Observability of planet-disc interactions in CO kinematics

TL;DR

This study demonstrates how planet-induced gas kinematic patterns in circumstellar discs can be observed in CO emission lines, enabling indirect detection and mass estimation of embedded planets using ALMA.

Contribution

It introduces a method to identify planet-disc interactions through CO kinematic signatures in simulated hydrodynamical models, aiding in planet detection and characterization.

Findings

Large-scale kinematic perturbations reveal planet presence.

CO line centroid deviations correlate with planet mass.

ALMA can detect these perturbations at high resolution.

Abstract

Empirical evidence of planets in gas-rich circumstellar discs is required to constrain giant planet formation theories. Here we study the kinematic patterns which arise from planet-disc interactions and their observability in CO rotational emission lines. We perform three-dimensional hydrodynamical simulations of single giant planets, and predict the emergent intensity field with radiative transfer. Pressure gradients at planet-carved gaps, spiral wakes and vortices bear strong kinematic counterparts. The iso-velocity contours in the CO(2-1) line centroids $v_\circ$ reveal large-scale perturbations, corresponding to abrupt transitions from below sub-Keplerian to super-Keplerian rotation along with radial and vertical flows. The increase in line optical depth at the edge of the gap also modulates $v_\circ$, but this is a mild effect compared to the dynamical imprint of the planet-disc interaction. The large-scale deviations from the Keplerian rotation thus allow the planets to be indirectly detected via the first moment maps of molecular gas tracers, at ALMA angular resolutions. The strength of these deviations depends on the mass of the perturber. This initial study paves the way to eventually determine the mass of the planet by comparison with more detailed models.