Stochasticity of Cosmic Rays from Supernova Remnants and the Ionization Rates in Molecular Clouds

RWTH Publications (RWTH Aachen)

Abstract

Cosmic rays are the only agent able to penetrate into the interior of dense molecular clouds. Depositing (part of) their energy through ionisation, cosmic rays play an essential role in determining the physical and chemical evolution of star-forming regions. To a first approximation their effect can be quantified by the cosmic-ray induced ionization rate. Interestingly, theoretical estimates of the ionization rate assuming the cosmic-ray spectra observed in the local interstellar medium result in an ionization rate that is one to two orders of magnitude below the values inferred from observations. However, due to the discrete nature of sources, the local spectra of MeV cosmic rays are in general not representative for the spectra elsewhere in the Galaxy. Such stochasticity effects have the potential of reconciling modelled ionization rates with measured ones. Here, we model the distribution of low-energy cosmic-ray spectra expected from a statistical population of supernova remnants in the Milky Way. The corresponding distribution for the ionization rate is derived and confronted with data. We find that the stochastic uncertainty helps with explaining the surprisingly high ionization rates observed in many molecular clouds.

Authors 4

1. Vo Hong Minh Phan
2. Sarah Recchia

   Istituto Nazionale di Fisica Nucleare · Istituto Nazionale di Fisica Nucleare, Sezione di Torino · University of Turin

   Affiliation as printed

   Dipartimento di Fisica , Universitá di Torino , via P. Giuria 1 , 10125 Torino , Italy

   Istituto Nazionale di Fisica Nucleare , via P. Giuria , 1 , 10125 Torino , Italy

3. Philipp Mertsch Aachen Institute for Theoretical Particle Physics and Cosmology

   RWTH Aachen University

   Affiliation as printed

   Institute for Theoretical Particle Physics and Cosmology (TTK) , RWTH Aachen University , 52056 Aachen , Germany

4. S. Gabici

   Centre National de la Recherche Scientifique · Université Paris Cité

   Affiliation as printed

   Université de Paris , CNRS , Astroparticule et Cosmologie , F-75006 Paris , France