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An in-depth investigation of faraday depth spectrum using synthetic observations of turbulent mhd simulations

Lookup NU author(s): Andrew Fletcher

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This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).


Abstract

© 2019 by the authors.In this paper, we present a detailed analysis of the Faraday depth (FD) spectrum and its clean components obtained through the application of the commonly used technique of Faraday rotation measure synthesis to analyze spectro-polarimetric data. To directly compare the Faraday depth spectrum with physical properties of a magneto-ionic medium, we generated synthetic broad-bandwidth spectro-polarimetric observations from magnetohydrodynamic (MHD) simulations of a transonic, isothermal, compressible turbulent medium. We find that correlated magnetic field structures give rise to a combination of spiky, localized peaks at certain FD values, and broad structures in the FD spectrum. Although most of these spiky FD structures appear narrow, giving an impression of a Faraday thin medium, we show that they arise from strong synchrotron emissivity at that FD. Strong emissivity at a FD can arise because of both strong spatially local polarized synchrotron emissivity at a FD or accumulation of weaker emissions along the distance through a medium that have Faraday depths within half the width of the rotation measure spread function. Such a complex Faraday depth spectrum is a natural consequence of MHD turbulence when the lines of sight pass through a few turbulent cells. This therefore complicates the convention of attributing narrow FD peaks to the presence of a Faraday-rotating medium along the line of sight. Our work shows that it is difficult to extract the FD along a line of sight from the Faraday depth spectrum using standard methods for a turbulent medium in which synchrotron emission and Faraday rotation occur simultaneously.


Publication metadata

Author(s): Basu A, Fletcher A, Mao SA, Burkhart B, Beck R, Schnitzeler D

Publication type: Article

Publication status: Published

Journal: Galaxies

Year: 2019

Volume: 7

Issue: 4

Online publication date: 23/11/2019

Acceptance date: 18/11/2019

Date deposited: 17/02/2020

ISSN (electronic): 2075-4434

Publisher: MDPIAG

URL: https://doi.org/10.3390/galaxies7040089

DOI: 10.3390/galaxies7040089


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