High-energy emission from galaxies: the star-formation/gamma-ray connection

Abstract

Abstract. The impact of non-thermal processes on the spectral energy distributions of galaxies can be dramatic, but such processes are often neglected in considerations of their structure and evolution. Particle acceleration associated with high mass star formation and AGN activity not only leads to very broad band (radio-γ-ray) emission, but may also produce very significant feedback effects on galaxies and their environment. The recent detections of starburst galaxies at GeV and TeV energies suggest that γ-ray instruments have now reached the critical level of sensitivity to probe the connection between particle acceleration and star-formation in galaxies. In this paper we will try to summarise this recent progress, put it into a multi-wavelength context and also discuss the prospects for more precise and sensitive γ-ray measurements with the upcoming CTA observatory.

Starburst galaxies as seen by gamma-ray telescopes

“…An important ingredient in the modelling is the electron-to-proton (e/p) ratio, which is inferred from Galactic radio measurements and under the assumption of equipartition between magnetic fields and CRs, and is typically found to be 1/100 in the Milky Way. To illustrate the influence of different quantities on the radiation spectra, Figure 2b) shows two simple one-zone, time-dependent models for the continuous injection of electrons and protons over 200 kyrs in two representative starburst environments at 3.5 Mpc (see [30] for a detailed model description). The first model shows the SED for a starburst galaxy where IC losses in the strong radiation fields dominate over synchrotron emission (full lines).…”

“…To illustrate the influence of different quantities on the radiation spectra, Figure 2b) shows two simple one-zone, time-dependent models for the continuous injection of electrons and protons over 200 kyrs in two representative starburst environments at 3.5 Mpc (see [30] for a detailed model description). The first model shows the SED for a starburst galaxy where IC losses in the strong radiation fields dominate over synchrotron emission (full lines).…”