J/A+A/555/A4 Radio polarimetry of CSS sources (Mantovani+ 2013)
Radio polarimetry of compact steep spectrum sources at sub-arcsecond resolution.
Mantovani F., Rossetti A., Junor W., Saikia D.J., Salter C.J.
<Astron. Astrophys. 555, A4 (2013)>
=2013A&A...555A...4M 2013A&A...555A...4M
ADC_Keywords: Galaxies, radio ; QSOs ; Polarization ; Interferometry
Keywords: polarisation - quasars: general - galaxies: jets -
radio continuum: galaxies
Abstract:
We present multi-frequency VLA polarisation observations of compact
steep spectrum (CSS) sources. About half of the sources are point-like
even at the resolution of about 0.1x0.1 arcseconds. The remaining
sources have double or triple structure. Low values for the percentage
of polarised emission in CSS sources is confirmed. On the average,
quasars are more polarised than galaxies. A wide range of RM values
have been measured. There are clear indications of very large RMs up
to about 5585rad/m2. CSS galaxies are characterized by RM values
that are larger than CSS quasars. The majority of the objects show
very large values of RM.
Description:
Polarimetric observations of our sample of 29 compact steep spectrum
(CSS) sources were made at 8, 15 and 23GHz on August 6th, 1991 using
the VLA in A-array. The observations were scheduled in "bracket" mode,
i.e. calibrator-source-calibrator, to obtain the best possible phase
correction. The data were recorded in both circular polarisations, and
calibrated in the standard way using AIPS procedures. The sources
2200+420 (BLLac) and 0923+392 were observed regularly throughout the
observing period to allow for parallactic angle corrections.
Calibration of the Electric Vector Position Angle (EVPA) was performed
by observing the source 1328+307 (3C286) assuming an EVPA of 33°
for it at all frequencies. An iterative procedure was carried out
using the IMAGR and CALIB programmes to self-calibrate the
parallel-hand (LL or RR) fringes. The complex gain corrections derived
in this way were also applied to the cross-hand (RL or LR) fringes.
Images in Stokes parameters I, Q, and U were produced. Images of the
polarised flux density P=(Q2+U2)0.5 and EVPA,
chi=0.5xtan-1(U/Q), were then generated from the Q and U images. The
data acquired with the 8GHz receiver were separately imaged for the
two IFs, namely IF1 at 8085MHz and IF2 at 8485MHz, each having a
bandwidth of 50MHz.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 20 4 Percentage polarizations for the whole sample
and for galaxies and quasars separately
table2.dat 65 29 Integrated polarisation percentages for each source
table3.dat 84 53 Polarisation parameters for components of each
source at 8085MHz
table4.dat 84 53 Polarisation parameters for components of each
source at 8485MHz
table5.dat 84 60 Polarisation parameters for components of each
source at 14885MHz
table6.dat 84 32 Polarisation parameters for components of each
source at 23285MHz
table7.dat 75 57 Fractional polarisation, depolarisation index and
rotation measure for individual components
of each source
list.dat 81 4 List of total intensity, Stokes Q and Stokes U fits
images of four sources at 14885MHz (see figure 1)
fits/* . 12 Individual fits images
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See also:
J/A+A/369/380 : CSS/GPS radio sources VLA observations (Fanti+, 2001)
J/A+A/402/171 : Faint CSS radio sources at 74 MHz (Tschager+, 2003)
J/A+A/426/463 : B3-VLA CSS sample (Orienti+, 2004)
J/MNRAS/416/1135 : Unbiased sample of CSS and GPS (Randall+, 2011)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 5 I5 MHz Freq [8085/23285] Observing frequency
7 A1 --- u_all [~] Uncertainty flag on all
8- 10 F3.1 % all Percentage polarization (<mtot>) for the
whole sample
12 A1 --- u_G [~] Uncertainty flag on G
13- 15 F3.1 % G Percentage polarization (<mtot>) for galaxies
17 A1 --- u_Q [~] Uncertainty flag on Q
18- 20 F3.1 % Q Percentage polarization (<mtot>) for quasars
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 9 A9 --- Name Source name
11- 17 A7 --- OName Other name
19 A1 --- T [G/Q] Optical type: Galaxy or Quasar
21- 26 F6.4 --- z ? Redshift
28- 29 A2 --- RS Radio structure
31- 34 F4.2 % m8.0 ? Polarisation percentage at 8085MHz
36- 39 F4.2 % m8.4 ? Polarisation percentage at 8485MHz
41- 44 F4.2 % m14.8 ? Polarisation percentage at 18885MHz
46- 49 F4.2 % m23.2 ? Polarisation percentage at 23285MHz
51- 54 F4.2 --- DP8/8.4 ? Depolarisation index, DP, between 8485
and 8085MHz
56- 60 F5.3 --- DP8.4/14 ? Depolarisation index, DP, between 14885
and 8485MHz
62- 65 F4.2 --- DP14/23 ? Depolarisation index, DP, between 23285
and 14885MHz
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Byte-by-byte Description of file: table[3456].dat
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Bytes Format Units Label Explanations
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1- 9 A9 --- Name Source name
11- 17 A7 --- OName Other name
19 A1 --- T [GQE] Optical type: Galaxy, Quasar or Empty
21- 24 A4 --- Comp Component
26- 32 F7.2 mJy S ? Integrated component flux density (1)
33 A1 --- u_S [? ] Uncertainty flag on S
35- 38 F4.2 mJy 3sig ? 3σ noise in total-intensity image
in mJy/beam
40- 44 F5.2 mJy Sp ? Polarised flux density (1)
46- 49 F4.1 mJy Sp2 ? Second region polarised flux density
51- 53 F3.1 mJy Sp3 ? Third region polarised flux density
55- 58 F4.2 mJy 3sigp ? 3σ noise in the polarised-intensity
density in mJy/beam
60- 62 I3 deg EVPA [-90/90]? Electric vector position angle
63 A1 --- f_EVPA [a] a: Value in range 50-80
64- 66 I3 deg EVPA2 [-90/90]? Electric vector position angle of
second region (2)
68 I1 deg EVPA3 [-90/90]? Electric vector position angle of
third region (2)
70- 74 F5.3 arcsec amaj ? Deconvolved major axis of the components
76- 80 F5.3 arcsec bmin ? Deconvolved minor axis of the components
82- 84 I3 deg PA ? Deconvolved position angle of the components
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Note (1): At the observed frequency (8085MHz in table3, 8485MHz in table4,
14885MHz in table5 and 23285MHz in table6)
Note (2): When more than one EVPA is listed, these refer to regions with
different EVPAs.
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Byte-by-byte Description of file: table7.dat
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Bytes Format Units Label Explanations
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1- 9 A9 --- Name Source name
11- 17 A7 --- OName Other name
19 A1 --- T [GQE] Optical type: Galaxy, Quasar or Empty
21- 23 A3 --- Comp Source component
25- 29 F5.2 % m8.0 ? Polarisation percentage at 8085MHz
31- 35 F5.2 % m8.4 ? Polarisation percentage at 8485MHz
37- 41 F5.2 % m14.8 ? Polarisation percentage at 18885MHz
43- 47 F5.2 % m23.2 ? Polarisation percentage at 23285MHz
49- 52 F4.2 --- DP8/8.4 ? Depolarisation index, DP, between 8485 and
8085MHz
54- 57 F4.2 --- DP8.4/14 ? Depolarisation index, DP, between 14885
and 8485MHz
59- 62 F4.2 --- DP14/23 ? Depolarisation index, DP, between 23285
and 14885MHz
64- 68 I5 rad/m2 RM ? Rotation Measure
70- 75 I6 rad/m2 RM0 ? Rotation Measure in the source rest frame
RM(rf)=RM(1+z)2
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Byte-by-byte Description of file: list.dat
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Bytes Format Units Label Explanations
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1- 9 A9 --- Name Source name
11- 19 F9.5 deg RAdeg Right Ascension of center (J2000)
20- 28 F9.5 deg DEdeg Declination of center (J2000)
30- 34 F5.3 arcsec/pix Scale [0.025] Scale of the image
36- 38 I3 pix Nx [512] Number of pixels along X-axis
39 A1 --- --- [x]
40- 42 I3 pix Ny [512] Number of pixels along Y-axis
44- 48 I5 MHz Freq [14885] Frequency
50- 59 A10 --- FileNI Name of FITS "Total intensity image" file
in subdirectory fits
61- 70 A10 --- FileNQ Name of FITS "Stokes Q image" file
in subdirectory fits
72- 81 A10 --- FileNU Name of FITS "Stokes U image" file
in subdirectory fits
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Acknowledgements:
Franco Mantovani, fmantovani(at)ira.inaf.it
(End) Franco Mantovani [IRA-INAF], Emmanuelle Perret [CDS] 03-Jun-2013