Investigating Protoplanetary Disk Cooling through Kinematics: Analytical GI Wiggle

TL;DR

This paper analytically investigates how gravitational instability in young protostellar disks creates kinematic signatures, especially spiral wave perturbations, which can be used to infer disk cooling properties from high-resolution observations.

Contribution

It provides an analytical framework to identify and interpret kinematic signatures of gravitational instability in protoplanetary disks, linking them to cooling processes.

Findings

Unstable disks exhibit distinct velocity deviations from Keplerian rotation.

Kinematic signatures depend on disk parameters and cooling factor.

Detection of these features constrains disk cooling mechanisms.

Abstract

It is likely that young protostellar disks undergo a self-gravitating phase. Such systems are characterized by the presence of a spiral pattern that can be either in a quasi-steady state or in a nonlinear unstable condition. This spiral wave affects both the gas dynamics and kinematics, resulting in deviations from the Keplerian rotation. Recently, a lot of attention has been devoted to kinematic studies of planet-forming environments, and we are now able to measure even small perturbations of velocity field ($\lesssim 1 \%$ of the Keplerian speed) thanks to high spatial and spectral resolution observations of protostellar disks. In this work, we investigate the kinematic signatures of gravitational instability: we perform an analytical study of the linear response of a self-gravitating disk to a spiral-like perturbation, focusing our attention on the velocity field perturbations. We show that unstable disks have clear kinematic imprints into the gas component across the entire disk extent, due to the GI spiral wave perturbation, resulting in deviations from Keplerian rotation. The shape of these signatures depends on several parameters, but they are significantly affected by the cooling factor: by detecting these features, we can put constraints on protoplanetary disk cooling.