Properties of Nearby Starburst Galaxies Based on their Diffuse Gamma-ray Emission

Understand

The physical relationship between the far-infrared and radio fluxes of star forming galaxies has yet to be definitively determined.

• The favored interpretation, the "calorimeter model," requires that supernova generated cosmic ray (CR) electrons cool rapidly via synchrotron radiation.
• However, this cooling should steepen their radio spectra beyond what is observed, and so enhanced ionization losses at low energies from high gas densities are also required.
• Further, evaluating the minimum energy magnetic field strength with the traditional scaling of the synchrotron flux may underestimate the true value in massive starbursts if their magnetic energy density is comparable to the hydrostatic pressure of their disks.