Spiral excitation in protoplanetary disks through gap-edge illumination: Distinctive kinematic signatures in CO isotopologues

TL;DR

This study compares shadow-driven and planet-driven spiral formation in protoplanetary disks through hydrodynamical simulations, revealing distinctive CO kinematic signatures that can help identify the underlying mechanism.

Contribution

It introduces a simulation-based method to distinguish between shadow-driven and planet-driven spirals using CO kinematic signatures in protoplanetary disks.

Findings

Shadow-driven spirals produce prominent two-armed features in CO moment-1 maps.

Standard planet-driven spirals lack these specific CO kinematic signatures.

Vertical velocities are key indicators of shadow-driven spiral formation.

Abstract

High-resolution, near-infrared observations have revealed prominent, two-armed spirals in a multitude of systems, such as MWC~758, SAO~206462, and V1247~Ori. Alongside the classical theory of disk-companion interaction, shadow-based driving has come into vogue as a potential explanation for such large-scale substructures. How might these two mechanisms be distinguished from one another in observations? To investigate this question, we ran a pair of hydrodynamical simulations with \texttt{PLUTO}. One, with full radiation hydrodynamics and gas-grain collision, was designed to develop shadow-driven spirals at the outer gap edge of a sub-thermal, Saturn-mass planet. The other, with parametrized $\beta$-cooling, was set up to capture the more standard view of spiral wave excitation by a super-thermal, multi-Jupiter-mass, exterior planetary companion. Post-processing of these simulations with the Monte Carlo radiative transfer (MCRT) code \texttt{RADMC3D} revealed that strong vertical velocities in the shadow-driven case create a prominent two-armed feature in the moment-1 CO maps, particularly when the disk is viewed face-on in optically thicker isotopologues; such a feature is not seen in the standard planet-driven case. Conversely, the presence or absence of such signatures in two-armed spiral systems would distinguish those potentially driven by exterior, multi-Jupiter-mass companions, and thus help identify promising targets for future direct-imaging campaigns.