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Ghost of a shell: Magnetic fields of galactic supershell GSH 006 - 15 + 7


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Thomson, AJM, McClure-Griffiths, NM, Federrath, C, Dickey, JM ORCID: 0000-0002-6300-7459, Carretti, E, Gaensler, BM, Haverkorn, M, Kesteven, MJ and Staveley-Smith, L 2018 , 'Ghost of a shell: Magnetic fields of galactic supershell GSH 006 - 15 + 7' , Monthly Notices of the Royal Astronomical Society, vol. 479, no. 4 , pp. 5620-5637 , doi: 10.1093/mnras/sty1865.

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We identify a counterpart to a Galactic supershell in diffuse radio polarization, and use this to determine the magnetic fields associated with this object. GSH 006 - 15 + 7 has perturbed the polarized emission at 2.3 GHz, as observed in the S-band Polarization All Sky Survey (S-PASS), acting as a Faraday screen. We model the Faraday rotation over the shell, and produce a map of Faraday depth over the area across it. Such models require information about the polarized emission behind the screen, which we obtain from the Wilkinson Microwave Anisotropy Probe (WMAP), scaled from 23 to 2.3 GHz, to estimate the synchrotron background behind GSH 006 - 15 + 7. Using the modelled Faraday thickness, we determine the magnitude and the plane-of-the-sky structure of the line-of-sight magnetic field in the shell. We find a peak line-of-sight field strength of |B∥|peak = 2.0+0.01-0.7 μG. Our measurement probes weak magnetic fields in a low-density regime (number densities of ∼ 0.4cm-3) of the ISM, thus providing crucial information about the magnetic fields in the partially-ionized phase.

Item Type: Article
Authors/Creators:Thomson, AJM and McClure-Griffiths, NM and Federrath, C and Dickey, JM and Carretti, E and Gaensler, BM and Haverkorn, M and Kesteven, MJ and Staveley-Smith, L
Keywords: radio astronomy, polarisation, magnetic fields, bubbles
Journal or Publication Title: Monthly Notices of the Royal Astronomical Society
Publisher: Blackwell Publishing Ltd
ISSN: 0035-8711
DOI / ID Number: 10.1093/mnras/sty1865
Copyright Information:

Copyright 2018 The Authors. This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2018 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.

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