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Discerning the Difficult-To-Detect: Star Formation in Dwarf and Low Surface Brightness Galaxies

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Discerning the Difficult-To-Detect: Star Formation in Dwarf and Low Surface Brightness Galaxies DISCERNING THE DIFFICULT-TO-DETECT: STAR FORMATION IN DWARF AND LOW SURFACE BRIGHTNESS GALAXIES By ANNA CHARLENE WRIGHT A dissertation submitted to the School of Graduate Studies Rutgers, The State University of New Jersey in partial fulfillment of the requirements for the degree of Doctor of Philosophy Graduate Program in Physics and Astronomy written under the direction of Alyson Brooks and approved by New Brunswick, New Jersey October, 2020 ABSTRACT OF THE DISSERTATION Discerning the Difficult-to-Detect: Star Formation in Dwarf and Low Surface Brightness Galaxies By ANNA CHARLENE WRIGHT Dissertation Director: Alyson Brooks In this work, we use cosmological simulations to study patterns of star formation in galaxies that have traditionally been underrepresented in surveys of galaxy formation across cosmic history. Because simulations have typically not been tuned to produce them, dwarf galaxies and low surface brightness galaxies provide a unique opportunity to test whether or not the models that we use to make bright, high mass galaxies are universal. We find that our simulations are able to reproduce a broad range of dwarf galaxy star formation histories, as well as low surface brightness galaxies, and we use these results to interpret the origin of specific types of galaxies. We identify a population of star-forming dwarf galaxies in our simulations that have experienced long periods of little to no star formation and whose properties are consistent with several dwarf galaxies observed in the local universe. We find that star formation can be reignited in these galaxies even billions of years after a quenching event through interactions with streams of gas in the intergalactic medium that compress hot halo gas. We also identify large populations of ultra-diffuse and classical low surface brightness galaxies in our simulations. Their properties are broadly consistent with ii those of observed samples and we predict that future observations will find that the star formation rates, HI masses, and colors of isolated ultra-diffuse galaxies are typical for their stellar masses. We find that both ultra-diffuse galaxies and classical low surface brightness galaxies are the products of major mergers that increase their angular momentum and cause star formation within the galaxies to move outward. In general, we find that environmental interactions have a significant impact on star formation in dwarf and low surface brightness galaxies - even those that appear isolated at the present day. iii Acknowledgments I am extremely grateful to my advisor, Alyson Brooks, whose patience, wisdom, and editing prowess have been truly invaluable. I am lucky enough to have a network of mentors that also includes Ferah Munshi, Michael Tremmel, Eric Gawiser, Curtis McCully, and Jillian Bellovary, who have all taken the time to guide and encourage me. I am deeply indebted to my friends and Rutgers co-workers - especially Sheehan Ahmed, Carl Mitchell, Jon Sloane, Jesse Rivera, Elaad Applebaum, Ray Sharma, and Charlotte Olsen - who have been a con- sistent source of laughter and support over the last 6 years. Finally, I am endlessly grateful for my husband, Jimmy Juno, whose unfailing optimism, kindness, and love are the foun- dations upon which I build all that I do. Chapter 2 of this thesis was adapted from “Reignition of Star Formation in Dwarf Galax- ies” by Anna C. Wright, Alyson M. Brooks, Daniel R. Weisz, and Charlotte R. Christensen. This article was published in Volume 482 of Monthly Notices of the Royal Astronomical Society. Chapter 3 of this thesis was adapted from “The Formation of Isolated Ultra-Diffuse Galaxies in Romulus25” by Anna C. Wright, Michael Tremmel, Alyson Brooks, Ferah Munshi, Daisuke Nagai, and Ray S. Sharma. This article has been submitted to Monthly Notices of the Royal Astronomical Society. The work presented in this thesis was supported by a Graduate Assistance in Areas of National Need fellowship, the Noemie Koller Endowed Scholarship, an ACM SIGHPC/Intel Computational & Data Science fellowship, Hubble Grant HST-AR-14281, and a PRAC allocation by the National Science Foundation (award number OAC-1613674). Resources supporting this work were provided by the NASA High-End Computing (HEC) Program iv through the NASA Advanced Supercomputing (NAS) Division at Ames Research Center and the Blue Waters sustained-petascale computing project, which is supported by the National Science Foundation (awards OCI-0725070 and ACI-1238993) and the state of Illinois. v Dedication For my husband, Jimmy, and our best friend, Callie vi Table of Contents Abstract :::::::::::::::::::::::::::::::::::::::::: ii Acknowledgments :::::::::::::::::::::::::::::::::::: iv Dedication ::::::::::::::::::::::::::::::::::::::::: vi List of Tables ::::::::::::::::::::::::::::::::::::::: ix List of Figures :::::::::::::::::::::::::::::::::::::: x 1. Introduction ::::::::::::::::::::::::::::::::::::: 1 1.1. Star Formation in Dwarf Galaxies . .1 1.2. A Brief History of Low Surface Brightness Galaxies . .6 1.3. Cosmological Simulations . .9 2. Reignition of Star Formation in Dwarf Galaxies ::::::::::::::: 13 2.1. Introduction . 13 2.2. The Simulations . 15 2.3. Results . 19 2.4. Observational Signatures . 35 2.5. Summary . 40 3. Ultra-diffuse Galaxies :::::::::::::::::::::::::::::::: 43 3.1. Introduction . 43 3.2. The Romulus25 Simulation . 46 vii 3.3. Results . 49 3.4. Comparison to HUDS . 80 3.5. Summary . 83 4. Classical Low Surface Brightness Galaxies ::::::::::::::::::: 86 4.1. Introduction . 86 4.2. Results . 90 4.3. Summary . 118 5. Summary and Future Outlook :::::::::::::::::::::::::: 120 Appendix A. Resolution :::::::::::::::::::::::::::::::: 124 Bibliography ::::::::::::::::::::::::::::::::::::::: 127 viii List of Tables 2.1. Properties of simulated dwarf galaxies . 16 3.1. Fraction of isolated dwarf galaxies that are ultra-diffuse . 52 ix List of Figures 2.1. Stellar mass – halo mass for dwarf galaxies . 20 2.2. Cumulative star formation histories for dwarf galaxies . 21 2.3. Evolution of virial mass for dwarf galaxies . 22 2.4. Gas masses, gas accretion rates, and star formation histories for dwarf galaxies 23 2.5. Time series of interaction between h986b and expanding shock wave . 28 2.6. Large-scale image of interaction between h986c and gas stream . 29 2.7. Small-scale time series of interaction between h986c and gas stream . 30 2.8. Comparison of simulated dwarf galaxies to Local Group dwarf galaxies . 37 2.9. Comparison of simulated dwarf galaxies to Local Volume dwarf galaxies . 41 3.1. Sample surface brightness profiles and mock UVI images of isolated UDGs and dwarf galaxies . 51 3.2. Distributions of sizes and surface brightnesses for isolated galaxies . 53 3.3. Distribution of Sérsic indices for isolated ultra-diffuse and dwarf galaxies . 56 3.4. Stellar mass - halo mass relation for low-mass galaxies . 57 3.5. HI masses of isolated ultra-diffuse and dwarf galaxies . 59 3.6. Star formation rates of isolated ultra-diffuse and dwarf galaxies . 60 3.7. Evolution of central surface brightness in isolated ultra-diffuse and dwarf galaxies . 62 3.8. Evolution of effective radius in isolated ultra-diffuse and dwarf galaxies . 63 3.9. Evolution of central specific star formation rate in isolated ultra-diffuse and dwarf galaxies . 65 x 3.10. Evolution and distribution of spin in isolated ultra-diffuse and dwarf galaxies 67 3.11. Correlation between spin and effective radius and central surface brightness in isolated ultra-diffuse and dwarf galaxies . 69 3.12. Distribution of time that has elapsed since the last major merger in isolated ultra-diffuse and dwarf galaxies . 71 3.13. Evolution of central surface brightness, effective radius, central specific star formation rate, and total spin relative to the time of the last major merger in isolated ultra-diffuse and dwarf galaxies . 72 3.14. Distribution of merger configurations in isolated ultra-diffuse and dwarf galaxies 78 3.15. Comparison of Romulus25 isolated ultra-diffuse and dwarf galaxies to ob- served sample of HI-bearing Ultra-Diffuse galaxies (HUDs) . 82 4.1. Sample surface brightness profiles and mock UVI images of classical LSB galaxies . 92 4.2. Fraction of galaxies that are classical LSB galaxies as a function of stellar mass 93 4.3. HI masses of classical LSB galaxies . 95 4.4. Star formation rates of classical LSB galaxies . 96 4.5. Cumulative star formation histories of classical LSB galaxies and HSB galaxies 97 4.6. Star formation rate and HI profiles of classical LSB galaxies and HSB galaxies 99 4.7. Star formation rate profiles of classical LSB galaxies and HSB galaxies scaled by scale length . 101 4.8. Distributions of colors and metallicities of classical LSB galaxies and HSB galaxies . 104 4.9. Colors of classical LSB galaxies as a function of recent changes in star forma- tion rate and metallicity . 105 4.10. Number of galaxies within a given radius of classical LSB galaxies and HSB galaxies . 108 xi 4.11. Distributions of numbers of satellites and distances to nearest neighbor for classical LSB galaxies and HSB galaxies . 109 4.12. Fraction of current mass of classical LSB galaxies and HSB galaxies relative to peak mass . 111 4.13. Stellar mass – halo mass relation for all central galaxies in Romulus25 ... 111 4.14. Distributions of time that has elapsed since the last major merger for classical LSB galaxies and HSB galaxies . 113 4.15. Evolution of HI-richness, location of star formation, gas spin, and total spin relative to the time of the last major merger in classical LSB galaxies and HSB galaxies . 115 4.16. Distributions of merger orientations and orbital angular momenta for classical LSB galaxies and HSB galaxies . 117 A.1. Evolution of gas masses in stripped and gappy dwarf galaxies . 125 A.2. Gas mass, gas accretion rate, and star formation history of h516a . 125 xii 1 Chapter 1 Introduction Our understanding of galaxy formation and evolution has historically been largely based upon the galaxies that emit the most light – the big and the bright. Unfortunately, this does not describe the majority of the galaxy population. Small, faint galaxies are much more common than the behemoths that are easiest to spot.
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