Faraday tomography of LoTSS-DR2 data: I. Faraday moments in the high-latitude outer Galaxy and revealing Loop III in polarisation

Abstract

Observations of synchrotron emission at low radio frequencies reveal a labyrinth of polarised Galactic structures. However, the explanation for the wealth of structures remains uncertain due to the complex interactions between the interstellar medium and the magnetic field. A multi-tracer approach to the analysis of large sky areas is needed. This paper aims to use polarimetric images from the LOFAR Two metre Sky Survey (LoTSS) to produce the biggest mosaic of polarised emission in the northern sky at low radio frequencies (150 MHz) to date. The large area this mosaic covers allows for detailed morphological and statistical studies of polarised structures in the high-latitude outer Galaxy, including the well-known Loop III region. We produced a 3100 square degree Faraday tomographic cube using a rotation measure synthesis tool. We calculated the statistical moments of Faraday spectra and compared them with data sets at higher frequencies (1.4 GHz) and with a map of a rotation measure derived from extragalactic sources. The mosaic is dominated by polarised emission connected to Loop III. Additionally, the mosaic reveals an abundance of other morphological structures, mainly {narrow and extended} depolarisation canals, which are found to be ubiquitous. We find a correlation between the map of an extragalactic rotation measure and the LoTSS first Faraday moment image. The ratio of the two deviates from a simple model of a Burn slab (Burn 1966) along the line of sight, which highlights the high level of complexity in the magnetoionic medium that can be studied at these frequencies.

20 pages, 25 figures, accepted for publication in A&A

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Cited by in corpus (15)

• The Faraday Rotation Measure Grid of the LOFAR Two-metre Sky Survey: Data Release 2
• First look at the multiphase interstellar medium with synthetic observations of low-frequency Faraday tomography
• Faraday tomography of LoTSS-DR2 data: II. Multi-tracer analysis in the high-latitude outer Galaxy
• LOFAR Deep Fields: Probing faint Galactic polarised emission in ELAIS-N1
• Monopole acceleration in intergalactic magnetic fields
• Weakly interacting massive particle cross section limits from LOFAR observations of dwarf spheroidal galaxies
• Faraday moments of the Southern Twenty-centimeter All-sky Polarization Survey (STAPS)
• Associating LOFAR Galactic Faraday structures with the warm neutral medium
• Constraints on the magnetic field in the inter-cluster bridge A399-A401
• Studying the properties of compressible MHD turbulence by synchrotron fluctuation statistics
• A pioneering experiment combining single-antenna and aperture-synthesis data to measure Faraday rotation with GMIMS and the CGPS
• Modeling Local Bubble analogs II: Synthetic Faraday rotation maps
• A three-dimensional reconstruction of the interstellar magnetic field toward a star-forming region
• Non-Gaussian Magnetic Structures in the Small-Scale Turbulent Dynamo
• The contribution of neutral gas to Faraday tomographic data at low frequencies. A first extensive comparison between real and synthetic data