Browse
this table...

AT20GBSPOL - Bright Extra-Galactic AT20G Sources Polarizations Catalog

HEASARC
Archive

Overview

This table contains polarization data for 180 extragalactic sources extracted from the Australia Telescope 20-GHz (AT20G) survey catalog and observed with the Australia Telescope Compact Array (ATCA) during a dedicated, high sensitivity run (sigmaP ~ 1 mJy). For the sake of completeness, the authors extracted the polarization information for seven extended sources from the 9-yr Wilkinson Microwave Anisotropy Probe co-added maps at 23 GHz. The full sample of 187 sources constitutes a ~ 99% complete sample of extragalactic sources brighter than S20GHz = 500 mJy at the selection epoch with Declination below -30o. The sample has a 91.4% detection rate in polarization at ~ 20 GHz (94% if considering the sub-sample of point-like sources). The authors have measurements also at 4.8 and 8.6 GHz within ~1 month of the 20-GHz observations for 172 sources so as to reconstruct the spectral properties of the sample in total intensity and in polarization: 143 of them have a polarization detection at all three frequencies.

The authors find that there is no statistically significant evidence of a relationship either between the fraction of polarization and frequency or between the fraction of polarization and the total intensity flux density. This indicates that Faraday depolarization is not very important above 4.8 GHz and that the magnetic field is not substantially more ordered in the regions dominating the emission at higher frequencies (up to 20 GHz). The authors estimate the distribution of the polarization fraction and the polarized flux density source counts at ~20 GHz.

The selection of the sample was based on the list of confirmed AT20G sources available at the epoch of these observations (2006 October). The authors selected all objects with flux density S20GHz > 500 mJy and Declination below -30o, excluding the Galactic plane region (|b| <= 1.5o^) and the Large Magellanic Cloud (LMC) region (inside a circle of 5.5o radius centered at RA =05:23:34.7 and Dec=-69:45:22 in J2000.0 coordinates). This resulted in a complete sample of 189 sources. The observations were taken on October 1, 2006 using the most compact hybrid configuration of ATCA, H75, excluding the data from the farthest antenna. The longest baseline of this configuration is 75 m, and its T-shape ensures adequate Fourier coverage for snapshots taken on a relatively small range of hour angles and at high elevation.

In a number of cases, indicated by source_flags values of 's', 'f' or 'w', the highest frequency data is not at 18 GHz, but at 20 or 23 GHz.


Catalog Bibcodes

2013ApJ...768...37C
2013MNRAS.434..956C
2010MNRAS.402.2403M

References

A polarization survey of bright extragalactic AT20G sources.
    Massardi M., Burke-Spolaor S.G., Murphy T., Ricci R., Lopez-Caniego M.,
    Negrello M., Chhetri R., De Zotti G., Ekers R.D., Partridge R.B.,
    Sadler E.M.
   <Mon. Not. R. Astron. Soc., 436, 2915-2928 (2013)>
   =2013MNRAS.436.2915M

The AT20G high-angular-resolution catalogue
    Chhetri R., Ekers R. D., Jones P. A., Ricci R.
   <Mon. Not. R. Astron. Soc., 434, 956-965 (2013)>
   =2013MNRAS.434..956C

The Australia Telescope 20GHz Survey (AT20G), Version XX October 2009.
    Murphy T., Sadler E.M., Ekers R.D., Massardi M., Hancock P.J., Mahony E.,
    Ricci R., Burke-Spolaor S., Calabretta M., Chhetri R., De Zotti G.,
    Edwards P.G., Ekers J.A., Jackson C.A., Kesteven M.J., Lindley E.,
    Newton-McGee K., Phillips C., Roberts P., Sault R.J., Staveley-Smith L.,
    Subrahmanyan R., Walker M.A., Wilson W.E.
   <Mon. Not. R. Astron. Soc. 402, 2403 (2010)>
   =2010MNRAS.402.2403M

Provenance

This table was created by the HEASARC in January 2015 based on the CDS Catalog J/MNRAS/436/2915 file table2.dat.

Parameters

Name
The radio source designation in the form recommended by the CDS Dictionary of Nomenclature of Celestial Objects for AT20G radio sources, e.g., 'AT20G JHHMMSS+DDMMSS', except for the source Fornax A.

RA
The Right Ascension of the radio source in the selected equinox. This was populated by the HEASARC from the position given in the AT20G table, except for the source Fornax A for which the HEASARC used the Simbad position.

Dec
The Declination of the radio source in the selected equinox. This was populated by the HEASARC from the position given in the AT20G table, except for the source Fornax A for which the HEASARC used the Simbad position.

LII
The Galactic Longitude of the radio source.

BII
The Galactic Latitude of the radio source.

Flux_18_GHz
The 18-GHz scalar average Stokes I flux density (intensity) of the radio source, in mJy.

Flux_18_GHz_Error
The uncertainty in the 18-GHz scalar average Stokes I flux density, in mJy, as given by equation (3) in the reference paper.

Pol_Flux_18_GHz_Limit
This parameter is set to '<' if the corresponding polarized flux density in this band is a 3-sigma upper limit rather than a detection.

Pol_Flux_18_GHz
The polarized flux density (intensity) P of the radio source at 18 GHz, in mJy, given by P = sqrt[Q2 + U2 - sigma(V)2], where Q, U and V are the usual Stokes parameters, and sigma(V) is the rms noise in the Stokes V image.

Pol_Flux_18_GHz_Error
The uncertainty in the 18-GHz polarized flux density (intensity), in mJy, of the radio source, calculated using equation (5) in the reference paper.

Frac_Pol_18_GHz
The fractional polarization (linear polarization degree) of the radio source at 18 GHz, P/I, in percent.

Frac_Pol_18_GHz_Error
The uncertainty in the fractional polarization of the radio source at 18 GHz, P/I, in percent, calculated using the usual error propagation from the uncertainties in the total and polarized flux densities at this frequency.

Pol_Angle_18_GHz
The polarization angle (phi) of the radio source at 18 GHz, given by the equation phi = (1/2) * arctan (U/Q), where Q and U are the usual Stokes parameters.

Flux_8p6_GHz
The 8.6-GHz total Stokes I flux density (intensity) of the radio source, in mJy.

Flux_8p6_GHz_Error
The uncertainty in the 8.6-GHz total Stokes I flux density (intensity) of the radio source, in mJy.

Pol_Flux_8p6_GHz_Limit
This parameter is set to '<' if the corresponding polarized flux density in this band is a 3-sigma upper limit rather than a detection.

Pol_Flux_8p6_GHz
The polarized flux density (intensity) P of the radio source at 8.6 GHz, in mJy, given by P = sqrt[Q2 + U2 - sigma(V)2], where Q, U and V are the usual Stokes parameters, and sigma(V) is the rms noise in the Stokes V image.

Pol_Flux_8p6_GHz_Error
The uncertainty in the 8.6-GHz polarized flux density (intensity), in mJy, of the radio source, calculated using equation (5) in the reference paper.

Frac_Pol_8p6_GHz
The fractional polarization (linear polarization degree) of the radio source at 8.6 GHz, P/I, in percent.

Frac_Pol_8p6_GHz_Error
The uncertainty in the fractional polarization of the radio source at 8.6 GHz, P/I, in percent, calculated using the usual error propagation from the uncertainties in the total and polarized flux densities at this frequency.

Pol_Angle_8p6_GHz
The polarization angle (phi) of the radio source at 8.6 GHz, given by the equation phi = (1/2) * arctan (U/Q), where Q and U are the usual Stokes parameters.

Flux_4p8_GHz
The 4.8-GHz total Stokes I flux density (intensity) of the radio source, in mJy.

Flux_4p8_GHz_Error
The uncertainty in the 4.8-GHz total Stokes I flux density (intensity) of the radio source, in mJy.

Pol_Flux_4p8_GHz_Limit
This parameter is set to '<' if the corresponding polarized flux density in this band is a 3-sigma upper limit rather than a detection.

Pol_Flux_4p8_GHz
The polarized flux density (intensity) P of the radio source at 4.8 GHz, in mJy, given by P = sqrt[Q2 + U2 - sigma(V)2], where Q, U and V are the usual Stokes parameters, and sigma(V) is the rms noise in the Stokes V image.

Pol_Flux_4p8_GHz_Error
The uncertainty in the 4.8-GHz polarized flux density (intensity), in mJy, of the radio source, calculated using equation (5) in the reference paper.

Frac_Pol_4p8_GHz
The fractional polarization (linear polarization degree) of the radio source at 4.8 GHz, P/I, in percent.

Frac_Pol_4p8_GHz_Error
The uncertainty in the fractional polarization of the radio source at 4.8 GHz, P/I, in percent, calculated using the usual error propagation from the uncertainties in the total and polarized flux densities at this frequency.

Pol_Angle_4p8_GHz
The polarization angle (phi) of the radio source at 4.8 GHz, given by the equation phi = (1/2) * arctan(U/Q), where Q and U are the usual Stokes parameters.

AT20G_Ls_Vis_Ratio
The ratio between the visibilities amplitude averaged over the long baselines (~ 4.5 km) and the visibilities amplitude averaged over the short baselines (~ 0.2 km) in the AT20G High Angular-Resolution Catalog (Chhetri et al. 2013, MNRAS, 434,956, available as the HEASARC as the AT20GHARC table).

Source_Flags
This parameter contains flag(s) indicating the presence of notes concerning the radio source, as follows:

   s = for sources with low declination observed during the AT20G 20-GHz run
        (i.e. the highest frequency is 20 GHz instead of 18 GHz);
   f = for sources with data at 20 GHz observed in March 2006 because of the
        poor quality of their data in the 2006 October runs;
   b = for very extended sources included in the Burke-Spolaor et al.
        (2009, MNRAS, 395, 504) sample;
   w = for extended sources which have had flux densities (or their upper limits)
        extracted from the WMAP 23-GHz 9-yr co-added maps (i.e. the highest
        frequency is 23 GHz instead of 18 GHz);
   c = for sources candidate to be suitable polarization calibrators at mm and
        sub-mm wavelengths.
  

Contact Person

Questions regarding the AT20GBSPOL database table can be addressed to the HEASARC User Hotline.

Page Author: Browse Software Development Team
Last Modified: 20-Jan-2015