J/ApJ/755/21 Rotation measures of extragalactic radio sources (Mao+, 2012)
New constraints on the Galactic halo magnetic field using rotation measures of
extragalactic sources toward the outer Galaxy.
Mao S.A., McClure-Griffiths N.M., Gaensler B.M., Brown J.C., van Eck C.L.,
Haverkorn M., Kronberg P.P., Stil J.M., Shukurov A., Taylor A.R.
<Astrophys. J., 755, 21 (2012)>
=2012ApJ...755...21M 2012ApJ...755...21M
ADC_Keywords: Radio sources ; Magnetic fields ; Milky Way ; Polarization ;
Galactic plane
Keywords: Galaxy: halo; ISM: magnetic fields; polarization
Abstract:
We present a study of the Milky Way disk and halo magnetic field,
determined from observations of Faraday rotation measure (RM) toward
641 polarized extragalactic radio sources in the Galactic longitude
range 100°-117°, within 30° of the Galactic plane. For
|b|<15°, we observe a symmetric RM distribution about the Galactic
plane. This is consistent with a disk field in the Perseus arm of even
parity across the Galactic mid-plane. In the range
15°<|b|<30°, we find median RMs of -15±4rad/m2 and
-62±5rad/m2 in the northern and southern Galactic hemispheres,
respectively. If the RM distribution is a signature of the large-scale
field parallel to the Galactic plane, then this suggests that the halo
magnetic field toward the outer Galaxy does not reverse direction
across the mid-plane. The variation of RM as a function of Galactic
latitude in this longitude range is such that RMs become more negative
at larger |b|. This is consistent with an azimuthal magnetic field of
strength 2µG (7µG) at a height 0.8-2kpc above (below) the
Galactic plane between the local and the Perseus spiral arm. We
propose that the Milky Way could possess spiral-like halo magnetic
fields similar to those observed in M51.
Description:
Observations of the selected polarized extragalactic radio sources
were conducted at the VLA on 2008 June 8th and 23rd, July 7th and 8th,
August 26th and 31st, and September 1st and 2nd in D and DnC
configurations. Data were taken in two 25MHz bands in the spectral
line mode. Each band consists of seven 3.125MHz wide channels (with an
edge channel discarded), centered at 1365MHz and 1486MHz,
respectively.
This work also makes use of 339 extragalactic radio sources rotation
measures in the Canadian Galactic Plane Survey (CGPS) latitude
extension region (100°<l<117°, -3.5°<b<+18°; J. C.
Brown et al. in preparation).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 46 302 Rotation measures of extragalactic sources from VLA
observations in increasing order of Galactic longitude
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See also:
VIII/65 : 1.4GHz NRAO VLA Sky Survey (NVSS) (Condon+ 1998)
VII/6 : Polarization of Extragalactic Radio Sources (Eichendorf+ 1980)
J/A+A/549/A56 : Rotation Measure synthesis of WSRT obs. (Iacobelli+, 2013)
J/ApJ/749/71 : Star polarization in the Galactic plane (Pavel+, 2012)
J/ApJ/728/97 : VLA rotation measures in the Galactic plane (Van Eck+, 2011)
J/A+A/513/A65 : RMs in the fourth Galactic quadrant (Nota+, 2010)
J/ApJ/714/1170 : Faraday rotation at high Galactic latitude (Mao+, 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 : RMs 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/ApJS/45/97 : Extragal. Radio Sources Faraday Rot. (Simard-Normandin+ 1981)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 2 I2 h RAh [0/23] 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 declination (J2000)
14- 15 I2 deg DEd [29/84] Degree of declination (J2000)
17- 18 I2 arcmin DEm Arcminute of declination (J2000)
20- 21 I2 arcsec DEs Arcsecond of declination (J2000)
22- 24 A3 --- --- [.00]
26- 31 F6.2 deg GLON [100.06/116.95] Galactic longitude
33- 38 F6.2 deg GLAT [-29.95/29.97] Galactic latitude
40- 43 I4 rad/m2 RM [-514/336] Rotation measure
45- 46 I2 rad/m2 e_RM [1/37] RM uncertainty
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History:
From electronic version of the journal
(End) Emmanuelle Perret [CDS] 06-Mar-2014