Access to Astronomical Catalogues

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
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
    <ne><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:

       FileName      Lrecl  Records   Explanations

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


See also:
 J/ApJS/45/97 : Extragal. radio sources Faraday rotation (Simard-Normandin 1981)


Byte-by-byte Description of file: table2.dat

   Bytes Format Units   Label     Explanations

   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


Byte-by-byte Description of file: table3.dat

   Bytes Format Units   Label     Explanations

   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)

Note (1): Does not include the uncertainty due to ionospheric variations which
          are ≤1rad/m2.
Note (2): After correcting for the Galactic contribution.



Acknowledgements:
    Ilana Feain, ilana.feain(at)csiro.au
(End)                                        Patricia Vannier [CDS]  02-Nov-2009