Photochemical-dynamical models of externally FUV irradiated protoplanetary discs

TL;DR

This paper presents the first full radiation hydrodynamic simulations of protoplanetary discs irradiated by FUV radiation, validating semi-analytic models and providing new insights into disc mass loss and flow composition.

Contribution

It introduces a novel numerical method for modeling externally irradiated protoplanetary discs, validating semi-analytic models, and exploring flow composition and diagnostics.

Findings

Excellent agreement with semi-analytic models for flow profile and mass loss rate.

Validated the critical radius concept in disc photoevaporation.

Provided preliminary diagnostics for future observational studies.

Abstract

There is growing theoretical and observational evidence that protoplanetary disc evolution may be significantly affected by the canonical levels of far ultraviolet (FUV) radiation found in a star forming environment, leading to substantial stripping of material from the disc outer edge even in the absence of nearby massive stars. In this paper we perform the first full radiation hydrodynamic simulations of the flow from the outer rim of protoplanetary discs externally irradiated by such intermediate strength FUV fields, including direct modelling of the photon dominated region (PDR) which is required to accurately compute the thermal properties. We find excellent agreement between our models and the semi-analytic models of Facchini et al. (2016) for the profile of the flow itself, as well as the mass loss rate and location of their "critical radius". This both validates their results (which differed significantly from prior semi-analytic estimates) and our new numerical method, the latter of which can now be applied to elements of the problem that the semi--analytic approaches are incapable of modelling. We also obtain the composition of the flow, but given the simple geometry of our models we can only hint at some diagnostics for future observations of externally irradiated discs at this stage. We also discuss the potential for these models as benchmarks for future photochemical-dynamical codes.