Identification of plasma modes in Galactic turbulence with synchrotron polarization

TL;DR

This paper identifies plasma modes in Galactic turbulence using synchrotron polarization, providing observational evidence for magnetosonic modes' role in cosmic ray processes and highlighting their importance in interstellar phenomena.

Contribution

It presents the first observational diagnosis of plasma modes in various Galactic environments through synchrotron polarization analysis, linking turbulence properties to cosmic ray acceleration.

Findings

Magnetosonic modes are identified in different Galactic regions.

Correlation between gamma-ray excess and magnetosonic modes supports their role in cosmic ray scattering.

Results emphasize the importance of plasma properties in interstellar turbulence studies.

Abstract

Magneto-hydrodynamic (MHD) turbulence is ubiquitous and a fundamental ingredient underlying many astrophysical phenomena. The multiphase nature of interstellar medium and diversity of driving mechanisms give rise to spatial variation of turbulence properties, particularly their plasma properties. There has been no observational diagnosis of the plasma modes so far beyond the solar system. Here we report the identification of different plasma modes in various Galactic environments, including active star forming zones and supernova remnants, based on our synchrotron polarization analysis. The observed high degree of consistency between the $\gamma-$ray excess in Cygnus cocoon and the location of magnetosonic modes provides strong observational evidence for the long-advocated theory that magnetosonic modes dominate the cosmic ray (CR) scattering and acceleration. Our results open up a new avenue for the study of interstellar turbulence and demonstrate the indispensability to account for their plasma property in all the relevant processes including CR transport and star formation.