Untangling Magnetic Complexity in Protoplanetary Disks with the Zeeman Effect

Abstract

With the recent advent of circular polarization capabilities at the Atacama Large Millimeter/submillimeter Array (ALMA), Zeeman effect measurements of spectral lines are now possible as a means to directly probe line-of-sight magnetic fields in protoplanetary disks (PPDs). We present a modeling study that aims to guide physical interpretation of these anticipated observations. Using a fiducial density structure based on a typical ringed disk, we simulate line emission for the hyperfine components of the CN $J=1-0$ transition with the POLARIS radiative transfer code. Since the expected magnetic field and typical CN distribution in PPDs remain largely unconstrained, we produce models with several different configurations. Corresponding integrated Stokes $I$ and $V$ profiles and 0.4 km/s resolution, 1'' beam convolved channel maps are presented. We demonstrate that the emission signatures from toroidally dominated magnetic fields are distinguishable from vertically dominated magnetic field based on channel map morphology. Due to line-of-sight and beam cancellation effects, disks with toroidal $\mathbf{B}$-field configurations result in significantly diminished Stokes $V$ emission. Complex magnetic fields therefore render the traditionally used method for inferring line-of-sight magnetic field strengths (i.e., fitting the derivative of the Stokes $I$ to the Stokes $V$ profile) ambiguous, since a given intrinsic field strength can yield a variety of Stokes $V$ amplitudes depending on the magnetic field geometry. In addition, gas gaps can create structure in the integrated Stokes $V$ profile that might mimic magnetic substructure. This method should therefore be applied with caution in PPD environments, and can only confidently be used as a measure of magnetic field strength if the disk's magnetic field configuration is well understood.

arXiv comment20 pages, 11 figures. Accepted for publication in ApJ

References in corpus (35)

• An atomic and molecular database for analysis of submillimetre line observations
• The Disk Substructures at High Angular Resolution Project (DSHARP): I. Motivation, Sample, Calibration, and Overview
• Protoplanetary Disk Structures in Ophiuchus
• Radiative torques: Analytical Model and Basic Properties
• Magnetic Fields in the Formation of Sun-Like Stars
• Zonal Flows and Long-Lived Axisymmetric Pressure Bumps in Magnetorotational Turbulence
• Radiative Equilibrium and Temperature Correction in Monte Carlo Radiation Transfer
• Disks ARound TTauri Stars with Sphere (DARTTS-S) I: Sphere / IRDIS Polarimetric Imaging of 8 prominent TTauri Disks
• Probing the structure of protoplanetary disks: a comparative study of DM Tau, LkCa 15 and MWC 480
• Weak Turbulence in the HD 163296 Protoplanetary Disk Revealed by ALMA CO Observations
• Millimeter-wave polarization of protoplanetary disks due to dust scattering
• Magnetic Fields in Dark Cloud Cores: Arecibo OH Zeeman Observations
• Constraining the X-ray and Cosmic Ray Ionization Chemistry of the TW Hya Protoplanetary Disk: Evidence for a Sub-interstellar Cosmic Ray Rate
• MHD simulations of jet acceleration from Keplerian accretion disks: the effects of disk resistivity
• A multi-wavelength analysis for interferometric (sub-)mm observations of protoplanetary disks: radial constraints on the dust properties and the disk structure
• Turbulence In the Outer Regions of Protoplanetary Disks. II. Strong Accretion Driven by a Vertical Magnetic Field
• Radiative transfer with POLARIS: I. Analysis of magnetic fields through synthetic dust continuum polarization measurements
• ALMA continuum observations of the protoplanetary disk AS 209. Evidence of multiple gaps opened by a single planet
• Disk Imaging Survey of Chemistry with SMA: II. Southern Sky Protoplanetary Disk Data and Full Sample Statistics
• The evidence of radio polarization induced by the radiative grain alignment and self-scattering of dust grains in a protoplanetary disk
• Inclination-Induced Polarization of Scattered Millimeter Radiation from Protoplanetary Disks: The Case of HL Tau
• Wind-driven Accretion in Protoplanetary Disks --- II: Radial Dependence and Global Picture
• Radiative grain alignment in protoplanetary disks: Implications for polarimetric observations
• Grain Alignment and Polarized Emission from Magnetized T Tauri Disks
• CN rings in full protoplanetary disks around young stars as probes of disk structure
• Chemistry in Disks. V: CN and HCN in proto-planetary disks
• Stringent limits on the magnetic field strength in the disc of TW Hya: ALMA observations of CN polarisation
• MRI-driven Accretion on to Magnetized stars: Global 3D MHD Simulations of Magnetospheric and Boundary Layer Regimes
• ALMA resolves the hourglass magnetic field in G31.41+0.31
• Rings and gaps produced by variable magnetic disk winds and avalanche accretion streams: I. Axisymmetric resistive MHD simulations
• Gas density perturbations induced by forming planet(s) in the AS 209 protoplanetary disk as seen with ALMA
• Magnetic fields in protoplanetary disks: from MHD simulations to ALMA observations
• Tracing planet-induced structures in circumstellar disks using molecular lines
• Millimeter-wave polarization due to grain alignment by the gas flow in protoplanetary disks
• Magnetic fields in molecular clouds: Limitations of the analysis of Zeeman observations

Cited by in corpus (3)

• Global Three-Dimensional Simulations of Outer Protoplanetary Disks with Ambipolar Diffusion
• ALMA CN Zeeman Observations of AS 209: Limits on Magnetic Field Strength and Magnetically Driven Accretion Rate
• Three-dimensional magnetic field imaging of protoplanetary disks using Zeeman broadening and linear polarization observations