J/ApJ/759/25 Rotation measures at 1.4GHz toward the LMC (Mao+, 2012)
Magnetic field structure of the Large Magellanic Cloud from Faraday
rotation measures of diffuse polarized emission.
Mao S.A., McClure-Griffiths N.M., Gaensler B.M., Haverkorn M., Beck R.,
McConnell D., Wolleben M., Stanimirovic S., Dickey J.M., Staveley-Smith L.
<Astrophys. J., 759, 25 (2012)>
=2012ApJ...759...25M 2012ApJ...759...25M
ADC_Keywords: Magellanic Clouds ; Magnetic fields ; Polarization
Keywords: Magellanic Clouds; magnetic fields; polarization
Abstract:
We present a study of the magnetic field of the Large Magellanic Cloud
(LMC), carried out using diffuse polarized synchrotron emission data
at 1.4GHz acquired at the Parkes Radio Telescope and the Australia
Telescope Compact Array. The observed diffuse polarized emission is
likely to originate above the LMC disk on the near side of the galaxy.
Consistent negative rotation measures (RMs) derived from the diffuse
emission indicate that the line-of-sight magnetic field in the LMC's
near-side halo is directed coherently away from us. In combination
with RMs of extragalactic sources that lie behind the galaxy, we show
that the LMC's large-scale magnetic field is likely to be of
quadrupolar geometry, consistent with the prediction of dynamo theory.
On smaller scales, we identify two brightly polarized filaments
southeast of the LMC, associated with neutral hydrogen arms. The
filaments' magnetic field potentially aligns with the direction toward
the Small Magellanic Cloud (SMC). We suggest that tidal interactions
between the SMC and the LMC in the past 109 years are likely to have
shaped the magnetic field in these filaments.
Description:
Single-dish observations of the LMC were conducted at the Parkes Radio
Telescope over the period 2006 November 20 to November 27 using the
H-OH receiver and the pulsar digital filter bank (PDFB1) with a total
bandwidth of 256MHz, which consisted of 2049 0.125MHz wide channels,
centered on 1384MHz.
Continuum polarimetric data for the LMC at 1.4GHz were recorded as
part of the LMC ATCA HI survey. The details of the observations were
described by Kim et al. (1998ApJ...503..674K 1998ApJ...503..674K). To summarize, the LMC
was observed in mosaic mode consisting of 1300 pointings over the
period 1994 October to 1996 February.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table2.dat 49 305 Rotation measures of extragalactic sources
toward the LMC from ATCA observations
--------------------------------------------------------------------------------
See also:
VII/6 : Polarization of Extragalactic Radio Sources (Eichendorf+ 1980)
J/A+A/549/A56 : Rotation Measure synthesis of WSRT obs. (Iacobelli+, 2013)
J/ApJ/755/21 : Rotation measures of extragalactic radio sources (Mao+, 2012)
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/AJ/138/1243 : The star formation history of the LMC (Harris+, 2009)
J/ApJ/688/1029 : Magnetic field in the SMC (Mao+, 2008)
J/ApJS/45/97 : Extragal. Sources Faraday Rotation (Simard-Normandin+ 1981)
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1 I1 h RAh Hour of right ascension (J2000)
3- 4 I2 min RAm Minute of right ascension (J2000)
6- 10 F5.2 s RAs Second of right ascension (J2000)
12 A1 --- DE- Sign of declination (J2000)
13- 14 I2 deg DEd Degree of declination (J2000)
16- 17 I2 arcmin DEm Arcminute of declination (J2000)
19- 23 F5.2 arcsec DEs Arcsecond of declination (J2000)
25- 28 I4 rad/m2 RM [-161/275] Rotation measure
30- 31 I2 rad/m2 e_RM [1/32] RM uncertainty
33- 37 F5.2 mJy PI [1.5/33.3] De-biased polarized flux
at 1.4GHz (1)
39- 45 F7.2 mJy I [7.4/1240] Total intensity at 1.4GHz (1)
47- 49 A3 --- Fit? [lmc fg] Used in fit? (2)
--------------------------------------------------------------------------------
Note (1): Estimated at the location of the peak pixel.
Note (2): the flag values are:
fg = sources used in the Milky Way foreground rotation measure estimation
lmc = sources whose projection lie directly behind the LMC body
--------------------------------------------------------------------------------
Nomenclature note:
Extragalactic radio sources are <[MMG2012] JHHMMSS.ss+DDMMSS.ss> in Simbad.
History:
From electronic version of the journal
(End) Emmanuelle Perret [CDS] 10-Jul-2014