Synchrotron Constraints on a Hybrid Cosmic-Ray and Thermally-Driven Galactic Wind

TL;DR

This study refines a cosmic-ray and thermally-driven galactic wind model by comparing its synchrotron emission predictions with observations, leading to adjustments in the launching region, magnetic field strength, and wind parameters to better match multi-wavelength data.

Contribution

It introduces a revised wind model constrained by synchrotron observations, improving understanding of wind launching conditions and magnetic field effects in the Galactic center.

Findings

Revised wind model fits both radio and X-ray observations.

Lower magnetic field strength reduces cosmic-ray heating effects.

Higher gas pressure and temperature are needed in the revised model.

Abstract

Cosmic rays and magnetic fields can substantially impact the launching of large-scale galactic winds. Many researchers have investigated the role of cosmic rays; our group previously showed that a cosmic-ray and thermally-driven wind could explain soft X-ray emission towards the center of the Galaxy. In this paper, we calculate the synchrotron emission from our original wind model and compare it to observations; the synchrotron data shows that earlier assumptions about the launching conditions of the wind must be changed: we are required to improve that earlier model by restricting the launching region to the domain of the inner "Molecular Ring", and by decreasing the magnetic field strength from the previously assumed maximum strength. With these physically-motived modifications, we find that a wind model can fit both the radio synchrotron and the X-ray emission, although that model is required to have a higher gas pressure and density than the previous model in order to reproduce the observed X-ray emission measure within the smaller `footprint'. The drop in magnetic field also decreases the effect of cosmic-ray heating, requiring a higher temperature at the base of the wind than the previous model.