# Diffuse Gamma Rays in 3D Galactic Cosmic-ray Propagation Models

## TL;DR

This paper uses the Picard code to model 3D Galactic cosmic ray propagation, revealing how spiral-arm structures influence diffuse gamma-ray emission, especially in the inverse-Compton channel, with significant differences from symmetric models.

## Contribution

It introduces high-resolution 3D cosmic ray propagation models incorporating spiral-arm structures, highlighting their impact on gamma-ray emission predictions compared to traditional symmetric models.

## Key findings

- Spiral-arm aligned source distributions affect gamma-ray emission patterns.
- Inverse-Compton emission shows distinct spiral-arm imprints.
- Differences between 3D and symmetric models are significant on global and local scales.

## 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.