Gamma-ray Constraints on Cosmic Rays in Galactic Winds

Type Conference Paper
Names Kaiqi Hu, J. E. Everett, E. G. Zweibel
Proceedings Title Bulletin of the American Astronomical Society
Conference Name American Astronomical Society, AAS Meeting #217, #241.19
Volume 43
Date January 1, 2011
Library Catalog NASA ADS
Abstract Our group is constructing a hybrid thermal gas and cosmic-ray pressure driven wind model. This model is built on past work by Breitschwerdt et al. (1991) and Zirakashvili et al. (1996), and was motivated by unexplained high latitude Galactic X-ray emission observed by ROSAT, and further tested with radio synchrotron observations. In this poster, the role of cosmic-ray protons in generating gamma-ray emission in a Galactic wind is explored. In interacting with the wind plasma, cosmic-ray protons have three mechanisms to generate gamma-rays (pion production, Bremsstrahlung, and inverse Compton scattering), which can be detected by the Fermi Gamma-ray Space Telescope. To test the model, we have calculated the gamma-ray intensity from the wind model of Everett et al (2010), and we compare these predictions to the observed emission in the central Milky Way. Also, we have recently developed a new wind model which includes an azimuthal magnetic field and galactic rotation; we compare the driving in this improved model to the previous one, and report on the gamma-ray emissivity of this model as well. In the future we will apply this model to other galaxies which are observed to have a large scale wind, such as M82 and NGC 253. Understanding the high latitude gamma-ray emission from relativistic particles in galactic winds may help to constrain dark-matter models as well. This work has been supported by NASA through grant NNX10AO50G, and by the NSF through grants NSF AST-0907837 and NSF PHY-0821899 (to the Center for Magnetic Self-Organization in Laboratory and Astrophysical Plasmas).
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