Galactic synchrotron emission with cosmic ray propagation models

TL;DR

This paper advances Galactic radio emission modeling by incorporating polarization, absorption, and free-free emission into the GALPROP code, comparing predictions with observational data to refine cosmic ray propagation and magnetic field understanding.

Contribution

It introduces new modeling features in GALPROP for radio emission, including polarization and absorption, and evaluates different cosmic ray and magnetic field configurations against observational data.

Findings

Anisotropic magnetic fields improve model-data agreement.

A halo size of 10 kpc is favored for accurate modeling.

Models successfully reproduce total intensity and polarization maps.

Abstract

Cosmic-ray (CR) leptons produce radio synchrotron radiation by gyrating in interstellar magnetic fields (B-field). Details of B-fields, CR electron distributions and propagation are still uncertain. We present developments in our modelling of Galactic radio emission with the GALPROP code. It now includes calculations of radio polarization, absorption, and free-free emission. Total and polarized synchrotron emission are investigated in the context of physical model of CR propagation. Predictions are compared with radio data from 22 MHz to 2.3 GHz, and Wilkinson Microwave Anisotropy Probe data at 23 GHz. Spatial and spectral effects on the synchrotron modelling with different CR distribution, propagation halo size and CR propagation models are presented. We find that all-sky total intensity and polarization maps are reasonably reproduced by including an anisotropic B-field, with comparable intensity to the regular one defined by rotation measures. A halo size of 10 kpc, which is larger than usually assumed, is favoured. This work provides a basis for further studies on foreground emission with the Planck satellite and on interstellar gamma-ray emission with Fermi-Large Area Telescope.