Observational Signatures of Disk Winds in Protoplanetary Disks: Differentiating Magnetized and Photoevaporative Outflows With Fully Coupled Thermochemistry

TL;DR

This study uses advanced simulations to identify observational signatures that distinguish magnetized from photoevaporative winds in protoplanetary disks, aiding understanding of disk evolution and planet formation.

Contribution

It provides the first detailed synthetic ALMA observations differentiating magnetized and photoevaporative disk winds based on thermochemical and dynamical signatures.

Findings

Magnetized winds are colder, denser, and exhibit super-Keplerian rotation.

Photoevaporative winds are hotter, less dense, and show sub-Keplerian rotation.

Observable differences in CO and [C I] emissions can distinguish wind types.

Abstract

Magnetized winds and photoevaporative winds are critical in shaping protoplanetary disk evolution. Using 2D axisymmetric (magneto-)hydrodynamic simulations with Athena++ implementing fully coupled thermochemistry, we investigate the signatures of the two winds in CO and [C~I] ALMA observations, and examine the potential to distinguish the origins. Our simulations reveal fundamental differences between the two winds: magnetized winds are colder and denser, exhibiting super-Keplerian rotation with small poloidal velocities of $\lesssim 1~{\rm km~s}^{-1}$ in the atmosphere ($z/R\gtrsim0.45$), while photoevaporative winds are hotter and less dense, exhibiting sub-Keplerian rotation with higher poloidal velocity of several ${\rm km~s}^{-1}$. In addition to previously identified factors like thermal pressure gradient and disk's self-gravity, we demonstrate that magnetic tension/pressure and advection significantly influence rotational velocities of the gas in the wind, which lead to emission patterns that are distinct from Keplerian rotation in synthetic ALMA observations. Magnetized winds are visible in CO channel maps when wind loss rates are $\gtrsim10^{-8}~M_\odot~{\rm yr}^{-1}$. When wind loss rates are lower, magnetized winds produce subtle perturbations in channel maps, which resemble the so-called ``velocity kinks'' produced by protoplanets. While photoevaporative winds dissociate CO through strong XUV radiation and thus are weaker in CO, they can create observable ring-like substructures. [C~I] emission is optically thin and could be most effective at detecting both winds in disks with high gas mass and/or high [C~I] abundance. Due to the spatially extended nature of the winds, using a large beam ($\simeq0.4$" for disks in nearby star-forming regions) will be helpful regardless of the tracer used.