J/MNRAS/436/2915 Polarization of bright AT20G sources (Massardi+, 2013)
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 2013MNRAS.436.2915M
ADC_Keywords: Galaxies, radio ; Polarization
Keywords: polarization; techniques: polarimetric - surveys - galaxies: active -
radio continuum: galaxies
Abstract:
We present polarization data for 180 extragalactic sources extracted
from the Australia Telescope 20GHz (AT20G) survey catalogue and
observed with the Australia Telescope Compact Array during a
dedicated, high sensitivity run (σP∼1mJy). For the sake
of completeness, we extracted the polarization information for seven
extended sources from the 9yr Wilkinson Microwave Anisotropy
Probe co-added maps at 23GHz. The full sample of 187 sources
constitutes a ≃99% complete sample of extragalactic sources
brighter than S20GHz=500mJy at the selection epoch with
declination δ←30°. The sample has a 91.4% detection rate in
polarization at ∼20GHz (94 percent if considering the subsample of
point-like sources). We have measurements also at 4.8 and 8.6GHz
within ∼1 month of the 20GHz observations for 172 sources 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.
We 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 4.8GHz and that the magnetic field is not
substantially more ordered in the regions dominating the emission at
higher frequencies (up to 20GHz). We estimate the distribution of the
polarization fraction and the polarized flux density source counts at
∼20GHz.
Description:
The selection of the sample was based on the list of confirmed AT20G
sources available at the epoch of our observations (2006 October). We
selected all objects with flux density S20GHz>500mJy and
declination DE←30°, excluding the Galactic plane region
(|b|≤1.5°) and the Large Magellanic Cloud (LMC) region (inside a
circle of 5.5° radius centred at RA=05:23:34.7 and DE=-69:45:22).
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 75m,
and its T-shape ensures adequate Fourier coverage for snapshots taken
on a relatively small range of hour angles and at high elevation.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 155 187 Catalogue of the sources of the extragalactic
sample observed in the AT20G run dedicated to
high sensitivity polarization
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See also:
J/MNRAS/402/2403 : Australia Telescope 20GHz Survey Catalog (Murphy+, 2010)
J/MNRAS/417/2651 : AT20G-optical catalogue (Mahony+, 2011)
J/MNRAS/434/956 : AT20G high-angular-resolution catalogue (Chhetri+, 2013)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 5 A5 --- --- [AT20G]
6- 19 A14 --- AT20G AT20G name (JHHMMSS+DDMMSS), or Fornax A
21- 27 F7.1 mJy S(18) 18GHz scalar average flux density
29- 33 F5.1 mJy e_S(18) rms uncertainty on S(18G)
35 A1 --- l_P(18) [<] Limit flag on P(18G)
36- 42 F7.2 mJy P(18) Polarised flux density at 18GHz
44- 47 F4.1 mJy e_P(18) ?=- rms uncertainty on P(18G)
49- 53 F5.2 % m(18) ?=- Fractional polarisation at 18GHz
55- 58 F4.2 % e_m(18) ?=- rms uncertainty on m(18G)
60- 65 F6.2 deg PA(18) [-90/90]?=- Polarisation angle at 18GHz
67- 73 F7.1 mJy S(8.6) ?=- Total intensity flux density at 8.6GHz
75- 77 F3.1 mJy e_S(8.6) ?=- rms uncertainty on S(8.6)
79 A1 --- l_P(8.6) [<] Limit flag on P(8.6)
80- 85 F6.2 mJy P(8.6) ?=- Polarised flux density at 8.6GHz
87- 89 F3.1 mJy e_P(8.6) ?=- rms uncertainty on P(8.6)
91- 94 F4.2 % m(8.6) ?=- Polarisation degree at 8.6GHz
96- 99 F4.2 % e_m(8.6) ?=- rms uncertainty on m(8.6)
101-106 F6.2 deg PA(8.6) [-90/90]?=- Polarisation angle at 8.6GHz
108-113 F6.1 mJy S(4.8) ?=- Total intensity flux density at 4.8GHz
115-117 F3.1 mJy e_S(4.8) ?=- rms uncertainty on S(4.8)
119 A1 --- l_P(4.8) [<] Limit flag on P(4.8)
120-125 F6.2 mJy P(4.8) ?=- Polarised flux density at 4.8GHz
127-129 F3.1 mJy e_P(4.8) ?=- rms uncertainty on P(4.8)
131-134 F4.2 % m(4.8) ?=- Polarisation degree at 4.8GHz
136-139 F4.2 % e_m(4.8) ?=- rms uncertainty on m(4.8)
141-146 F6.2 deg PA(4.8) [-90/90]?=- Polarisation angle at 4.8GHz
148-151 F4.2 --- 6kmVis ?=- Ratio between the visibilities amplitudes (2)
153-155 A3 --- f_AT20G Flags on source (1)
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Note (1): Flags as follows:
s = for sources with low declination observed during the AT20G 20GHz run
(i.e. the highest frequency is 20GHz instead of 18GHz)
f = for sources with data at 20GHz 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) sample
w = for extended sources which have had flux densities (or their upper limits)
extracted from the WMAP 23GHz 9-yr coadded maps (i.e. the highest
frequency is 23GHz instead of 18GHz)
c = for sources candidate to be suitable polarisation calibrators at mm and
submm wavelengths
Note (2): Ratio between the visibilities amplitude averaged over the long
baselines and the short ones in the AT20G catalogue
(Chhetri et al., 2013MNRAS.434..956C 2013MNRAS.434..956C, Cat. J/MNRAS/434/956)
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 23-Oct-2014