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 $\sim 12\mathrm{deg}\times 12\mathrm{deg}$ ($\sim 1$kpc) around the Galactic Centre region. We show that the Galactic Plane for $|l|<10^{\circ }$ exhibits large Rotation Measures (RMs) with a maximum |RM| of $1691.2\pm 4.9\mathrm{rad}{\mathrm{m}}^{-2}$ and a mean $|\mathrm{RM}|=219\pm 42\mathrm{rad}{\mathrm{m}}^{-2}$. 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 components. 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 $0.83^{\circ }-11^{\circ }$ ($\sim 120-1500$ pc), which is expected for scales larger 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.

15+66 pages, 11+65 figures, 3 tables. In press with MNRAS

References in corpus (13)

• Dynamical modelling of the Galactic bulge and bar: the Milky Way's bar pattern speed, stellar, and dark matter mass distribution
• The outer scale of turbulence in the magneto-ionized Galactic interstellar medium
• The link between turbulence, magnetic fields, filaments, and star formation in the Central Molecular Zone cloud G0.253+0.016
• Estimating extragalactic Faraday rotation
• The effect of magnetic fields on star cluster formation
• Comparison of algorithms for determination of rotation measure and Faraday structure I. 1100 - 1400 MHz
• The Galactic Magneto-Ionic Medium Survey: Moments of the Faraday Spectra
• Magnetic field near the central region of the Galaxy: Rotation measure of extragalactic sources
• Extragalactic sources towards the central region of the Galaxy
• A Broadband Spectro-polarimetric View of the NVSS Rotation Measure Catalogue I: Breaking the nπ-ambiguity
• Polarization shadows of extragalactic sources by the local magneto-ionic ISM
• A Broadband Spectro-polarimetric View of the NVSS Rotation Measure Catalogue II: Effects of Off-axis Instrumental Polarisation
• Spatio-temporal evolution of the nonresonant instability in shock precursors of young supernova remnants

Cited by in corpus (2)

• Detection of magnetic fields in the circumgalactic medium of nearby galaxies using Faraday rotation
• A Radio Polarisation Study of Magnetic Fields in the Small Magellanic Cloud