• DOI:10.1051/0004-6361/201323329
• Corpus ID: 62807237

Interstellar gamma-ray emission from cosmic rays in star-forming galaxies

@article{Martin2014InterstellarGE,
  title={Interstellar gamma-ray emission from cosmic rays in star-forming galaxies},
  author={Pierrick Martin},
  journal={Astronomy and Astrophysics},
  year={2014},
  volume={564}
}

• Pierrick Martin
• Published 3 February 2014
• Physics
• Astronomy and Astrophysics

Context. Fermi/LAT observations of star-forming galaxies in the∼0.1-100 GeV range have made possible a first population study . Evidence was found for a correlation between -ray luminosity and tracers of the star formation activity. Studying galactic cosmic rays (CRs) in various global conditions can yield information about their origin and transport in the interstellar medi um (ISM). Aims. This work addresses the question of the scaling laws that can be expected for the interstellar -ray emission as a function of global galactic properties, with the goal of establishing w hether the current experimental data in the GeV range can be constraining. Methods. I developed a 2D model for the non-thermal emissions from steady-state CR populations interacting with the ISM in star-forming galaxies. Most CR-related parameters were taken from Milky Way studies, and a large number of galaxies were then simulated with sizes from 4 to 40 kpc, several gas distributi ons, and star formation rates (SFR) covering six orders of magnitude. Results. The evolution of the -ray luminosity over the 100 keV-100 TeV range is presented, with emphasis on the contribution of the different emission processes and particle populations, and on the transition between transport regimes. The model can reproduce the normalisation and trend inferred from the Fermi/LAT population study over most of the SFR range. This is obtained with a plain diffusion scheme, a single diffusion coeffi cient, and the assumption that CRs experience large-scale volume-averaged interstellar conditions. There is, however, no universal relation between high-energy -ray luminosity and star formation activity, as illustrate d by the scatter introduced by different galactic global properties and the downturn in -ray emission at the low end. Conclusions. The current Fermi/LAT population study does not call for major modifications of the transport scheme for CRs in the Milky Way when extrapolated to other systems, probably because the uncertainties are still too large. Additional const raints may be expected from doubling the Fermi/LAT exposure time and later from observing at TeV energies with the Cherenkov Telescope Array .