J/ApJ/887/L7 Faraday rotation of radio sources from THOR (Shanahan+, 2019)
Strong excess Faraday rotation on the inside of the Sagittarius spiral arm.
Shanahan R., Lemmer S.J., Stil J.M., Beuther H., Wang Y., Soler J.,
Anderson L.D., Bigiel F., Glover S.C.O., Goldsmith P., Klessen R.S.,
McClure-Griffiths N.M., Reissl S., Rugel M., Smith R.J.
<Astrophys. J., 887, L7 (2019)>
=2019ApJ...887L...7S 2019ApJ...887L...7S
ADC_Keywords: Radio sources; Magnetic fields; Polarization; H II regions
Keywords: Galaxy magnetic fields ; Polarimetry ; Interstellar medium ;
Spiral arms ; Transient sources ; H II regions ; Radio pulsars
Abstract:
We present first results for Faraday rotation of compact polarized
sources (1-2GHz continuum) in The HI/OH/Recombination line (THOR)
survey of the inner Galaxy. In the Galactic longitude range
39°<l<52°, we find rotation measures (RMs) in the range
-310rad/m2≤RM≤+4219rad/m2, with the highest values concentrated
within a degree of l=48° at the Sagittarius arm tangent. Most of
the high RMs arise in diffuse plasma, along lines of sight that do not
intersect HII regions. For l>49°, RM drops off rapidly, while at
l<47°, the mean RM is higher with a larger standard deviation than
at l>49°. We attribute the RM structure to the compressed diffuse
warm ionized medium in the spiral arm, upstream of the major star
formation regions. The Sagittarius arm acts as a significant Faraday
screen inside the Galaxy. This has implications for models of the
Galactic magnetic field and the expected amount of Faraday rotation of
fast radio bursts from their host galaxies. We emphasize the
importance of sensitivity to high Faraday depth in future polarization
surveys.
Description:
The HI/OH/Recombination line (THOR) survey (Beuther+ 2016A&A...595A..32B 2016A&A...595A..32B)
covers the inner Galaxy in the longitude range 14.5°<l<67.4°
and latitude -1.25°<b<1.25° with the Karl G. Jansky Very Large
Array (VLA) in C configuration in L band (1-2GHz). The survey includes
the 21cm line of atomic hydrogen, OH lines, several radio
recombination lines, and the continuum in 512 channels from 1 to 2GHz.
The 21cm line and total intensity continuum were combined with
archival data from the VLA Galactic Plane Survey (VGPS;
Stil+ 2006AJ....132.1158S 2006AJ....132.1158S) and the Effelsberg continuum survey by
Reich+ (1990, J/A+AS/83/539) at 1.4GHz only.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 122 127 Rotation measure detections
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See also:
B/psr : ATNF Pulsar Catalogue (Manchester+, 2005)
VIII/65 : 1.4GHz NRAO VLA Sky Survey (NVSS) (Condon+ 1998)
J/A+AS/83/539 : 21cm radio continuum survey. I. (Reich+ 1990)
J/ApJS/145/213 : Rotation measures of compact sources in CGPS (Brown+, 2003)
J/ApJ/663/258 : RMs of extragalactic sources in SGPS (Brown+, 2007)
J/ApJ/702/1230 : Rotation measure image of the sky (Taylor+, 2009)
J/ApJ/719/1104 : Massive star forming complexes in GLIMPSE (Rahman+, 2010)
J/ApJ/720/1055 : VBLA observations of W51 Main/South (Sato+, 2010)
J/ApJS/194/32 : HII Region Discovery Survey (HRDS). II. (Anderson+, 2011)
J/ApJ/728/97 : VLA rotation measures in the Galactic plane (Van Eck+, 2011)
J/ApJS/212/1 : The WISE catalog of Galactic HII regions (Anderson+, 2014)
J/A+A/588/A97 : Continuum sources from the THOR survey (Bihr+, 2016)
J/MNRAS/469/4034 : Broadband polarisation of radio AGN (O'Sullivan+, 2017)
J/ApJS/234/11 : Pulsar rotation measures (Han+, 2018)
J/A+A/619/A124 : THOR survey in northern Galactic plane (Wang+, 2018)
J/ApJS/240/14 : SIGGMA: inner galaxy data release (Liu+, 2019)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 13 A13 --- [BJB2016] Name from Wang+ (2018, J/A+A/619/A124)
15- 21 F7.1 mJy S [9.2/1021.6]? Flux density
from Wang+ (2018, J/A+A/619/A124) (1)
25- 29 F5.2 --- alpha [-1.41/0.35]? Spectral index
from Wang+ (2018, J/A+A/619/A124) (1)
32- 36 F5.2 % fP [0.94/20.33] Fractional polarization
41- 44 I4 rad/m2 RM [-310/4219] Rotation Measure
47- 48 I2 rad/m2 e_RM [1/95] Error in Rotation measure
50- 64 A15 --- HII1 Nearest HII region by relative distance (2)
66- 71 F6.1 arcmin d1 [0.6/2601.1] Angular distance for HII1
74- 78 F5.1 --- d1rel [0.3/8.4] Distance divided
by HII1 region radius
80- 94 A15 --- HII2 Nearest HII region by angular distance (3)
96-101 F6.1 arcmin d2 [0.6/43.3] Angular distance for HII2
103-108 F6.1 --- d2rel [0.3/59.6] Distance divided
by HII2 region radius
110-115 F6.3 deg GLON [39/52.3] Galactic Longitude
117-122 F6.3 deg GLAT [-1.12/1.24] Galactic Latitude
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Note (1): Columns "S" and "alpha" do not contain a value if the polarization
is listed for a sub-component of a resolved source in the catalog of
Wang+ (2018, J/A+A/619/A124). The source ID is derived from the
position at which the rotation measure is extracted.
Note (2): Column "HII1" lists the name of the nearest HII region in the
catalog of Anderson+ (2014, J/ApJS/212/1 --
<[ABB2014] WISE GLLL.lll+BB.bbb> in Simbad), when selected by the ratio
of angular distance to the radius of the HII region.
Note (3): Column "HII2" lists the name of the nearest HII region in the
catalog of Anderson+ (2014, J/ApJS/212/1 --
(<[ABB2014] WISE GLLL.lll+BB.bbb> in Simbad), when selected by
angular distance.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 31-May-2021