Photoevaporation Can Reproduce Extended $\mathrm{H_2}$ Emission from Protoplanetary Disks Imaged by JWST MIRI

TL;DR

This study develops a radiation hydrodynamics model of photoevaporative H2 winds in protoplanetary disks, successfully reproducing observed JWST H2 emission morphologies and fluxes, thus supporting photoevaporation as a key disk dispersal mechanism.

Contribution

First tailored model of photoevaporative H2 winds for direct comparison with JWST observations, combining simulations with chemistry and radiative transfer.

Findings

Reproduces observed X-shaped H2 wind morphology with realistic extents and angles.

Predicted line fluxes are close but slightly lower than observations.

Supports photoevaporation as a plausible explanation for observed H2 features.

Abstract

Understanding dispersal of protoplanetary disks remains a central challenge in planet formation theory. Disk winds, driven by magnetohydrodynamics (MHD) and/or photoevaporation, are now recognized as primary agents of dispersal. With the advent of James Webb Space Telescope (JWST), spatially resolved imaging of these winds, particularly in H2 pure rotational lines, has become possible, revealing X-shaped morphologies and integrated fluxes of $\sim 10^{-16}$-$10^{-15}{\rm \,erg\,s^{-1}\,cm^{-2}}$. However, the lack of theoretical models suitable for direct comparison has limited interpretation of these features. To address this, we present the first model of photoevaporative \ce{H2} winds tailored for direct comparison with JWST observations. Using radiation hydrodynamics simulations coupled with chemistry, we derive steady-state wind structures and post-process them to compute H2 level populations and line radiative transfer, including collisional excitation and spontaneous decay. Our synthetic images reproduce the observed X-shaped morphology with radial extents of $\gtrsim 50$-$300{\rm \,au}$ and semi-opening angles of $\sim 37^\circ$-$50^\circ$, matching observations of Tau 042021 and SY Cha. While the predicted line fluxes are somewhat lower than the observed values. These results suggest that photoevaporation is a viable mechanism for reproducing key features of observed H2 winds, including morphology and fluxes, though conclusive identification of the wind origin requires source-specific modeling. This challenges the reliance on geometrical structures alone to distinguish between MHD winds and photoevaporation. Based on our findings, we also discuss alternative diagnostics of photoevaporative winds. This work provides a critical first step toward interpreting spatially resolved H2 winds and motivates future modeling efforts.