The evolution of protoplanetary disc radii and disc masses in star-forming regions

TL;DR

This study combines star formation simulations with disc evolution models to understand how protoplanetary disc sizes and masses change in different environments, highlighting the importance of initial conditions and external photoevaporation effects.

Contribution

It provides a coupled simulation and analysis framework to study disc evolution, revealing initial disc sizes and environmental densities consistent with observations.

Findings

Initial disc radii are around 100au to match observations.

Observed disc radii in Orion suggest moderate initial stellar densities.

External photoevaporation impacts disc size evolution differently across regions.

Abstract

Protoplanetary discs are crucial to understanding how planets form and evolve, but these objects are subject to the vagaries of the birth environments of their host stars. In particular, photoionising radiation from massive stars has been shown to be an effective agent in disrupting protoplanetary discs. External photoevaporation leads to the inward evolution of the radii of discs, whereas the internal viscous evolution of the disc causes the radii to evolve outwards. We couple N-body simulations of star-forming regions with a post-processing analysis of disc evolution to determine how the radius and mass distributions of protoplanetary discs evolve in young star-forming regions. To be consistent with observations, we find that the initial disc radii must be of order 100au, even though these discs are readily destroyed by photoevaporation from massive stars. Furthermore, the observed disc radii distribution in the Orion Nebula Cluster is more consistent with moderate initial stellar densities (100M$_\odot$ pc$^{-3}$), in tension with dynamical models that posit much higher inital densities for the ONC. Furthermore, we cannot reproduce the observed disc radius distribution in the Lupus star-forming region if its discs are subject to external photoevaporation. A more detailed comparison is not possible due to the well-documented uncertainties in determining the ages of pre-main sequence (disc-hosting) stars.