FARADAY ROTATION STRUCTURE ON KILOPARSEC SCALES IN THE RADIO LOBES OF CENTAURUS A
- CSIRO Australia Telescope National Facility, P.O. Box 76, Epping, NSW 1710 (Australia)
- Sydney Institute for Astronomy, School of Physics, The University of Sydney, NSW 2006 (Australia)
- Curtin Institute of Radio Astronomy, Curtin University of Technology, GPO Box U1987, WA 6845 (Australia)
- School of Chemical and Physical Sciences, Victoria University of Wellington, PO Box 600, Wellington (New Zealand)
- National Radio Astronomical Observatory, P.O. Box O, 1003 Lopezville Road, Socorro, NM 87801-0387 (United States)
- Astronomisches Institut der Universitaet Bochum, Universitaetsstr. 150, 44801 Bochum (Germany)
We present the results of an Australia Telescope Compact Array 1.4 GHz spectropolarimetric aperture synthesis survey of 34 deg{sup 2} centered on Centaurus A-NGC 5128. A catalog of 1005 extragalactic compact radio sources in the field to a continuum flux density of 3 mJy beam{sup -1} is provided along with a table of Faraday rotation measures (RMs) and linear polarized intensities for the 28% of sources with high signal to noise in linear polarization. We use the ensemble of 281 background polarized sources as line-of-sight probes of the structure of the giant radio lobes of Centaurus A. This is the first time such a method has been applied to radio galaxy lobes and we explain how it differs from the conventional methods that are often complicated by depth and beam depolarization effects. Assuming a magnetic field strength in the lobes of 1.3 B {sub 1} muG, where B {sub 1} = 1 is implied by equipartition between magnetic fields and relativistic particles, the upper limit we derive on the maximum possible difference between the average RM of 121 sources behind Centaurus A and the average RM of the 160 sources along sightlines outside Centaurus A implies an upper limit on the volume-averaged thermal plasma density in the giant radio lobes of (n{sub e} ) < 5 x 10{sup -5} B {sup -1} {sub 1} cm{sup -3}. We use an RM structure function analysis and report the detection of a turbulent RM signal, with rms sigma{sub RM} = 17 rad m{sup -2} and scale size 0.{sup 0}3, associated with the southern giant lobe. We cannot verify whether this signal arises from turbulent structure throughout the lobe or only in a thin skin (or sheath) around the edge, although we favor the latter. The RM signal is modeled as possibly arising from a thin skin with a thermal plasma density equivalent to the Centaurus intragroup medium density and a coherent magnetic field that reverses its sign on a spatial scale of 20 kpc. For a thermal density of n {sub 1} 10{sup -3} cm{sup -3}, the skin magnetic field strength is 0.8 n {sup -1} {sub 1} muG.
- OSTI ID:
- 21389327
- Journal Information:
- Astrophysical Journal, Vol. 707, Issue 1; Other Information: DOI: 10.1088/0004-637X/707/1/114; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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