Small-scale variations in the galactic magnetic field Rotation measure variations across extragalactic radio sources

Abstract

In order to explore small angular scale (⪉1arcmin) variations in Faraday rotation measure through the interstellar medium, the authors have observed 26 mostly 3C an 4C extended extragalactic radio sources at four frequencies between 1300 MHz and 5000 MHz using the VLA. Accurate rotation measures were sought for different components of each object to investigate the difference in rotation measure as a function of angular component separation. For most sources, the rms difference in rotation measure between components is ⪉10 rad m<SUP>-2</SUP> on angular scales &lt;10arcmin. However, for four sources in the galactic plane, the values are ΔRM ≈ 50 - 100 on a 0arcmin.1 - 1arcmin scale, which argues for enhanced turbulence somewhere along the line of sight.