J/ApJ/714/1170 Faraday rotation at high Galactic latitude (Mao+, 2010)
A survey of extragalactic Faraday rotation at high Galactic latitude:
the vertical magnetic field of the Milky Way toward the Galactic poles.
Mao S.A., Gaensler B.M., Haverkorn M., Zweibel E.G., Madsen G.J.,
McClure-Griffiths N.M., Shukurov A., Kronberg P.P.
<Astrophys. J., 714, 1170-1186 (2010)>
=2010ApJ...714.1170M 2010ApJ...714.1170M
ADC_Keywords: Milky Way ; Magnetic fields ; Radio sources ; Polarization ;
Galaxies, rotation
Keywords: Galaxy: halo - ISM: magnetic fields - polarization
Abstract:
We present a study of the vertical magnetic field of the Milky Way
toward the Galactic poles, determined from observations of Faraday
rotation toward more than 1000 polarized extragalactic radio sources
at Galactic latitudes |b|≥77°, using the Westerbork Radio
Synthesis Telescope and the Australia Telescope Compact Array. We find
median rotation measures (RMs) of 0.0±0.5rad/m2 and
+6.3±0.7rad/m2 toward the north and south Galactic poles,
respectively, demonstrating that there is no coherent vertical
magnetic field in the Milky Way at the Sun's position. If this is a
global property of the Milky Way's magnetism, then the lack of
symmetry across the disk rules out pure dipole or quadrupole
geometries for the Galactic magnetic field. The angular fluctuations
in RM seen in our data show no preferred scale within the range
∼0.1° to ∼25°. The observed standard deviation in RM of
∼9rad/m2 then implies an upper limit of ∼1uG on the strength of the
random magnetic field in the warm ionized medium at high Galactic
latitudes.
Description:
We applied appropriate filters to the NVSS catalog (Condon et al.
1998, Cat. VIII/65) to yield a target list consisting of highly
polarized compact extragalactic radio sources (EGSs) near the Galactic
poles, toward which one can measure RMs (Faraday rotation measures).
RMs of EGSs toward the north Galactic pole were acquired at the
Westerbork Synthesis Radio Telescope (WSRT) over the period 2006 July
23rd to August 20th using the 9A=96m array configuration spanning
baselines from 96m to 2760m; with eight 20MHz frequency bands (each
band is composed of 64 channels of width 0.3125MHz) centered on each
of 1381MHz and 1713MHz. Additional observations were made on 2009
April 7-8 with the mini-short configuration, spanning baselines from
96m to 2723m centered on only 1381MHz.
RMs of EGSs toward the south Galactic pole were acquired at the
Australia Telescope Compact Array (ATCA) over the period 2006 June
23rd to July 4th, using the 1.5-dimensional array configuration
spanning baselines from 107.1m to 1439m (without antenna 6), and
2008 June 22nd and June 25th, using the EW352 array configuration
spanning baselines from 30.6m to 352m (without antenna 6). All ATCA
data consist of 32 adjacent frequency channels each of bandwidth 4MHz
centered on each of 1384MHz and 2368MHz.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 68 472 Rotation measures of extragalactic sources
towards the north Galactic pole, sorted by
Galactic longitude
table2.dat 68 341 Rotation measures of extragalactic sources
towards the south Galactic pole, sorted by
Galactic longitude
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See also:
VIII/65 : 1.4GHz NRAO VLA Sky Survey (NVSS) (Condon+ 1998)
J/A+A/513/A65 : Rotation measures in the fourth Galactic quadrant (Nota+,
2010)
J/ApJ/702/1230 : Rotation measure image of the sky (Taylor+, 2009)
J/MNRAS/386/1881 : New pulsar rotation measures (Noutsos+, 2008)
J/ApJ/663/258 : Rotation measures of extragalactic sources in SGPS (Brown+,
2007)
J/ApJ/642/868 : Rotation measures for 223 pulsars (Han+, 2006)
J/ApJS/145/213 : Rotation measures of compact sources in CGPS (Brown+, 2003)
J/A+A/372/276 : Polarization catalogue for NGP area (Berdyugin+, 2001)
Byte-by-byte Description of file: table[12].dat
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Bytes Format Units Label Explanations
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1- 2 I2 h RAh Hour of Right Ascension (J2000)
4- 5 I2 min RAm Minute of Right Ascension (J2000)
7- 11 F5.2 s RAs Second of Right Ascension (J2000)
13 A1 --- DE- Sign of the Declination (J2000)
14- 15 I2 deg DEd Degree of Declination (J2000)
17- 18 I2 arcmin DEm Arcminute of Declination (J2000)
20- 24 F5.2 arcsec DEs Arcsecond of Declination (J2000)
26- 31 F6.2 deg GLON Galactic longitude
33- 38 F6.2 deg GLAT Galactic latitude
40- 42 I3 rad/m2 RM Rotation measure
44- 45 I2 rad/m2 e_RM Uncertainty in RM
47- 53 F7.2 mJy PI Debiased polarized flux (1)
55- 62 F8.2 mJy I Total intensity (1)
64- 66 A3 --- S5.2 [Yes/No ] Used in Section 5.2 to determinate
magnetic fields?
68 A1 --- f_S5.2 [abcd] Discarded source (2)
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Note (1): Estimated at the location of the brightest polarized pixel at 20cm.
Note (2): Flag as follows:
a = The source is discarded as it lies within 2° from the Coma Cluster.
b = The source is discarded as its position coincides with the North Polar
Spur region.
c = The source is discarded as it is 3.2σ away from the median of
the RM distribution.
d = The source is discarded as it lies within an anomalous RM region,
indicated in Fig 5.
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 20-Apr-2012