DARK MATTER DENSITY PROFILES OF HALOS IN THE ILLUSTRIS SIMULATION A Thesis submitted to the faculty of San Francisco State University As In partial fulfillment of the requirements for ^ u the Degree pH Vs Masters of Science ' M3 3 In Physics: Astronomy by Daniel Frederick McKeown Jr. San Francisco, California Spring, 2017 Copyright by Daniel Frederick McKeown Jr. 2017 CERTIFICATION OF APPROVAL I certify that I have read Dark Matter Density Profiles Of Halos In The Illustris Simulation by Daniel Frederick McKeown, and that in my opinion this work meets the criteria for approving a thesis submitted in partial fulfillment of the requirement for the degree Master of Science in Physics: Astronomy at San Francisco State University. Andisheh Mahdavi, Ph.D. Associate Professor Of Physics Adrienne Cool, Ph.D. Professor Of Physics Stephen Kane, Ph.D. Associate Professor Of Physics DARK MATTER DENSITY PROFILES OF HALOS IN THE ILLUSTRIS SIMULATION Daniel Frederick McKeown San Francisco, California 2017 We conduct a detailed study of the evolution of dark matter density as a function of radius for the most massive galaxy halos in the Illustris Simulation. The dark matter density profiles of these clusters are fit using a generalized NFW function. With the tree structure of Illustris, each halo is traced back to its progenitor across many redshifts, gaining insights into the evolution of the profile parameters as a function of cosmic time and halo environment throughout the merger history. The power law value from the NFW function is plotted as a function of dark matter mass as well as dark matter percentage and compared to its progenitors, as is the total halo mass and dark matter percentage. We uncover correlations in the relationships among these parameters within individual halo tree histories. These correlations indicate that the process of hierarchical structure formation through mergers, while largely dependent on the initial conditions of each halo, does follow broader trends whose explanation we reserve for future work. I certifi (presentation of the content of this Thesis. 5/18/2017 Chair, Thesis Committee Date ACKNOWLEDGEMENTS ACKNOWLEDGEMENTS I would like to thank the creators of Illustris, who created an outstanding and novel API for analyzing and interacting with their simulation, and which greatly improved upon the time required for analysis, in allowing for a much more rapid means to access data than would otherwise have been possible. I am greatly thankful to my thesis advisor and mentor, Dr. Andisheh Mahdavi, who introducing me to this project, and who played a big role in shaping my development into a scientist. I would also like to thank my wife and son for their love and support. v TABLE OF CONTENTS List of Tables...................................................................................................................... vii List of Figures....................................................................................................................viii List of Figures.......................................................................................................................ix Introduction............................................................................................................................1 Analysis and Procedure.........................................................................................................6 Massive Galaxy Profiles......................................................................................................15 Time Evolution of Halos.....................................................................................................23 Correlations Between DM Matter Density, Percent DM, Overall Mass of Halos.............28 Interpretation Of Results and Motivations for Future Investigations................................42 Conclusion...........................................................................................................................49 References............................................................................................................................51 LIST OF TABLES Table Page 1. Important Quantities of Interest for Halos in Illustris.............................................9 2. Values for NFW Fits for Massive Halos At Snap 135...........................................18 vii LIST OF FIGURES Figures Page 1. Neutral Hydrogen......................................................................................................5 2. Visible Luminosity Profiles In Illustris..................................................................... 5 3. Logical Progression Of The Main Program.............................................................. 8 4. Dark Matter Density of Halo 0 At Redshift 0...........................................................16 5. Dark Matter Density of Halo 3005 At Redshift 0.................................................... 17 6. Dark Matter Density of Halo 14767 At Redshift (0.169).........................................20 7. Goodness of Fit For Massive Halos...................................................................21 8. Powerlaw Vs. Goodness of Fit For Related Halos Across Redshifts.....................22 9. Power Law, DM Mass, DM Percent VS TIME of Halo 0 and Progenitors 23 10. Power Law, DM Mass, DM Percent VS TIME of Halo 3005 and Progenitors ....24 11. Power Law, DM Mass, DM Percent VS TIME of Halo 2130 land Progenitors ...25 12. Power Law, DM Mass, DM Percent VS TIME of Halo 13786 and Progenitors ..26 13. Power Law Vs. Dark Matter Mass of Halo 0 and Progenitors ..............................29 14. Power Law Vs. Dark Matter Mass of Halo 5317 and Progenitors.........................30 15. Power Law Vs. Dark Matter Mass of Halo 17407 and Progenitors........................31 16. Linear Correlation: Power Law Value Vs. Dark Matter Mass................................32 17. Power Law Vs. Dark Matter Percentage of Halo 13786 and Progenitors..............33 18. Power Law Vs. Dark Matter Percentage of Halo 16352 and Progenitors..............34 19. Power Law Vs. Dark Matter Percentage of Halo 20191 and Progenitors..............35 20. Linear Correlation: Power Law Value Vs. Dark Matter Percent.............................36 21. Total Mass Vs. Dark Matter Percentage of Halo 0 and Its Progenitors..................37 LIST OF FIGURES Figures Page 22. Total Mass Vs. Dark Matter Percentage of Halo 10299 and Its Progenitors 38 23. Total Mass Vs. Dark Matter Percentage of Halo 13786 and Its Progenitors 39 24. Total Mass Vs. Dark Matter Percentage of Halo 12430 and Its Progenitors 39 25. Linear Correlation: Dark Matter Percent Vs. Dark Matter Mass............................40 26. Mass Vs. DM Percent of 10,000 Halos....................................................................43 27. Densities of Halo 7062 At Redshift 134...................................................................45 28. Zoomed In: Densities of Halo 7062 At Redshift 134..............................................46 29. Zoomed In: Densities of Halo 7062 At Redshift 134..............................................47 1 I. INTRODUCTION BACKGROUND Since the discovery of distant stars orbiting on the outskirts of galaxies at velocities much greater than the visible matter they encircled would suggest by Vera Rubin, Kent Ford and others, this strange gravitating mass that does not interact electromagnetically has been found to not only be a real component of the cosmos, but to also to be the primary matter component (Rubin et al 1970). Given that it is the largest gravitating mass energy source of the cosmos, we expect dark matter to play a dominant role in shaping the structure and formation of galaxies on the large scale of galaxy clusters. Galaxy Clusters are among the most massive objects that we observe, and are believed to have formed from a hierarchy of mergers where galaxies combine as a result of gravitational interactions to form groups. Our own local group is one such cluster. These processes make galaxy clusters some of the youngest gravitationally bound structures in the cosmos, given that they have undergone mergers since the beginning and in their present state represent the longest evolutionary progression (Poole et al 2006). The composition of clusters, their components of stars, dark matter, and gas, provide a wealth of information about the underlying structure of our Universe. As the primary component of mass energy, composing approximately 85% of all known mass energy, dark matter is believed to be a dominant driver of the hierarchy of mergers. Its location, inferred from a variety of methods, in particular by detecting weak gravitational lensing shear, is found in halos that extend hundreds of kiloparsecs beyond the star rich centers, and on the large scale, dark matter is believed to be contained in web like structures connecting galaxies and pulling them together, serving as invisible yet dominant gravitational glue that plays a major role in the evolution of cluster formation (Kaiser etal 1986). 2 Of note, advancements in X-ray astronomy using the Chandra Space Telescope have greatly increased knowledge of galaxy clusters, from their scaling relations, their mass, to their physical structures and baryonic components, in particular, gas mass, which has been found to be a robust indicator for weak lensing (Mahdavi et al 2013). An example of the value in Chandra observations, is that it was successfully used along with CFHT weak gravitational lensing data to obtain several