The Complex Large-scale Magnetic Fields in the First Galactic Quadrant as Revealed by the Faraday Depth Profile Disparity

Abstract

The Milky Way is one of the very few spiral galaxies known to host large-scale magnetic field reversals. The existence of the field reversal in the first Galactic quadrant near the Sagittarius spiral arm has been well established, yet poorly characterised due to the insufficient number of reliable Faraday depths (FDs) from extragalactic radio sources (EGSs) through this reversal region. We have therefore performed broadband (1-2 GHz) spectro-polarimetric observations with the Karl G. Jansky Very Large Array (VLA) to determine the FD values of 194 EGSs in the Galactic longitude range of $20^{\circ }$-$52^{\circ }$ within $\pm 5^{\circ }$ from the Galactic mid-plane, covering the Sagittarius arm tangent. This factor of five increase in the EGS FD density has led to the discovery of a disparity in FD values across the Galactic mid-plane in the Galactic longitude range of $40^{\circ }$-$52^{\circ }$. Combined with existing pulsar FD measurements, we suggest that the Sagittarius arm can host an odd-parity disk field. We further compared our newly derived EGS FDs with the predictions of three major Galactic magnetic field models, and concluded that none of them can adequately reproduce our observational results. This has led to our development of new, improved models of the Milky Way disk magnetic field that will serve as an important step towards major future improvements in Galactic magnetic field models.

21 pages main text + 23 pages supplement; MNRAS accepted

References in corpus (26)

• Three Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Polarization Analysis
• The ATNF Pulsar Catalogue
• A New Electron Density Model for Estimation of Pulsar and FRB Distances
• Radio observational constraints on Galactic 3D-emission models
• The Vertical Structure of Warm Ionised Gas in the Milky Way
• The outer scale of turbulence in the magneto-ionized Galactic interstellar medium
• 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
• Pulsar Rotation Measures and Large-scale Magnetic Field Reversals in the Galactic Disk
• New pulsar rotation measures and the Galactic magnetic field
• Low-frequency Faraday rotation measures towards pulsars using LOFAR: probing the 3-D Galactic halo magnetic field
• Detection of microgauss coherent magnetic fields in a galaxy five billion years ago
• Differences in Faraday Rotation Between Adjacent Extragalactic Radio Sources as a Probe of Cosmic Magnetic Fields
• Constraining models of the large scale Galactic magnetic field with WMAP5 polarization data and extragalactic Rotation Measure sources
• A radio-polarisation and rotation measure study of the Gum Nebula and its environment
• Antisymmetry in the Faraday Rotation Sky Caused by a Nearby Magnetized Bubble
• CHANG-ES XIII: Transport processes and the magnetic fields of NGC 4666 - indication of a reversing disk magnetic field
• Magnetic field near the central region of the Galaxy: Rotation measure of extragalactic sources
• Strong excess Faraday rotation on the Inside of the Sagittarius spiral arm
• Through thick or thin: Multiple components of the magneto-ionic medium towards the nearby $\mathrm{H}\mathrm{II}$ region Sharpless 2-27 revealed by Faraday tomography
• A Broadband Spectro-polarimetric View of the NVSS Rotation Measure Catalogue I: Breaking the nπ-ambiguity
• Direction Dependent Corrections in Polarimetric Radio Imaging I : Characterizing the effects of the primary beam on full Stokes imaging
• Constraining the Magnetic Field of the Smith High Velocity Cloud using Faraday rotation
• The GALPROP Cosmic-Ray Propagation Code
• A Broadband Spectro-polarimetric View of the NVSS Rotation Measure Catalogue II: Effects of Off-axis Instrumental Polarisation
• Blazar jet evolution revealed by multi-epoch broadband radio polarimetry