Strong Excess Faraday Rotation on the Inside of the Sagittarius Spiral Arm

R. Shanahan; S. J. Lemmer; J. M. Stil; H. Beuther; Y. Wang; J. Soler; L. D. Anderson; F. Bigiel; S. C.O. Glover; P. Goldsmith; R. S. Klessen; N. M. McClure-Griffiths; S. Reissl; M. Rugel; R. J. Smith

doi:10.3847/2041-8213/ab58d4

Strong Excess Faraday Rotation on the Inside of the Sagittarius Spiral Arm

R. Shanahan, S. J. Lemmer, J. M. Stil, H. Beuther, Y. Wang, J. Soler, L. D. Anderson, F. Bigiel, S. C.O. Glover, P. Goldsmith, R. S. Klessen, N. M. McClure-Griffiths, S. Reissl, M. Rugel, R. J. Smith

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Abstract

We present first results for Faraday rotation of compact polarized sources (1-2 GHz continuum) in The H i/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-310 rad m^-2 ≤ RM ≤ +4219 rad m^-2, 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 H ii 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.

Original language	English
Article number	L7
Journal	Astrophysical Journal Letters
Volume	887
Issue number	1
DOIs	https://doi.org/10.3847/2041-8213/ab58d4
Publication status	Published - 10 Dec 2019

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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. (2019). Strong Excess Faraday Rotation on the Inside of the Sagittarius Spiral Arm. Astrophysical Journal Letters, 887(1), Article L7. https://doi.org/10.3847/2041-8213/ab58d4

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abstract = "We present first results for Faraday rotation of compact polarized sources (1-2 GHz continuum) in The H i/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-310 rad m-2 ≤ RM ≤ +4219 rad m-2, 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 H ii 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.",

author = "R. Shanahan and Lemmer, {S. J.} and Stil, {J. M.} and H. Beuther and Y. Wang and J. Soler and Anderson, {L. D.} and F. Bigiel and Glover, {S. C.O.} and P. Goldsmith and Klessen, {R. S.} and McClure-Griffiths, {N. M.} and S. Reissl and M. Rugel and Smith, {R. J.}",

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T1 - Strong Excess Faraday Rotation on the Inside of the Sagittarius Spiral Arm

AU - Shanahan, R.

AU - Lemmer, S. J.

AU - Stil, J. M.

AU - Beuther, H.

AU - Wang, Y.

AU - Soler, J.

AU - Anderson, L. D.

AU - Bigiel, F.

AU - Glover, S. C.O.

AU - Goldsmith, P.

AU - Klessen, R. S.

AU - McClure-Griffiths, N. M.

AU - Reissl, S.

AU - Rugel, M.

AU - Smith, R. J.

PY - 2019/12/10

Y1 - 2019/12/10

N2 - We present first results for Faraday rotation of compact polarized sources (1-2 GHz continuum) in The H i/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-310 rad m-2 ≤ RM ≤ +4219 rad m-2, 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 H ii 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.

AB - We present first results for Faraday rotation of compact polarized sources (1-2 GHz continuum) in The H i/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-310 rad m-2 ≤ RM ≤ +4219 rad m-2, 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 H ii 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.

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DO - 10.3847/2041-8213/ab58d4

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SN - 2041-8205

VL - 887

JO - Astrophysical Journal Letters

JF - Astrophysical Journal Letters

IS - 1

M1 - L7

ER -

Strong Excess Faraday Rotation on the Inside of the Sagittarius Spiral Arm

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