Simulating Radio Synchrotron Morphology, Spectra, and Polarization of Cosmic Ray Driven Galactic Winds

TL;DR

This paper demonstrates that advanced cosmic ray transport simulations can accurately reproduce the radio morphology, spectra, and polarization of galactic winds in edge-on galaxies, providing insights into galaxy evolution.

Contribution

It introduces a state-of-the-art cosmic ray transport model in galaxy simulations that successfully matches observed radio features of NGC 4217.

Findings

Simulated radio intensity profiles agree with observations despite parameter degeneracies.

Radio spectra above 0.1 GHz match observed data and are weakly sensitive to magnetic field strength.

Magnetic fields exhibit X-shaped morphology consistent with observed galactic outflows.

Abstract

The formation of galaxies is significantly influenced by galactic winds, possibly driven by cosmic rays due to their long cooling times and better coupling to plasma compared to radiation. In this study, we compare the radio observations of the edge-on galaxy NGC 4217 from the CHANG-ES collaboration catalog with a mock observation of an isolated galaxy based on the arepo simulation that adopts the state-of-the-art two-moment cosmic ray transport treatment and multiphase interstellar medium model. We find significant agreement between the simulated and observed images and spectroscopic data for reasonable model parameters. Specifically, we find that (i) the shape of the intensity profiles depends weakly on the magnitude of the magnetic field, the distance of the simulated galaxy, and the normalization of the CR electron spectrum. The agreement between the mock and actual observations is degenerate with respect to these factors; (ii) the multi-wavelength spectrum above 0.1 GHz is in agreement with the radio observations and its slope is also only weakly sensitive to the magnetic field strength; (iii) the magnetic field direction exhibits X-shaped morphology, often seen in edge-on galaxies, which is consistent with the observations and indicates the presence of a galactic-scale outflow. Our results highlight the importance of incorporating advanced cosmic ray transport models in simulations and provide a deeper understanding of galactic wind dynamics and its impact on galaxy evolution.