Global cosmic-ray related luminosity and energy budget of the Milky Way

TL;DR

This study uses the GALPROP code to calculate the Milky Way's broad-band luminosity spectrum related to cosmic-ray propagation, revealing the galaxy's near-calorimetric behavior and its implications for diffuse emissions and extragalactic backgrounds.

Contribution

It provides a comprehensive calculation of the Milky Way's luminosity spectrum from cosmic-ray interactions, highlighting the galaxy's near-calorimetric nature and the relationship between radio and infrared emissions.

Findings

The Milky Way is nearly a cosmic-ray electron calorimeter when gamma-ray processes are included.

Synchrotron radiation accounts for about one third of total electron energy losses.

The model's FIR-radio luminosity relationship aligns with that observed in other galaxies.

Abstract

We use the GALPROP code for cosmic-ray (CR) propagation to calculate the broad-band luminosity spectrum of the Milky Way related to CR propagation and interactions in the interstellar medium. This includes gamma-ray emission from the production and subsequent decay of neutral pions, bremsstrahlung, and inverse Compton scattering, and synchrotron radiation. The Galaxy is found to be nearly a CR electron calorimeter, but {\it only} if gamma ray emitting processes are taken into account. Synchrotron radiation alone accounts for only one third of the total electron energy losses with ~10-20% of the total synchrotron emission from secondary CR electrons and positrons. The relationship between far-infrared and radio luminosity that we find from our models is consistent with that found for galaxies in general. The results will be useful for understanding the connection between diffuse emissions from radio through gamma rays in ``normal'' (non-AGN dominated) galaxies, as well as for estimating the broad-band extragalactic diffuse background from these kinds of galaxies.