Gap Opening in Protoplanetary Disks: Gas Dynamics from Global Non-ideal MHD Simulations with Consistent Thermochemistry

TL;DR

This paper uses advanced 2D non-ideal MHD simulations with thermochemistry to explore how planets open gaps in protoplanetary disks, revealing magnetic and chemical signatures observable by ALMA.

Contribution

It introduces the first 2D global non-ideal MHD simulations with thermochemistry for planet gap-opening, highlighting magnetic flux concentration and meridional circulation effects.

Findings

Magnetic flux concentrates in planet-opened gaps.

Fast meridional gas circulation occurs near gap edges.

Gaps show higher ionization and molecular ion abundance.

Abstract

Recent high angular resolution ALMA observations have revealed numerous gaps in protoplanetary disks. A popular interpretation has been that planets open them. Most previous investigations of planet gap-opening have concentrated on viscous disks. Here, we carry out 2D (axisymmetric) global simulations of gap opening by a planet in a wind-launching non-ideal MHD disk with consistent thermochemistry. We find a strong concentration of poloidal magnetic flux in the planet-opened gap, where the gas dynamics are magnetically dominated. The magnetic field also drives a fast (nearly sonic) meridional gas circulation in the denser disk regions near the inner and outer edges of the gap, which may be observable through high-resolution molecular line observations. The gap is more ionized than its denser surrounding regions, with a better magnetic field-matter coupling. In particular, it has a much higher abundance of molecular ion HCO$^+$, consistent with ALMA observations of the well-studied AS 209 protoplanetary disk that has prominent gaps and fast meridional motions reaching the local sound speed. Finally, we provide fitting formulae for the ambipolar and Ohmic diffusivities as a function of the disk local density, which can be used for future 3D simulations of planet gap-opening in non-ideal MHD disks where thermochemistry is too computationally expensive to evolve self-consistently with the magneto-hydrodynamics.