External Photoevaporation of Protoplanetary Disks: Does Location Matter?

Abstract

Many theoretical studies have shown that external photoevaporation from massive stars can severely truncate, or destroy altogether, the gaseous protoplanetary disks around young stars. In tandem, several observational studies report a correlation between the mass of a protoplanetary disk and its distance to massive ionizing stars in star-forming regions, and cite external photoevaporation by the massive stars as the origin of this correlation. We present N-body simulations of the dynamical evolution of star-forming regions and determine the mass loss in protoplanetary disks from external photoevaporation due to far-ultraviolet and extreme-ultraviolet radiation from massive stars. We find that projection effects can be significant, in that low-mass disk-hosting stars that appear close to the ionizing sources may be fore- or background stars in the star-forming region. We find very little evidence in our simulations for a trend in increasing disk mass with increasing distance from the massive star(s), even when projection effects are ignored. Furthermore, the dynamical evolution of these young star-forming regions moves stars whose disks have been photoevaporated to far-flung locations, away from the ionizing stars, and we suggest that any correlation between disk mass and distance from the ionizing star is either coincidental, or due to some process other than external photoevaporation.

Gaia EDR3 comparative study of protoplanetary disk fractions in young stellar clusters

“…Indeed, the presence of massive stars or stellar interactions in the densest and more massive clusters may lead to a fast disappearance of the outer disk probed at submillimeter and millimeter wavelengths (e.g., Anderson et al 2013;Ansdell et al 2017;Vincke & Pfalzner 2018;van Terwisga et al 2019). The eventual influence of such environmental effects is the subject of ongoing debate (see, e.g., the discussion in Parker et al 2021, and references therein), but it does not seem to affect the bulk of the disks probed at shorter IR wavelengths (e.g., Richert et al 2015). Such a possible difference with the outer disk dispersal depending on the environment cannot be analyzed based on the JHK photometry used in this work, which we remark again that only refers to inner dust disks.…”

“…The eventual influence of such environmental effects is the subject of ongoing debate (see e.g. the discussion in Parker et al 2021, and references therein), but it does not seem to affect the bulk of the disks probed at shorter IR wavelengths (e.g. Richert et al 2015).…”

The external photoevaporation of planet-forming discs

“…The three dimensional geometry (projection effects) and dynamical mixing in stellar aggregates may also hide correlations between historic FUV exposure and present day disc properties (e.g. Parker et al, 2021). Even empirically quantifying the luminosity and spectral type of neighbour OB stars can be challenging.…”

“…One explanation is that, given the older age (∼ 5 Myr) of the region, the discs may have all reached a similar state of depletion, with spatial correlations washed out by dynamical mixing (e.g. Parker et al, 2021). Meanwhile, in a survey of non-irradiated discs, van Terwisga et al (2022) demonstrated that discs in SFRs of similar ages appear to have similar dust masses, suggesting that any observed depletion in higher mass SFRs is probably the result of an environmental effect.…”

“…Many studies have performed N-body simulations of SFRs to track the exposure of star-disc systems, either with aim of quantifying general trends (Holden et al, 2011;Nicholson et al, 2019;Concha-Ramírez et al, 2019;Parker et al, 2021) or modelling specific regions (Scally and Clarke, 2001;Winter et al, 2019bWinter et al, , 2020a. These studies generally adopt the FUV driven mass loss rates given by the FRIED grid (Haworth et al, 2018a) with an external flux computed directly from N-body simulations.…”