Constraining regular and turbulent magnetic field strengths in M51 via Faraday depolarization

Abstract

We employ an analytical model that incorporates both wavelength-dependent and wavelength-independent depolarization to describe radio polarimetric observations of polarization at $\lambda \lambda \lambda 3.5,6.2,20.5$ cm in M51 (NGC 5194). The aim is to constrain both the regular and turbulent magnetic field strengths in the disk and halo, modeled as a two- or three-layer magneto-ionic medium, via differential Faraday rotation and internal Faraday dispersion, along with wavelength-independent depolarization arising from turbulent magnetic fields. A reduced chi-squared analysis is used for the statistical comparison of predicted to observed polarization maps to determine the best-fit magnetic field configuration at each of four radial rings spanning $2.4-7.2$ kpc in $1.2$ kpc increments. We find that a two-layer modeling approach provides a better fit to the observations than a three-layer model, where the near and far sides of the halo are taken to be identical, although the resulting best-fit magnetic field strengths are comparable. This implies that all of the signal from the far halo is depolarized at these wavelengths. We find a total magnetic field in the disk of approximately $18\mu$G and a total magnetic field strength in the halo of $\sim 4-6\mu$G. Both turbulent and regular magnetic field strengths in the disk exceed those in the halo by a factor of a few. About half of the turbulent magnetic field in the disk is anisotropic, but in the halo all turbulence is only isotropic.

arXiv commentAccepted for publication in Astronomy & Astrophysics, 10 pages, 5 figures, 5 tables

References in corpus (15)

• The Interstellar Environment of our Galaxy
• Magnetic fields and spiral arms in the galaxy M51
• The Westerbork SINGS Survey II. Polarization, Faraday Rotation, and Magnetic Fields
• Magnetism in the spiral galaxy NGC 6946: magnetic arms, depolarization rings, dynamo modes and helical fields
• A new interpretation of the far-infrared - radio correlation and the expected breakdown at high redshift
• The Radio Continuum-Star Formation Rate Relation in WSRT SINGS Galaxies
• High-resolution radio continuum survey of M33: III. Magnetic fields
• The Westerbork SINGS survey III. Global magnetic field topology
• Multi-scale Radio-IR Correlations in M31 and M33: The Role of Magnetic Fields and Star Formation
• New Constraints on the Galactic Halo Magnetic Field using Rotation Measures of Extragalactic Sources Towards the Outer Galaxy
• Characterizing Magnetized Turbulence in M51
• Magnetic fields in the Milky Way and other spiral galaxies
• The Role of Magnetic Fields in Spiral Galaxies
• Depolarization of synchrotron radiation in a multilayer magneto-ionic medium
• A Lack of Resolved Near-Infrared Polarization Across the Face of M51

Cited by in corpus (10)

• The nature of the low-frequency emission of M51: First observations of a nearby galaxy with LOFAR
• CHANG-ES XV: Large-scale magnetic field reversals in the radio halo of NGC 4631
• Properties of the Magneto-ionic Medium in the Halo of M51 revealed by Wide-band Polarimetry
• Supernova-regulated ISM -- V. Space- and time-correlations
• The magnetized disk-halo transition region of M51
• The Magnetized Disk-Halo Transition Region of M51
• Wiggle Instability of Galactic Spiral Shocks: Effects of Magnetic Fields
• CMB foreground measurements through broad-band radio spectro-polarimetry: prospects of the SKA-MPG telescope
• Pseudo-observation of spiral galaxies in the radio band to verify depolarization models
• Workshop summary 'The Power of Faraday Tomography'