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UNIVERSITY of CALIFORNIA SANTA CRUZ MULTI-WAVELENGTH ASTROPHYSICAL PROBES of DARK MATTER PROPERTIES a Dissertation Submitted In

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UNIVERSITY of CALIFORNIA SANTA CRUZ MULTI-WAVELENGTH ASTROPHYSICAL PROBES of DARK MATTER PROPERTIES a Dissertation Submitted In UNIVERSITY OF CALIFORNIA SANTA CRUZ MULTI-WAVELENGTH ASTROPHYSICAL PROBES OF DARK MATTER PROPERTIES A dissertation submitted in partial satisfaction of the requirements for the degree of DOCTOR OF PHILOSOPHY in PHYSICS by Alex McDaniel June 2020 The Dissertation of Alex McDaniel is approved: Professor Tesla Jeltema, Chair Professor Stefano Profumo Professor Robert Johnson Quentin Williams Acting Vice Provost and Dean of Graduate Studies Copyright © by Alex McDaniel 2020 Table of Contents List of Figures vi List of Tables viii Abstract ix Dedication x Acknowledgments xi 1 Introduction 1 1.1 Discovery and Evidence for Dark Matter . .1 1.2 Dark Matter Properties and Candidates . .3 1.3 WIMP Dark Matter and Detection Methods . .5 1.4 Self Interacting Dark Matter and Small Scale Challenges . 10 1.5 Outline of the Dissertation . 14 2 Multiwavelength Analysis of Dark Matter Annihilation and RX- DMFIT 16 2.1 Introduction . 16 2.1.1 Background and Motivation . 16 2.2 Radiation From DM Annihilation . 20 2.2.1 Diffusion Equation . 20 2.2.2 Synchrotron . 23 2.2.3 Inverse Compton . 24 2.3 Parameter Selection . 25 2.3.1 Magnetic Field Model . 26 2.3.2 Dark Matter Profile . 28 2.3.3 Diffusion Parameters . 29 2.4 Application and Results . 30 2.4.1 Diffusion Effects . 30 2.4.2 Magnetic Fields . 36 iii 2.4.3 Dark Matter Constraints from Synchrotron Radiation . 39 2.5 Conclusion . 44 3 A Multi-Wavelength Analysis of Annihilating Dark Matter as the Origin of the Gamma-Ray Emission from M31 46 3.1 Introduction . 46 3.2 Astrophysical Modeling . 50 3.2.1 Diffusion . 50 3.2.2 Magnetic Field . 52 3.2.3 Dark Matter Density Profile . 53 3.2.4 Interstellar Radiation Field . 53 3.3 Emission from Dark Matter Annihilation . 55 3.3.1 Synchrotron . 55 3.3.2 Inverse Compton . 57 3.3.3 Gamma-rays . 58 3.4 Particle Physics Framework . 58 3.5 Results . 59 3.5.1 Compatibility with Galactic Center Excess Particle Models 59 3.5.2 Fitting the Mass and Cross-section to the Andromeda Gamma- ray Data . 63 3.5.3 Comparison to Radio Data . 64 3.6 Conclusion . 67 4 Exploring A Cosmic-Ray Origin of the Multi-wavelength Emis- sion in M31 71 4.1 Introduction . 71 4.2 Astrophysical Model of Andromeda . 75 4.2.1 Magnetic Field . 75 4.2.2 Inter-stellar Radiation Field . 76 4.2.3 Solution to the Diffusion Equation . 78 4.3 Multi-wavelength Emission . 80 4.3.1 Synchrotron Power . 81 4.3.2 Inverse Compton Power . 82 4.3.3 Gamma-ray Flux . 83 4.4 Gamma-ray and Radio Data . 83 4.5 Results . 84 4.5.1 Emission from primary cosmic ray electrons . 85 4.5.2 Emissions from cosmic rays of hadronic origin . 91 4.5.3 Multi-component cosmic ray source model . 96 4.6 Diffuse X-ray Emission in M31 . 101 4.7 Conclusion . 103 iv 5 X-Ray Shapes of Elliptical Galaxies and Implications for Self- Interacting Dark Matter 106 5.1 Introduction . 106 5.2 X-ray Emissivity as a Tracer of the Mass Distribution . 110 5.2.1 Gravitational Potential of an Ellipsoidal Mass Distribution 110 5.2.2 Hydrostatic Equilibrium – Gas Density and X-ray Emissivity111 5.3 Galaxy Sample and Data Reduction . 114 5.3.1 Galaxy Selection . 114 5.3.2 Observations and Data Reduction . 118 5.4 X-ray Ellipticity and Brightness Profiles . 120 5.5 Results . 121 5.5.1 Implications for the Cross-section of Dark Matter Interac- tions . 128 5.6 Conclusions . 130 6 Conclusion 139 Bibliography 144 v List of Figures 2.1 Dark Matter Annihilation SED in a “non-cool-core” and “cool-core” Cluster . 32 2.2 Dark Matter Annihilation in a dSph. 32 2.3 Dark Matter Annihilation in a “Normal” Galaxy . 33 2.4 dSph. with Varying Diffusion and b¯b annihilation . 34 2.5 dSph. with Varying Diffusion and W +W − annihilation . 35 2.6 Synchrotron and Inverse-Compton Spectra of the Cluster, dSph, and Galaxy Models . 37 2.7 SED of the Cluster, dSph, and Galaxy Models with Varying B0 . 38 2.8 Radio Constraints from Dark Matter Annihilation For Various An- nihilation Channels in Segue I . 41 2.9 Radio Constraints from Dark Matter Annihilation Segue I Com- pared to Fermi Constraints . 42 3.1 DM Induced Gamma Ray SED in M31 . 61 3.2 Model Cross-Sections for Various Annihliation Channels and Profile Contractions . 62 3.3 Gamma-Ray Cross-Section Contours for Best Fit to Fermi Data in M31 .................................. 64 3.4 Gamma-Ray SEDs for Best-fit and Fixed Particle Models . 65 vi 3.5 Multi-Wavelength SED of the Best-Fit DM Models . 66 3.6 Diffusion Effects on the Multi-Wavelength SED in M31 . 68 3.7 Magnetic Field Effects on the Multi-Wavelength SED in M31 . 68 4.1 Multi-wavelength SED from Primary CRe in M31 . 86 4.2 Multi-wavelength SED from CRe with Varying Magnetic Field . 88 4.3 CRe Power Injection in M31 . 91 4.4 Spectrum from CRp π0 decay with varying αp ........... 94 4.5 Multiwavelength SED of Secondary CRe . 95 4.6 CRp Power Injection Contours . 97 4.7 Best-Fit Cosmic Ray Induced Mulitwavelength SED in M31 . 99 4.8 Cosmic Ray Induced Mulitwavelength SED in M31 with Varying Parameters . 100 4.9 CRe and CRp Power Injection as a Function of Magnetic Field Strength . 102 5.1 Model X-ray Surface Brightness Profiles . 113 5.2 Model X-ray Ellipticity Profiles . 113 5.3 NGC 6482 Observations from Chandra and XMM . 132 5.4 Surface Brightness Profile and Background Model of IC 4451 . 133 5.5 Ellipticity Profiles of the Best-Fit NFW Models . 134 5.6 Surface Brightness Profiles of the Best-Fit NFW Models . 135 5.7 Ellipticty and Surface Brightness Profiles of IC 4956 . 136 5.8 Ellipticities for Each Galaxy and Mass Configurations . 137 5.9 Distribution of NFW Ellipticities Compared with Simulated Results 138 vii List of Tables 2.1 NFW Parameters for the Cluster dSph. and Galaxy Models. 28 2.2 Segue I Parameters . 40 3.1 Astrophysical Parameters of M31 . 55 3.2 Dark matter fit parameters for the gamma-ray emission in M31 . 60 4.1 Primary CRe Fit Parameters in M31 . 87 4.2 CRe Normalizations for Various Magnetic Field Strengths . 88 4.3 CRp Best fit Parameters . 94 4.4 Multi-component cosmic-ray model parameters for M31 . 98 5.1 Sample of Elliptical Galaxies . 115 5.2 X-ray Observations of Elliptical Galaxies . 116 5.3 X-ray Observations of Elliptical Galaxies (Cont.) . 117 5.4 XMM Fit Parameters . 125 5.5 XMM Fit Parameters (Cont.) . 126 5.6 Chandra Fit Parameters . 127 5.7 Chandra Fit Parameters (Cont.) . 128 viii Abstract Multi-wavelength Astrophysical Probes of Dark Matter Properties by Alex McDaniel Although we have yet to fully understand the nature of dark matter (DM), as- trophysical observations across the electromagnetic spectrum allow us to probe its properties and constrain proposed models. These include annihilating DM models that can be investigated through their standard model annihilation prod- ucts such as electrons and positrons that produce radio, X-ray, and gamma-ray emission through typical radiative processes such as synchrotron radiation and inverse compton scattering. Some other proposed DM models exhibit collisional self interactions that impact the shapes of DM haloes. Using X-ray observations, the DM halo shapes can be constrained in order to probe the strength of possible DM self interactions. In this dissertation, I present an overview of our work in the development of the RX-DMFIT tool to study the secondary emission from DM annihilation, along with applications to DM and cosmic ray studies in the Andromeda galaxy. I also discuss work using data from Chandra and XMM- Newton in studying the X-ray shapes of elliptical galaxies to constrain DM self interactions. ix To my family, especially my Mom and my Grandma Pat x Acknowledgments I would first like to start by thanking my advisor Tesla Jeltema, without whom this work would not have been possible. She has been a great resource of knowledge in astronomy and astrophysics, as well as generally how to navigate grad school and academia. I cannot thank her enough for the opportunities she has provided during my time in my graduate career, allowing me to perform exciting research and travel to conferences and summer schools. Her passion and dedication to supporting her students cannot be overstated, and her mentorship has been the driving force in helping me grow into a researcher and scientist. Thanks to Stefano Profumo, who has been an amazing collaborator and invaluable in accomplishing this work, while helping show me how to approach questions in physics in novel and creative ways. I would also like to thank Robert Johnson for serving on my dissertation committee, and the many graduate students here at UC Santa Cruz who have given me support and camaraderie over the years. My family of course has also been a major source of support throughout my life before and throughout grad school. I would like foremost to thank my mom Laurie for her unwavering support in everything that I have done. I would also like to especially thank my Aunt Lynda and Uncle Alan for all their help and support over the past five years. From helping me get settled in Santa Cruz in the first place, to being available for dinners and a place to stay over the hill, it has been great to have you nearby and made grad school more enjoyable.
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