# The Physics of Galactic Winds Driven by Cosmic Rays I: Diffusion

**Authors:** Eliot Quataert, Todd A. Thompson, Yan-Fei Jiang  
**arXiv:** [2102.05696](https://arxiv.org/abs/2102.05696)  
**Date:** 2021-02-10  
**Summary page:** https://www.summarizepaper.com/en/paper/2102.05696v1/

## Key points

- Authors explore the physics of Cosmic Ray (CR) transport and its role in generating galaxy-scale outflows
- Focus on CR-driven galactic winds dominated by diffusion
- Comprehensive analysis supported by analytic calculations and simulations
- Winds exhibit energy flux comparable to that supplied to CRs for diffusion coefficients above a critical threshold, leading to rapid acceleration
- For lower diffusion coefficients, CR-driven winds experience slower acceleration and lose energy predominantly to gravity
- Predict mass-loss rates in these winds based on Fermi gamma-ray observations of pion decay
- Consistent mass-loss rates with star formation rates in dwarf and disc galaxies, but discrepancies with stellar and dark matter halo mass functions exist
- Nuclear starbursts like M82 and Arp 220 show significant impact of CR diffusion and pion losses on weakening CR pressure within galaxies and dampening strength of CR-driven winds
- Findings have implications for interpreting observations of galactic winds and understanding the involvement of CRs in shaping galaxy formation processes

## Summary

In this paper, the authors explore the intricate physics of Cosmic Ray (CR) transport and its role in generating galaxy-scale outflows. They focus on CR-driven galactic winds dominated by diffusion and present a comprehensive analysis supported by both analytic calculations and simulations. By considering diffusion coefficients above a critical threshold, they reveal that these winds exhibit an energy flux comparable to that supplied to CRs, leading to rapid acceleration. However, for lower diffusion coefficients, CR-driven winds experience slower acceleration and predominantly lose their energy to gravity. The authors also predict mass-loss rates in these winds based on Fermi gamma-ray observations of pion decay. While they are consistent with star formation rates in dwarf and disc galaxies, they fall short in reconciling discrepancies between stellar and dark matter halo mass functions. Additionally, nuclear starbursts such as M82 and Arp 220 demonstrate the significant impact of CR diffusion and pion losses on weakening CR pressure within galaxies and dampening the strength of CR-driven winds. These findings have implications for interpreting observations of galactic winds and shedding light on the involvement of CRs in shaping galaxy formation processes. Through a synthesis of analytical predictions with numerical simulations, this study provides valuable insights into the complex interplay between cosmic rays and galactic dynamics.