Mapping the 3D Kinematical Structure of the Gas Disk of HD 169142

TL;DR

This study uses ALMA CO observations to identify a meridional flow at 125 au in the disk of HD 169142, suggesting the presence of an embedded planet and revealing complex gas dynamics and structure responses in the disk.

Contribution

It introduces a new method to analyze gas kinematics and physical structure in protoplanetary disks, providing insights into planet-disk interactions and gap formation.

Findings

Detected a meridional flow at 125 au in the disk.

Found increased gas pressure regions despite surface density minima.

Developed an analytical model linking surface density changes to physical structure responses.

Abstract

The disk around HD 169142 has been suggested to host multiple embedded planets due to the range of structures observed in the dust distributions. We analyze archival ALMA observations of $^{12} \mathrm{CO \ (2-1)}$, $^{13} \mathrm{CO \ (2-1)}$, and $\mathrm{C}^{18} \mathrm{O \ (2-1)}$ to search for large-scale kinematic structures associated with other embedded planets in the outer disk. At 125 au, we identify a coherent flow from the disk surface to the midplane, traced by all three CO isotopologues, and interpret it as a meridional flow, potentially driven by an embedded planet. We use changes in the rotation speed of the gas to characterize the physical structure across this region, finding that at 125 au the CO emission traces regions of increased gas pressure, despite being at a surface density minimum. Developing a simple analytical model, we demonstrate that the physical structure of the gap can have non-trivial responses to changes in the surface density, consistent both with previous thermo-chemical models, and the conditions inferred observationally. Applying this technique to a range of sources will allow us to directly confront theoretical models of gap-opening in protoplanetary disks.