum, previously interpreted as large-scale galaxy properties, are not physical and instead result from the instrument response function. Because of this, the source of turbulent driving remains ambiguous. By combining high-spectral resolution observations of the atomic interstel- lar medium with detailed modeling, my work opens new avenues for exploring the neutral interstellar medium in nearby galaxies. iii Preface This thesis is original work by Eric William Koch, conducted under the super- vision of Erik W. Rosolowsky. Chapter 3 of this thesis is published in Koch, E.W et al. (2018). \Kinemat- ics of the atomic ISM in M33 on 80 pc scales," MNRAS, 479, 2505{2533. E.W. Rosolowsky led the proposal for the VLA observations. A preliminary reduc- tion of these observations, though later discovered to be flawed, was presented in my MSc. thesis (2016). I planned the observations with E.W. Rosolowsky and A.K. Leroy, performed the data reduction, imaging, and analysis. I led writing the manuscript with input from all authors. Chapter 4 of this thesis is a manuscript in preparation and will be sub- mitted to Monthly Notices of the Royal Astronomical Society as Koch, E.W et al. 2020, "A dearth of tophats in M31 & M33: HI spectra strongly prefer multigaussian over opaque model fits.” A.K. Leroy led the proposal for and planned the M31 VLA observations. I performed the data reduction, imaging, and analysis. I led writing the manuscript in collaboration with J. Chastenet, I. Chiang, A.K. Leroy, E.W. Rosolowsky, K.M. Sandstrom, and D. Utomo. Chapter 5 of this thesis is published in Koch, E.W et al. (2019). \Rela- tionship between the line width of the atomic and molecular ISM in M33," MNRAS, 485, 2324{2342. I used the VLA M33 HI observations from Chapter 3 (Koch et al., 2018c) and CO(2-1) observations taken by the IRAM 30-m telescope that are published in Gratier et al. (2010) and Druard et al. (2014). iv I performed the analysis and led writing the manuscript with input from all authors. Chapter 6 of this thesis is published in Koch, E.W et al. (2020). \Spatial power spectra of dust across the Local Group: No constraint on disc scale height," MNRAS, 492, 2663{2682. Using dust modeling from Utomo et al. (2019a), I performed the analysis and led writing the manuscript with input from all authors. This thesis makes use of observations taken with the NSF's Karl G. Jan- sky Very Large Array and the Green Bank Telescope. The National Radio Astronomy Observatory and the Green Bank Observatory are facilities of the National Science Foundation operated under cooperative agreement by Asso- ciated Universities, Inc. This research was enabled in part by support provided by WestGrid, Com- pute Canada, and CANFAR. v For my ever-supportive family. And Sarah, my partner in all things. vi Acknowledgements Thank you to my supervisor, Erik Rosolowsky, who ended up being stuck with me for the past 9 years at 2 different universities. First and foremost, thank you for being a constant source of advice throughout my studies, starting with a nervous first-year undergraduate over 9 years ago who really wanted to \do research" (without any clue what that meant), to today, and likely well into the future. I appreciate the freedom I have had to guide my research with your constant support, encouragement, and guidance. Over the past several years, I have had the opportunity to work with a won- derful group of collaborators, including several who have generously mentored me along the way. Thank you to Jason Loeppky, Stella Offner, Ryan Boy- den, Adam Ginsburg, Blakesley Burkhart, Amanda Kepley, Andreas Schruba, Jonathan Braine, Megan Johnson, Jay Lockman, SneˇzanaStanimirovi´c,and Julianne Dalcanton. A special thank you to the z0mgs collaboration, includ- ing Karin Sandstrom, J´er´emy Chastenet, I-Da Chiang, and Dyas Utomo, who have yet to kick me off their weekly telecons. And finally, thank you to Adam Leroy, who has been a mentor, collaborator, and host during my 3 month stay of The Ohio State University in 2019. Thank you to the many members of the Astrophysics Group at the Univer- sity of Alberta. First, thank you to my committee members, Dmitri Pogosyan and Gregory Sivakoff, for their guidance through my MSc and PhD. It has been a pleasure working with you for the past 6 years (and a summer). Dur- vii ing that time, I developed friendships with and had the opportunity to learn from my fellow graduate students and transient postdocs. Thank you in par- ticular to Alex Tetarenko, Bailey Tetarenko, Arash Bahramian, Kenny Van, Soumen Deb, Joseph Nofech, Maria Pettyjohn, Andrew Hughes, Zhuo Chen, Dario Colombo, and Veselina Kalinova. Thank you to my family for your love, encouragement, and support that have allowed me to follow my dreams. Most of all, thank you my wonderful and amazing Sarah. Words cannot express how much your constant love and support mean to me. viii Table of Contents 1 Introduction 1 1.1 The galactic ecosystem & baryonic cycle . 3 1.1.1 Converting gas to stars: the role of star formation . 4 1.1.2 Stellar death, feedback and enrichment . 10 1.1.3 Galaxies are not closed systems: inflow and outflow in galaxies . 11 1.2 Bridging the neutral ISM from extragalactic to Galactic scales with Local Group galaxies . 13 1.2.1 Modeling and interpretation of the HI line shape in nearby galaxies . 17 1.2.2 From HI to H2: kinematics of the neutral ISM in molec- ular cloud evolution . 30 1.2.3 Observational signatures of turbulent driving on galactic scales . 35 1.3 Outline & questions explored in this thesis . 41 2 A Modern 21-cm HI Survey of the Local Group 43 2.1 A basic overview of radio interferometry . 43 2.2 Historical ISM observations in the Local Group . 47 2.3 An L-band Local Group VLA survey . 48 2.3.1 Single-dish observations . 54 ix 2.3.2 VLA data reduction . 56 2.3.3 Techniques for imaging massive interferometric data . 58 2.3.4 Combining single-dish and interferometric observations 63 2.4 Summary . 66 3 Kinematics of the Atomic ISM in M33 on 80 pc scales 67 3.1 Introduction . 68 3.2 Observations . 72 3.2.1 VLA . 72 3.2.2 GBT . 72 3.3 Imaging & calibration . 74 3.3.1 Radio recombination lines . 74 3.3.2 H i imaging . 75 3.3.3 Signal masking .