1. Optimizing Galaxy Simulations using FGST Observations
Andrew McLeod
SULI Presentation
August 13, 2009

2. GALPROP
Simulates the gamma ray and cosmic ray sky given a set of initial conditions and physical parameters
Allows a priori predictions to be compared to astronomical data

3. GALPROP
Method
Calculates a density field of cosmic rays given the distribution of cosmic ray sources (pulsars, supernova remnants) as an initial condition
Computes the interaction of these cosmic rays with the interstellar gas field, radiation field, and magnetic field

4. “Propagation of cosmic rays: nuclear physics in cosmic ray studies”, Igor V. Moskalenko
Source:
GALPROP

5. GALPROP
Predicted gamma ray sky from Bremsstrahlung near our solar system

6. GALPROP

7. The Project
Current parameter set optimized using EGRET data ( )
Optimize to new Fermi data
Simulated Fermi Data (>1 GeV, 1 yr)

8. GaDGET
Calculates how well GALPROP models fit gamma ray sky detected by Fermi
Fit-weights are computed for the energy bins of each component
Calculates model’s statistical likelihood
Produces sky-map of residual difference between fit-weight adjusted sky-map and Fermi data
These fit weights don’t artificially fine tune data; they indicate how simulations must be changed

9. GaDGET

10. Optimization GALPROP parameters can be varied Galactic Dimensions
Cosmic Ray Injection Spectra
Source Distribution
Diffusion Coefficient
~ 40 dimensional parameter space

11. Optimization Model Analysis (MAn) software developed for this project
Analysis settings defined in a specification file
Thirty-five different comparisons plotted
Many user-defined setting; easily adaptable for future model optimization

12. Optimization

13. Results
Previously used GALPROP parameters physically feasible, but not optimal
Current optimized parameters imply that
(relative to previous estimates):
The diffusion coefficient governing the propagation of cosmic rays depends more heavily on momentum
Cosmic ray source distribution peaks more sharply
Gamma ray producing processes can occur farther away from the galactic disk

14. Potential Applications
Indirect determination of Milky Way parameters
Better understand the processes by which cosmic rays propagate
Study extragalactic gamma ray spectrum

15. Acknowledgments
I would like to express my deep gratitude to my mentor, Markus Ackermann, for helping me define and carry out this project, as well as to my co-workers Josh Lande and Keith Bechtol who helped in its implementation.
Also, thanks to Steve Rock, SueVon Gee, Vivian Lee, and Elizabeth Smith for their stewardship of the SULI program.
Finally, thanks to the DOE Office of Science and SLAC for sponsoring the SULI program.

16. Works Cited
Moskalenko, Igor. “Modeling of the Galactic diffuse continuum gamma-ray emission” 6th INTEGRAL Workshop, Moscow, Russia
Moskalenko, Igor. “Propagation of Cosmic Rays and Diffuse Galactic Gamma Rays” Nuclear Data for Science and Technology, Santa Fe, New Mexico
Strong, Andrew. “GALPROP: a Cosmic-ray propagation and Gamma-ray code” Tools for SUSY, Annecy, France