Tracing magnetic field with synchrotron polarization gradients: parameter study

Abstract

We employ synthetic observations obtained with MHD simulations to study how to trace the distribution of turbulent magnetic fields using the synchrotron polarization gradient techniques suggested by . Both synchrotron polarization gradients and its derivative gradients with regard to the squared wavelength λ 2 are used to explore the probing ability of the technique in magnetic fields from sub-to super-Alfvénic turbulence. We focus on studies that involve multi-frequency measurements in the presence of strong Faraday rotation and show the ways of how to recover the projected mean magnetic fields in the plane of the sky and the local magnetic fields within a tomographic slice. We conclude that the new techniques can successfully reconstruct the 3D magnetic field within our Milky Way and other galaxies. This paper opens an avenue for applying our new techniques to a large number of data cubes such as those from the Low Frequency Array for Radio astronomy and the Square Kilometer Array.

Gradient measurement of synchrotron polarization diagnostic: Application to spatially separated emission and Faraday rotation regions

“…In addition, numerical resolution of data could influence the alignment measurements. We find that the projected magnetic field traced by gradient techniques is not subject to Faraday rotation, which is consistent with the situation for spatially coincident synchrotron polarization radiation and Faraday rotation (Zhang et al 2019a;Zhang, Liu & Lazarian 2019b). A comparison between the directions of projected magnetic field in the emitting-source region and the directions predicted by the gradient measurement of various diagnostics for Case A (see Figure 1).…”

“…The legend P & MF on the right hand indicates the corresponding alignment measure of the 90-degree-rotated synchrotron polarization vector and the projected magnetic field. (Zhang et al 2019a;Zhang, Liu & Lazarian 2019b). Here, polarization radiation in different spatial locations suffers from differential Faraday rotation effects along the LOS.…”

“…Therefore, the purpose of technique development of magnetic field measurement is to extract turbulence information from the integrated observation information. In view of this, we will explore in this paper the new way of studying magnetic field using synchrotron gradients technique (SGT) first proposed in Lazarian et al (2017) and Lazarian & Yuen (2018a), further explored and elaborated in Zhang et al (2019aZhang et al ( , 2019b.…”

“…The ability of SPGs to recover 3D distribution of magnetic field was demonstrated in Lazarian & Yuen (2018a). This new technique has also been applied to tracing projected mean magnetic field direction in super-Alfvénic turbulence regime in terms of multifrequency measurement (Zhang et al 2019a). As a result, SPGs and SIGs become strong counterparts for another technique for magnetic field studies, i.e., velocity gradient technique (González-Casanova & Lazarian 2017;Lazarian & Yuen 2018b).…”

Probing Magnetic Field Morphology in Galaxy Clusters with the Gradient Technique

“…The applicability of GT in tracing the magnetic field morphology has been numerically and observationally tested in many astrophysical environments, including protostars (González-Casanova & Lazarian 2019), molecular clouds (Hu et al 2019b,a;Hsieh et al 2019;Alina et al 2020), galactic diffuse transparent gas Hu et al 2020a,c;Yuen & Lazarian 2017a), and synchrotron emissions from the ISM Lazarian & Yuen 2018b;Ho et al 2019;Zhang et al 2019). Several studies also extend the GT to estimate the magnetization level (Lazarian et al 2018a;, the magnetic field strength (Lazarian et al 2020a) and the sonic Mach number , as well as identifying shocks (Hu et al 2019c) and selfgravitating regions in molecular clouds (Hu et al 2020b).…”