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An exploration of the Zeeman Effect detectability of magnetic substructure in protoplanetary disks

Published onJun 01, 2020
An exploration of the Zeeman Effect detectability of magnetic substructure in protoplanetary disks

Protoplanetary disks (PPDs) are produced from the gravitational collapse and angular momentum mediated flattening of pre-stellar cores (PSCs). PSCs are observed to be moderately magnetized, so PPDs are also expected to be magnetized. Due to the large amount of dynamical processing that occurs during disk information, and imperfect core-scale constraints, predicting the strength and configuration of magnetic fields in PPDs is a difficult theoretical problem. Therefore, observational efforts must play a crucial role in driving forward our understanding of disk-scale magnetic structure. There has been substantial effect put toward observing and interpreting linear polarization in PPDs since the advent of ALMA, but to date this technique has not led to any conclusive magnetic interpretation, largely due to the fact that many other processes beside magnetic alignment (e.g. self-scattering, radiation field alignment, gas flow alignment) have been theorized to be important. Happily, ALMA has a newly commissioned circular polarization (CP) mode that promises to allow use of Zeeman Effect measurements as a complementary technique to access B-field information. Anticipating these data, in this work we perform a theoretical exploration of the expected data products. Using a fiducial disk structure based on AS 209 (a source with favorable observational characteristics that have made it thus far a common choice for ALMA CP programs), we use the POLARIS radiative transfer code to simulate line emission for the hyperfine components of the CN J = 1 - 0 transition. We present mock channel maps and integrated Stokes I and Stokes V profiles for a set of models with a variety of magnetic field and emitting molecule configurations. We also perform a detectability analysis based on the peak flux observed for each of our models. Though there is some dependence on B-field morphology an CN configuration here, we generally expect disks with mean magnetic fields of ~10 mG or higher to be detectable with the current generation of CP instruments.

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