Mapping the gamma-ray distributions of the Magellanic Clouds

gamma rays;cosmic rays;Magellanic Clouds

Foreman, Gary James

关键词: gamma rays;    cosmic rays;    Magellanic Clouds;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/90459/FOREMAN-DISSERTATION-2016.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

The Large Area Telescope aboard the Fermi Gamma-ray Space Telescope is the first gamma-ray detector to observe external star forming galaxies with high enough significance to allow for spatial modeling of their gamma-ray distributions. Detections of the Milky Way by the Energetic Gamma Ray Experiment Telescope caused a boom in the field of gamma-ray spatial modeling and cosmic-ray simulation. Fermi has now set the stage for advancement in this field with the ability to test cosmic-ray physics in environments quite different from our own galaxy.In this work, I perform spatial analyses of the Fermi detections of the Milky Way satellites, the Large and Small Magellanic Clouds. Spatial maps used to compare to the Fermi signals are constructed based on three cosmic-ray particle interactions expected to generate gamma rays of energies detectable by Fermi: neutral pion production, bremsstrahlung radiation, and inverse Compton scattering. Maps derived from observations at longer wavelengths are used as tracers of the target particle distributions across the two galaxies: interstellar hydrogen (pion production and bremsstrahlung) and the interstellar radiation field (inverse Compton). I also consider two limiting cases for the cosmic-ray distributions: a concentrated case in which cosmic rays are traced by maps of star formation rates and a diffuse case that assumes cosmic-ray isotropy across the galaxies.To test the robustness of my spatial models, I introduce two statistical techniques not previously employed for Fermi data analysis: photon bootstrapping (LMC) and cross validation (SMC). For the larger, brighter LMC, I have used the spatially integrated energy spectrum to determine the contributions of each cosmic-ray collision process to the detected signal. Finally, in anticipation of advancements in cosmic-ray simulations based on the Fermi observations of the LMC, I lay the foundation for a dynamical model of the LMC in which to test cosmic-ray physics.