Galactic diffuse emission in gamma-rays is predominantly due to cosmic rays producing neutral pions through nuclear interactions with the gas in the Galactic disk. Hence, the spatial distribution of atomic and molecular gas is crucial for reliable modelling of diffuse gamma-rays. Yet, analysis of gas line surveys suffer from various deficencies in reconstructing the 3D distribution. Here, we present a new method that cures some of these issues by using the correlation structure. We present the highest resolution 3D maps yet of molecular gas and give a short preview of ongoing work on the atomic gas map.
The distribution of gas also has important effects for the transport of cosmic rays. In the vicinity of their source cosmic rays will be self-confined due to the resonant streaming instability. The gas density features in determining the damping of the self-generated turbulence, but also in energy losses for cosmic ray nuclei. We have studied the transport around sources in the MeV-GeV regime and found significant modifications of the spatial, temporal and energy distributions of cosmic rays near their sources. Putting together all these different pieces of information will allow for more reliable models of cosmic rays.