J/ApJ/707/114 Faraday rotation in Cen A (Feain, 2009)
Faraday rotation structure on kiloparsec scales in the radio lobes of
Centaurus A.
Feain I.J., Ekers R.D., Murphy T., Gaensler B.M., Macquart J.-P.,
Norris R.P., Cornwell T.J., Johnston-Hollitt M., Ott J., Middelberg E.
<Astrophys. J. 707, 114 (2009)>
=2009ApJ...707..114F 2009ApJ...707..114F
ADC_Keywords: Galaxies, radio ; Radio sources ; Polarization ; Morphology
Keywords: galaxies: individual (Centaurus A, NGC 5128) -
techniques: interferometric - techniques: polarimetric
Abstract:
We present the results of an Australia Telescope Compact Array 1.4GHz
spectropolarimetric aperture synthesis survey of 34deg2 centered on
Centaurus A-NGC 5128. A catalog of 1005 extragalactic compact radio
sources in the field to a continuum flux density of 3mJy/beam 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 1.3B1uG, where B1=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
<5x10-5B1-1cm-3. We use an RM structure function analysis
and report the detection of a turbulent RM signal, with rms=17rad/m2
and scale size 0.3deg, 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 20kpc. For
a thermal density of n1 10-3cm-3, the skin magnetic field strength
is 0.8n1-1uG.
Description:
Positions, sizes and 1.4GHz flux densities for 1005 compact radio
sources in a 34deg2 field centred on Centaurus A to a flux density
of 3mJy/beam. Also, polarisation and Faraday rotation for the
281/1005 sources with a high signal to noise (S/N>7) in linear
polarised intensity.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 99 1005 Radio continuum properties of 1005 sources to
3mJy/beam
table3.dat 68 281 Polarisation properties of 281 sources
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See also:
J/ApJS/45/97 : Extragal. radio sources Faraday rotation (Simard-Normandin 1981)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 13 A13 --- Name Source Name (HHMMSS-DDMMSS)
16- 17 I2 h RAh Hour of Right Asecension (J2000)
19- 20 I2 min RAm Minute of Right Asecension (J2000)
22- 26 F5.2 s RAs Second of Right Asecension (J2000)
29 A1 --- DE- Sign of the Declination (J2000)
30- 31 I2 deg DEd Degree of Declination (J2000)
33- 34 I2 arcmin DEm Arcminute of Declination (J2000)
36- 39 F4.1 arcsec DEs Arcsecond of Declination (J2000)
42- 46 F5.1 mJy pFlux Peak 1.4GHz flux density (mJy/beam)
48- 51 F4.1 mJy e_pFlux Error in pFlux
54- 58 F5.1 mJy iFlux Integrated 1.4GHz flux density (mJy)
60- 63 F4.1 mJy e_iFlux Error in iFlux
65- 69 F5.1 arcsec fMaj Fitted major axis
72- 75 F4.1 arcsec fMin Fitted minor axis
77- 81 F5.1 deg fPA Fitted position angle
84- 87 F4.1 arcsec dMaj ? Deconvolved major axis
90- 93 F4.1 arcsec dMin ? Deconvolved minor axis
95- 99 F5.1 deg dPA ? Deconvolved position angle
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 13 A13 --- Name Source Name (HHMMSS-DDMMSS)
15- 16 I2 h RAh Hour of Right Asecension (J2000)
18- 19 I2 min RAm Minute of Right Asecension (J2000)
21- 25 F5.2 s RAs Second of Right Asecension (J2000)
27 A1 --- DE- Sign of the Declination (J2000)
28- 29 I2 deg DEd Degree of Declination (J2000)
31- 32 I2 arcmin DEm Arcminute of Declination (J2000)
34- 38 F5.2 arcsec DEs Arcsecond of Declination (J2000)
40- 44 F5.2 mJy pFlux Peak polarised 1.4GHz flux density (mJy/beam)
46- 50 F5.1 --- SNR Signal-to-Noise in pFLux
52- 57 F6.1 rad/m2 RM Measured Faraday rotation measure
59- 62 F4.1 rad/m2 e_RM Uncertainty in RM (1)
64- 68 F5.1 rad/m2 RMcor Faraday rotation measure (2)
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Note (1): Does not include the uncertainty due to ionospheric variations which
are ≤1rad/m2.
Note (2): After correcting for the Galactic contribution.
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Acknowledgements:
Ilana Feain, ilana.feain(at)csiro.au
(End) Patricia Vannier [CDS] 02-Nov-2009