Title: Diffuse Gamma Rays in 3D Galactic Cosmic-ray Propagation Models,
Abstract: The Picard code for the numerical solution of the Galactic cosmic ray
propagation problem allows for high-resolution models that acknowledge the 3D
structure of our Galaxy. Picard was used to determine diffuse gamma-ray
emission of the Galaxy over the energy range from 100 MeV to 100 TeV. We
discuss the impact of a cosmic-ray source distribution aligned with the
Galactic spiral arms for a range of such spiral-arm models. As expected, the
impact on the gamma-ray emission is most distinct in the inverse-Compton
channel, where imprints of the spiral arms are visible and yield predictions
that are no longer symmetric to the rotational axis of the Milkyway. We will
illustrate these differences by a direct comparison to results from previous
axially symmetric Galactic propagation models: we find differences in the
gamma-ray flux both on global scales and on local scales related to the spiral
arm tangents. We compare gamma-ray flux and spectra at on-arm vs. off-arm
projections and characterize the differences to axially symmetric models.