The distribution of cosmic-ray sources in the Galaxy, γ-rays and the gradient in the CO-to-H2 relationA. W. Strong, I. V. Moskalenko, O. Reimer, S. Digel and R. DiehlA&A, 422 3 (2004) L47-L50DOI: https://doi.org/10.1051/0004-6361:20040172
