Heightened Faraday Complexity in the inner 1 kpc of the Galactic Centre

Abstract

We have measured the Faraday rotation of 62 extra-galactic background sources in 58 fields using the CSIRO Australia Telescope Compact Array (ATCA) with a frequency range of 1.1 - 3.1 GHz with 2048 channels. Our sources cover a region similar to 12 deg x 12 deg (similar to 1kpe) around the Galactic Centre region. We show that the Galactic Plane for vertical bar l vertical bar < 10 degrees exhibits large Rotation Measures (RMs) with a maximum vertical bar RM vertical bar of 1691.2 +/- 4.9 rad m(-2) and a mean vertical bar RM vertical bar 219 +/- 42 rad m(-2). The RMs decrease in magnitude with increasing projected distance from the Galactic Plane, broadly consistent with previous findings. We find an unusually high fraction 95(%) of the sources show Faraday complexity consistent with multiple Faraday component. We attribute the presences of multiple Faraday rotating screens with widely separated Faraday depths to small-scale turbulent RM structure in the Galactic Centre region. The second order structure function of the RM in the Galactic Centre displays a line with a gradient of zero for angular separations spanning 0.83 degrees - 11 degrees (similar to 120 - 1500 pc), which is expected for scales lager than the outer scale (or driving scale) of magneto-ionic turbulence. We place an upper limit on any break in the SF gradient of 66 '', corresponding to an inferred upper limit to the outer scale of turbulence in the inner 1 kpc of the Galactic Centre of 3 pc. We propose stellar feedback as the probable driver of this small-scale turbulence. Show more