Modeling Large-Scale Magnetic Fields in the Milky Way - ESA

Arm modulation?• Model of shock compression in spiral arms predicts roughly a factor of four ratiobetween pre- and post-shock for the component of the fields parallel to the shock,for the gas and dust, and at least that for the CREs.• This is not observed in synchrotron in external galaxies (e.g. M51) but it’s not clearwhether the observations have the resolution given that the shock region could befairly narrow.• CRE sources are also not uniformly distributed, and the CREs may remain highlyinhomogeneous if the diffusion is highly anisotropic. Two effects, one in shock and onedownstream, effectively smoothing it out?M51 and field by Fletcher et al. (2011)T. Jaffe @ ESAC, 30 May 2013Effenberger et al. (2012)