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On the interaction between cosmic rays and dark matter molecular clouds in the Milky Way – I. Basic considerations
Authors:D W Sciama
Institution:SISSA Via Beirut, 2-4, 34014 Trieste, Italy; ICTP, Strada Costiera, 11, 34014 Trieste, Italy; Nuclear and Astrophysics Laboratory, Keble Road, Oxford OX1 3RH
Abstract:We explore some basic observational consequences of assuming that the dark matter in the Milky Way consists mainly of molecular clouds, and that cosmic rays can penetrate these clouds. In a favoured model of the clouds, this penetration would have the following consequences, all of which agree with observation.
(i) Cosmic ray nuclei would be fragmented when they enter a cloud, giving them a lifetime in the Galaxy of ∼1015 s (for relativistic nuclei).
(ii) Pionic γ -rays emitted by the clouds, after proton–proton (pp) collisions, would have a diffuse flux in the Galactic plane comparable to the flux from known sources for photon energies ≳1 GeV .
(iii) The heat input into the clouds from cosmic rays would be re-radiated mainly in the far-infrared. The resulting radiation background agrees, in both intensity and spectrum in different directions, with a known excess in the far‐infrared background of the galaxy over emission by warm dust.
Keywords:ISM: clouds  cosmic rays  dark matter  gamma-rays: observations  infrared: ISM: continuum
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