Strong excess Faraday rotation on the Inside of the Sagittarius spiral arm

Abstract

We present first results for Faraday rotation of compact polarized sources (1 to 2 GHz continuum) in The HI/OH/Recombination line (THOR) survey of the inner Galaxy. In the Galactic longitude range 39 degr < l < 52 degr, we find rotation measures in the range -310 rad/m2 < RM < +4219 rad/m2, with the highest values concentrated within a degree of l = 48 degrees 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 degr, RM drops off rapidly, while at l < 47 degr, the mean RM is higher with a larger standard deviation than at l > 49 degr. 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.

Accepted for publication in Astrophysical Journal Letters

References in corpus (18)

• The ATNF Pulsar Catalogue
• A single fast radio burst localized to a massive galaxy at cosmological distance
• The VLA Galactic Plane Survey
• The Vertical Structure of Warm Ionised Gas in the Milky Way
• Rotation Measures of Extragalactic Sources Behind the Southern Galactic Plane: New Insights into the Large-Scale Magnetic Field of the Inner Milky Way
• Estimating extragalactic Faraday rotation
• The Southern Galactic Plane Survey: Polarized Radio Continuum Observations and Analysis
• Pulsar Rotation Measures and Large-scale Magnetic Field Reversals in the Galactic Disk
• Catalog of observed tangents to the spiral arms in the Milky Way galaxy
• A radio-polarisation and rotation measure study of the Gum Nebula and its environment
• Three-Dimensional Simulations of Magnetized Superbubbles: New Insights into the Importance of MHD Effects on Observed Quantities
• S-PASS/ATCA: a window on the magnetic universe in the southern hemisphere
• Massive Star Forming Regions in the Galaxy using the Spitzer GLIMPSE Survey
• A Broadband Spectro-polarimetric View of the NVSS Rotation Measure Catalogue I: Breaking the nπ-ambiguity
• Detecting Pulsars with Interstellar Scintillation in Variance Images
• Polarization shadows of extragalactic sources by the local magneto-ionic ISM
• Survey of Ionized Gas of the Galaxy, Made with the Arecibo telescope (SIGGMA): Inner Galaxy Data Release
• Ionized gas in the Scutum spiral arm as traced in [N II] and [C II]

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• RMTable2023 and PolSpectra2023: standards for reporting polarization and Faraday rotation measurements of radio sources
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