J/ApJ/829/5 S-PASS & NVSS bright extragalactic radio sources (Lamee+, 2016)
Magnetic field disorder and Faraday effects on the polarization of
extragalactic radio sources.
Lamee M., Rudnick L., Farnes J.S., Carretti E., Gaensler B.M.,
Haverkorn M., Poppi S.
<Astrophys. J., 829, 5-5 (2016)>
=2016ApJ...829....5L 2016ApJ...829....5L (SIMBAD/NED BibCode)
ADC_Keywords: Polarization ; Radio sources ; Photometry, infrared
Keywords: catalogs; galaxies: evolution; galaxies: magnetic fields;
intergalactic medium; polarization; radio continuum: galaxies
Abstract:
We present a polarization catalog of 533 extragalactic radio sources
that have a 2.3GHz total intensity above 420mJy from the S-band
Polarization All Sky Survey, S-PASS, with corresponding 1.4GHz
polarization information from the NRAO VLA Sky Survey, NVSS. We
studied the selection effects and found that fractional polarization,
π, of radio objects at both wavelengths depends on the spectral
index, the source magnetic field disorder, the source size, and
depolarization. The relationship between depolarization, spectrum, and
size shows that depolarization occurs primarily in the source
vicinity. The median π2.3 of resolved objects in NVSS is
approximately two times larger than that of unresolved sources.
Sources with little depolarization are ∼2 times more polarized than
both highly depolarized and re-polarized sources. This indicates that
intrinsic magnetic field disorder is the dominant mechanism
responsible for the observed low fractional polarization of radio
sources at high frequencies. We predict that number counts from
polarization surveys will be similar at 1.4GHz and at 2.3GHz, for
fixed sensitivity, although ∼10% of all sources may currently be
missing because of strong depolarization. Objects with
π1.4~π2.3≥4% typically have simple Faraday structures, so
they are most useful for background samples. Almost half of
flat-spectrum (α≥-0.5) and ∼25% of steep-spectrum objects are
re-polarized. Steep-spectrum, depolarized sources show a weak negative
correlation of depolarization with redshift in the range 0<z<2.3.
Previous non-detections of redshift evolution are likely due the
inclusion of re-polarized sources as well.
Description:
The S-band Polarization All Sky Survey (S-PASS) is a project to map
the southern sky at decl. < -1.0° in total intensity and linear
polarization. The observations were conducted with the 64m Parkes
Radio Telescope, NSW Australia at 2.3GHz. A description of S-PASS is
given in Carretti+ (2013Natur.493...66C 2013Natur.493...66C) and Carretti
(2010ASPC..438..276C 2010ASPC..438..276C).
We cross-match the S-PASS data with the 1.4GHz NRAO VLA Sky Survey
(NVSS) catalog (Condon+, 1998, VIII/65) and generate a new independent
depolarization catalog of bright extragalactic radio sources.
We matched our catalog to the Wide-field Infrared Survey Explorer,
WISE, catalog, Wright+ (2010AJ....140.1868W 2010AJ....140.1868W), with a search radius of
five arcseconds. See section 4.7.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 326 533 Full catalog
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See also:
II/311 : WISE All-Sky Data Release (Cutri+ 2012)
VIII/65 : 1.4GHz NRAO VLA Sky Survey (NVSS) (Condon+ 1998)
J/ApJS/212/15 : Polarized NVSS sources SEDs (Farnes+, 2014)
J/ApJ/771/105 : MWA Stokes I 189MHz sources (Bernardi+, 2013)
J/MNRAS/436/2915 : Polarization of bright AT20G sources (Massardi+, 2013)
J/ApJ/755/21 : Extragalactic radio source rotation measures (Mao+, 2012)
J/AJ/144/105 : MOJAVE. VIII. Faraday rotation in AGN jets. (Hovatta+, 2012)
J/ApJS/188/178 : VLA 1.4GHz obs. of GOODS-North field (Morrison+, 2010)
J/MNRAS/402/2792 : 1388MHz ATLBS Low-Brightness Survey (Subrahmanyan+, 2010)
J/ApJ/702/1230 : Rotation measure image of the sky (Taylor+, 2009)
J/ApJ/666/201 : Radio polarimetry of the ELAIS N1 field (Taylor+, 2007)
J/MNRAS/371/898 : Extragalactic radio sources at 20GHz (Sadler+, 2006)
J/MNRAS/360/1305 : Polarization of extragalactic sources (Roy+, 2005)
J/ApJS/124/285 : VLA Images of Extragalactic Objects (Reid+, 1999)
J/A+AS/135/571 : Extragalactic radio sources polarization (Zukowski+, 1999)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 14 A14 --- NVSS NVSS name (JHHMMSS+DDMMSS) (1)
16- 24 F9.5 deg RAdeg NVSS Right Ascension (J2000) (1)
26- 34 F9.5 deg DEdeg NVSS Declination (J2000) (1)
36- 44 F9.5 deg GLON Galactic longitude (1)
46- 54 F9.5 deg GLAT Galactic latitude (1)
56- 62 F7.2 mJy INV [24/9718] NVSS target total intensity (2)
64- 69 F6.2 mJy e_INV [1/292] Uncertainty in INV
71- 76 F6.2 mJy PNV [0.1/291] NVSS target polarized intensity (2)
78- 81 F4.2 mJy e_PNV [0.2/0.6] Uncertainty in PNV
83- 88 F6.4 --- PiNV [0.001/0.16] NVSS fractional polarization (3)
90- 95 F6.4 --- e_PiNV [0.0001/0.02] Uncertainty in PiNV
97- 98 I2 --- f_PiNV Upper limit flag on PiNV: limit=-1; detection=1
100-107 F8.4 deg NVPA ? NVSS polarization angle (1)
109-114 F6.4 deg e_NVPA ? Uncertainty in NVPA (1)
116-121 F6.2 arcsec majaxis [14/127] NVSS fitted deconvolved major axis (1)
123-124 I2 --- f_majaxis Upper limit flag on majaxis: limit=-1;
resolved=1 (1)
126-131 F6.2 arcsec minaxis [13/100] NVSS fitted deconvolved minor axis (1)
133-134 I2 --- f_minaxis Upper limit flag on minaxis: limit=-1;
resolved=1 (1)
136-143 F8.2 mJy ISP [435/10096] S-PASS peak intensity
145-149 F5.2 mJy e_ISP [7/18] Uncertainty in ISP
151-156 F6.2 mJy PSP [-1.7/427] S-PASS polarized intensity
158-162 F5.2 mJy e_PSP [0.5/33] S-PASS Uncertainty in PSP
164-169 F6.4 --- PiSP [0.005/0.3] S-PASS fractional polarization (3)
171-176 F6.4 --- e_PiSP [0.0002/0.04] Uncertainty in PiSP
178-179 I2 --- f_PiSP Upper limit flag on PiSP: limit=-1; detection=1
181-188 F8.4 deg SPPA ? S-PASS polarization angle
190-195 F6.4 deg e_SPPA ? Uncertainty in SPPA
197-201 F5.2 --- alpha [-1.8/7.5] Spectral index derived from NVSS
and S-PASS
203-206 F4.2 --- e_alpha [0.04/0.07] Uncertainty in alpha
208-212 F5.2 --- Depol [0.09/34.2]? Depolarization (4)
214-217 F4.2 --- e_Depol [0/7.1]? Uncertainty in Depol
219-225 F7.2 rad/m2 RMT [-175/218]? Taylor+ 2009, J/ApJ/702/1230,
rotation measure
227-231 F5.2 rad/m2 e_RMT [0.3/18]? Uncertainty in RMT * 1.22
233-239 F7.2 rad/m2 RMNS [-167/164]? Rotation measure derived from NVSS
and S-PASS
241-244 F4.2 rad/m2 e_RMNS [0.09/7]? Uncertainty in RMNS
246-251 F6.2 rad/m2 DeltaRM [-55/55]? Rotation measure difference; RMNS-RMT
253-257 F5.2 rad/m2 e_DeltaRM [0.4/18]? Uncertainty in DeltaRM
259-265 F7.2 rad/m2 MedRMT [-125/92]? Median RMT (5)
267-268 I2 --- o_MedRMT [12/56]? Number of sources contributed
to MedRMT
270-275 F6.4 --- z [0.004/3.8]? Redshift from
Hammond+ 2012arXiv1209.1438H 2012arXiv1209.1438H
277-281 F5.2 mag W1mag [4/18]? WISE catalog W1 (3.4 micron) magnitude
283-286 F4.2 mag e_W1mag [0.02/0.3]? Uncertainty in W2mag
288-292 F5.2 --- n_W1mag [4/51]? W1 detection signal to noise ratio
294-298 F5.2 mag W2mag [3/17]? WISE catalog W2 (4.6 micron) magnitude
300-303 F4.2 mag e_W2mag [0.02/0.4]? Uncertainty in W2mag
305-309 F5.2 --- n_W2mag [1/56]? W2 detection signal to noise ratio
311-315 F5.2 mag W3mag [-0.6/13]? WISE catalog W3 (12um) magnitude
317-320 F4.2 mag e_W3mag [0.01/0.6]? Uncertainty in W2mag
322-326 F5.2 --- n_W3mag [-2/73]? W3 detection signal to noise ratio
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Note (1): These are directly extracted from the NVSS catalog.
Note (2): Plus the contribution from contaminating objects.
Note (3): In case of no detection the upper limit value is used.
Note (4): Defined as PiSP/PiNV. See f_PiSP or f_PiNV to determine whether
upper limits were used.
Note (5): Extracted from Taylor et al. (2009, J/ApJ/702/1230) RM
catalog with at least 30 0bjects contributing to the median value.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDSJ] 06-Dec-2016