Radio Synchrotron Fluctuation Statistics as a Probe of Magnetized Interstellar Turbulence

TL;DR

This study explores how synchrotron intensity fluctuations can reveal the sonic and Alfvénic Mach numbers of interstellar turbulence, highlighting the potential of polarization measurements with future radio telescopes.

Contribution

It introduces new statistical diagnostics for interstellar turbulence using synchrotron data and discusses how polarization can resolve observational degeneracies.

Findings

Structure function slope depends on Alfvénic Mach number

Integrated quadrupole ratio modulus indicates anisotropy

Polarization analysis can break degeneracy in magnetic field orientation

Abstract

We investigate how observations of synchrotron intensity fluctuations can be used to probe the sonic and Alfv\'enic Mach numbers of interstellar turbulence, based on mock observations performed on simulations of magnetohydrodynamic turbulence. We find that the structure function slope, and a diagnostic of anisotropy that we call the integrated quadrupole ratio modulus, both depend on the Alfv\'enic Mach number. However, these statistics also depend on the orientation of the mean magnetic field in the synchrotron emitting region relative to our line of sight, and this creates a degeneracy that cannot be broken by observations of synchrotron intensity alone. We conclude that the polarization of synchrotron emission could be analyzed to break this degeneracy, and suggest that this will be possible with the Square Kilometre Array.