The outer scale of turbulence in the magneto-ionized Galactic interstellar medium

Abstract

We analyze Faraday rotation and depolarization of extragalactic radio point sources in the direction of the inner Galactic plane to determine the outer scale and amplitude of the rotation measure power spectrum. Structure functions of rotation measure show lower amplitudes than expected when extrapolating electron density fluctuations to large scales assuming a Kolmogorov spectral index. This implies an outer scale of those fluctuations on the order of a parsec, much smaller than commonly assumed. Analysis of partial depolarization of point sources independently indicates a small outer scale of a Kolmogorov power spectrum. In the Galaxy's spiral arms, no rotation measure fluctuations on scales above a few parsecs are measured. In the interarm regions fluctuations on larger scales than in spiral arms are present, and show power law behavior with a shallow spectrum. These results suggest that in the spiral arms stellar sources such as stellar winds or protostellar outflows dominate the energy injection for the turbulent energy cascade on parsec scales, while in the interarm regions supernova and super bubble explosions are the main sources of energy on scales on the order of 100 parsecs.

14 pages, 6 figures, accepted by ApJ

References in corpus (5)

• Rotation Measures of Extragalactic Sources Behind the Southern Galactic Plane: New Insights into the Large-Scale Magnetic Field of the Inner Milky Way
• The Southern Galactic Plane Survey: Polarized Radio Continuum Observations and Analysis
• The spatial energy spectrum of magnetic fields in our Galaxy
• An improved solar wind electron-density model for pulsar timing
• Polarization shadows of extragalactic sources by the local magneto-ionic ISM

Cited by in corpus (2)

• The Turbulent Warm Ionized Medium: Emission Measure Distribution and MHD Simulations
• Simulating polarized Galactic synchrotron emission at all frequencies, the Hammurabi code