Gas vs dust radial extent in disks: the importance of their thermal interplay

TL;DR

This paper investigates how the thermal interplay between gas and dust affects their radial extents in protoplanetary disks, emphasizing the roles of dust grain size, optical depth, and thermal decoupling.

Contribution

It introduces models that incorporate realistic dust grain size distributions and their feedback on gas emission, highlighting the importance of thermal structure in disk evolution.

Findings

Dust and gas extents differ mainly due to optical depth differences.

Radial drift causes a sharp decrease in intensity at the disk's outer edge.

Thermal decoupling occurs between gas and dust at intermediate heights.

Abstract

A key parameter governing the secular evolution of protoplanetary disks is their outer radius. In this paper, the feedback of realistic dust grain size distributions onto the gas emission is investigated. Models predict that the difference of dust and gas extents as traced by CO is primarily caused by differences in the optical depth of lines vs continuum. The main effect of radial drift is the sharp decrease in the intensity profile at the outer edge. The gas radial extent can easily range within a factor of 2 for models with different turbulence. A combination of grain growth and vertical settling leads to thermal de-coupling between gas and dust at intermediate scale-heights. A proper treatment of the gas thermal structure within dust gaps will be fundamental to disentangle surface density gaps from gas temperature gaps.