J/ApJ/815/49 Spectropolarimetric survey of radio sources (Anderson+, 2015)
Broadband radio polarimetry and Faraday rotation of 563 extragalactic radio
sources.
Anderson C.S., Gaensler B.M., Feain I.J., Franzen T.M.O.
<Astrophys. J., 815, 49 (2015)>
=2015ApJ...815...49A 2015ApJ...815...49A (SIMBAD/NED BibCode)
ADC_Keywords: Radio sources ; Magnetic fields ; Redshifts ; Surveys
Keywords: galaxies: active - ISM: magnetic fields - magnetic fields -
radio continuum: galaxies - techniques: polarimetric
Abstract:
We present a broadband spectropolarimetric survey of 563 discrete,
mostly unresolved radio sources between 1.3 and 2.0 GHz using data
taken with the Australia Telescope Compact Array. We have used
rotation-measure synthesis to identify Faraday-complex polarized
sources, those objects whose frequency-dependent polarization behavior
indicates the presence of material possessing complicated magnetoionic
structure along the line of sight (LOS). For sources classified as
Faraday-complex, we have analyzed a number of their radio and
multiwavelength properties to determine whether they differ from
Faraday-simple polarized sources (sources for which LOS magnetoionic
structures are comparatively simple) in these properties. We use this
information to constrain the physical nature of the magnetoionic
structures responsible for generating the observed complexity. We
detect Faraday complexity in 12% of polarized sources at ∼1' resolution,
but we demonstrate that underlying signal-to-noise limitations mean
the true percentage is likely to be significantly higher in the
polarized radio source population. We find that the properties of
Faraday-complex objects are diverse, but that complexity is most often
associated with depolarization of extended radio sources possessing a
relatively steep total intensity spectrum. We find an association
between Faraday complexity and LOS structure in the Galactic
interstellar medium (ISM) and claim that a significant proportion of
the Faraday complexity we observe may be generated at interfaces of
the ISM associated with ionization fronts near neutral hydrogen
structures. Galaxy cluster environments and internally generated
Faraday complexity provide possible alternative explanations in some
cases.
Description:
We obtained mosaicked observations of a 30 deg2 region of sky using
the CABB correlator on the Australia Telescope Compact Array (ATCA;
Wilson et al. 2011MNRAS.416..832W 2011MNRAS.416..832W). Our observations were performed
using the "CFB 1M" mode, which generates all polarization products
from 1.1 to 3.1 GHz with 1 MHz channel widths. The mosaic consisted of
342 pointings laid out in a hexagonal grid. This grid spanned 7.5°
in RA and 5.5° in DE and was centered on RA=03h29m40s and
DE=-36°16'30" (J2000) in Fornax. The angular separation of the
mosaic pointings was 0.323° and therefore spatially Nyquist-sampled
at 1.4 GHz. To obtain adequate uv coverage, we broke the full mosaic
up into seven submosaics and observed each submosaic on consecutive
days. We completed the full seven-day observing run twice-once in
each of the 1.5B and 750B array configurations, from 2011 May 5-11
and 2011 June 10-16, respectively.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 161 160 Selected Quantities Calculated or Determined for
Polarized Sources in Our Sample.
(from erratum ApJ, 820, 144)
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See also:
VII/6 : Polarization of Extragalactic Radio Sources
(Eichendorf+ 1980)
J/MNRAS/190/205 : Magnetic fields in extragalactic radio sources
(Clarke+ 1980)
J/ApJS/45/97 : Extragal. Radio Sources Faraday Rotation
(Simard-Normandin+, 1981)
J/ApJ/586/826 : Chandra X-ray observations of NGC 1316 (Kim+, 2003)
J/MNRAS/362/9 : Radio-loud AGN in SDSS (Best+, 2005)
J/ApJ/663/258 : Rotation measures of extragalactic sources in SGPS
(Brown+, 2007)
J/ApJ/702/1230 : Rotation measure image of the sky (Taylor+, 2009)
J/AJ/144/105 : MOJAVE. VIII. Faraday rotation in AGN jets. (Hovatta+, 2012)
J/MNRAS/469/4034 : Broadband polarisation of radio AGN (O'Sullivan+, 2017)
Byte-by-byte Description of file: table1.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 Ascension (J2000)
18- 19 I2 min RAm Minute of Right Ascension (J2000)
21- 25 F5.2 s RAs Second of Right Ascension (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 F5.3 deg Sep Angular separation from the position of
the source nearest mosaic pointing
center
46- 51 F6.1 deg PA [] Position angle from the position of
the source nearest mosaic pointing
center
53 A1 --- Res [ru] Resolved (r) or unresolved (u)
source at the 90"x45" resolution of
spectropolarimetric images
55- 59 F5.3 m lambda0 Reference wavelength to 3 significant
figures
61- 66 F6.4 Jy Ilambda0 Interpolated value of Stokes I at
λ0
68- 73 F6.4 Jy e_Ilambda0 Uncertainty in Ilambda0
75- 79 F5.2 --- alphal0 Value of α evaluated at λ0
(1)
81- 84 F4.2 --- e_alphal0 Uncertainty in alphal0
86 A1 --- Cat [cs] Complexity categorization of the
source (2)
88- 89 I2 --- GES [6/10]? The highest RMCLEAN cutoff
Gaussian-equivalent significance (GES)
level at which the source appears
complex, in equivalent Gaussian σ
91 A1 --- Weight [cn-] The weighting scheme under which a
complex source attains its highest value
of σΦ (3)
93- 98 F6.2 rad/m2 sigmaPhi Calculated value of the dispersion of the
RMCLEAN model components, σΦ
100-104 F5.3 rad/m2/beam pcut The RMCLEAN cutoff value to 3 significant
figures
106-112 F7.5 rad/m2/beam p Amplitude of the Faraday Dispersion
Spectrum (FDS) at Φpeak
114-119 E6.1 rad/m2/beam e_p Uncertainty in p
121-124 F4.2 rad/m2/beam poff The fractional contribution of off-peak
RMCLEAN components to the total
polarized flux (4)
126-131 F6.1 rad/m2 Phipeak Faraday depth at which the FDS is maximum
133-135 F3.1 rad/m2 e_Phipeak Uncertainty in Phipeak
137-139 A3 --- Morph Stokes I morphology of the radio source
at 15" resolution (5)
141-143 A3 --- IRc [yes-no off] Counterpart status of a
source in IR (6)
145-147 A3 --- Oc [yes-no off] Counterpart status of a
source in optical (6)
149-151 A3 --- UVc [yes-no off] Counterpart status of a
source in UV (6)
153-155 A3 --- Xc [yes-no ] Counterpart status of a source
in X-rays (7)
157-161 F5.3 --- z ? Cross-matched redshift
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Note (1): Spectral index α (I(ν)∝να)
Note (2): Categorization as follows:
c = Faraday-complex source;
s = Simple source.
Note (3): Weighting scheme as follows:
c = Constant rotation measure (RM) synthesis weighting scheme;
n = Natural RM synthesis weighting scheme.
Note (4): Those RMCLEAN components found in Φ bins apart from that in which
the majority of components were found.
Note (5): Morphology as follows:
cj = "core-jet" if the total flux was dominated by an unresolved component in
the presence of additional resolved components that were either
(1) substantially fainter than the core or (2) radiated away from the
core with linear morphology;
lc = "lobe/jet component" if they either (1) possessed obvious radio lobe or
jet morphology or (2) possessed a counterpart radio source within 3' of
similar brightness (Hammond et al. 2012arXiv1209.1438H 2012arXiv1209.1438H and refs
therein);
u = "unresolved" if the source was well fit by a Gaussian of the same
dimensions as the restoring beam;
ext = "extended" for resolved sources not meeting the above criteria.
Note (6): In IR, optical, and UV, we manually identified counterparts by
overlaying contours from the source-finding image onto the relevant
survey images.
Counterpart status as follows:
yes = "match" when objects were present within 15" of the radio contour
centroid (i.e., within the beam FWHM of the source-finding image);
off = "match-off source" if either (1) the radio source was extended and a
candidate counterpart source lay inside the 10% radio flux contour,
(2) a second radio source was located within 3' and a candidate
counterpart was located within 15" of the position of the flux centroid
of the two sources (e.g., Best et al. 2005, J/MNRAS/362/9), or (3) NASA
Extragalactic Database (NED) queries revealed an existing association
in the literature;
no = "no match" otherwise.
Note (7): Our X-ray cross matches were made in a binary manner based on the
distance to the nearest cataloged sources and the positional errors
for the RASS-BSC and RASS-FSC (Parejko et al. 2008AJ....135...10P 2008AJ....135...10P).
Counterpart status as follows:
yes = "match" if the radio emission centroid fell within 20" of a cataloged
RASS-BSC source position or 40" of a RASS-FSC source position;
no = "no match" otherwise.
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History:
From electronic version of the journal
(End) Prepared by Tiphaine Pouvreau [CDS] 17-Oct-2017