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    Thermal plasma in the giant lobes of the radio galaxy Centaurus A

    Access Status
    Open access via publisher
    Authors
    O'Sullivan, S.
    Feain, I.
    McClure-Griffiths, N.
    Ekers, Ronald
    Carretti, E.
    Robishaw, T.
    Mao, S.
    Gaensler, B.
    Bland-Hawthorn, J.
    Stawarz
    Date
    2013
    Type
    Journal Article
    
    Metadata
    Show full item record
    Citation
    O'Sullivan, S. and Feain, I. and McClure-Griffiths, N. and Ekers, R. and Carretti, E. and Robishaw, T. and Mao, S. et al. 2013. Thermal plasma in the giant lobes of the radio galaxy Centaurus A. Astrophysical Journal. 764 (2).
    Source Title
    Astrophysical Journal
    DOI
    10.1088/0004-637X/764/2/162
    ISSN
    0004-637X
    School
    Curtin Institute of Radio Astronomy (Engineering)
    URI
    http://hdl.handle.net/20.500.11937/16431
    Collection
    • Curtin Research Publications
    Abstract

    We present a Faraday rotation measure (RM) study of the diffuse, polarized, radio emission from the giant lobes of the nearest radio galaxy, Centaurus A. After removal of the smooth Galactic foreground RM component, using an ensemble of background source RMs located outside the giant lobes, we are left with a residual RM signal associated with the giant lobes. We find that the most likely origin of this residual RM is from thermal material mixed throughout the relativistic lobe plasma. The alternative possibility of a thin-skin/boundary layer of magnetoionic material swept up by the expansion of the lobes is highly unlikely since it requires, at least, an order of magnitude enhancement of the swept-up gas over the expected intragroup density on these scales. Strong depolarization observed from 2.3 to 0.96 GHz also supports the presence of a significant amount of thermal gas within the lobes; although depolarization solely due to RM fluctuations in a foreground Faraday screen on scales smaller than the beam cannot be ruled out. Considering the internal Faraday rotation scenario, we find a thermal gas number density of ~10-4 cm -3, implying a total gas mass of ~1010 M ? within the lobes. The thermal pressure associated with this gas (with temperature kT ~ 0.5 keV, obtained from recent X-ray results) is approximately equal to the non-thermal pressure, indicating that over the volume of the lobes, there is approximate equipartition between the thermal gas, radio-emitting electrons, and magnetic field (and potentially any relativistic protons present). © 2013. The American Astronomical Society. All rights reserved.

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