Hadronic Production of Gamma Rays and Starburst Galaxies

TL;DR

This paper reviews gamma-ray production in the Milky Way and starburst galaxies, focusing on proton-proton interactions and modeling the resulting gamma-ray spectra, highlighting increased yields and spectral hardening in starburst environments.

Contribution

It introduces a model for calculating gamma-ray yields from starburst galaxies based on proton-proton interactions, accounting for higher fluxes and harder spectra.

Findings

Gamma-ray yield in starburst galaxies increases by 30-50%.

The gamma-ray spectrum becomes harder than the incident proton spectrum.

Proton-proton interactions dominate gamma-ray production in starburst galaxies.

Abstract

The Milky Way has been estabished to emit gamma rays. These gamma rays are presumably dominated by decays of neutral pions, although inverse Compton scatterings and bremsstrahlung also contribute. It is plausible that other galaxies can be diffuse sources of gamma rays in a similar manner. Starburst galaxies are particularly interesting to study as they are expected to have much higher cosmic-ray fluxes and interstellar matter densities. The neutral pions are created in cosmic-ray interactions with interstellar matter. Presented here is an overview of the recent work by Karlsson and co-workers on proton-proton interactions and the resulting secondary particle inclusive cross sections and angular distributions. This model can be used to calculated the $\pi^{0}$ component of the gamma-ray yield and spectrum from a starburst galaxy. The yield is expected to increase significantly (30% to 50%) and the spectrum to be harder than the incident proton spectrum.