The evolution of the flux-size relationship in protoplanetary discs by viscous evolution and radial pebble drift

TL;DR

This study models the evolution of fluxes, radii, and dust masses in protoplanetary discs, highlighting how angular momentum and heating efficiency influence observable properties and aligning with observations of young star clusters.

Contribution

It introduces a comprehensive model combining viscous disc evolution and dust dynamics, explaining observed fluxes and radii across different disc classes.

Findings

Best matches to observations with 40 au initial angular momentum and inefficient viscous heating.

Discs transition from optically thick to thin at mm wavelengths after 0.5 Myr.

Model reproduces observed dust mass evolution in young star clusters.

Abstract

In this paper we study the evolution of radiative fluxes, flux radii and observable dust masses in protoplanetary discs, in order to understand how these depend on the angular momentum budget and on the assumed heat sources. We use a model that includes the formation and viscous evolution of protoplanetary gas discs, together with the growth and radial drift of the dust component. We find that we are best able to match the observed fluxes and radii of class 0/I discs when we assume (i) an initial total angular momentum budget corresponding to a centrifugal radius of 40 au around solar-like stars, and (ii) inefficient viscous heating. Fluxes and radii of class II discs appear consistent with disc models with angular momentum budgets equivalent to centrifugal radii of both 40 au or 10 au for solar like stars, and with models where viscous heating occurs at either full efficiency or at reduced efficiency. During the first 0.5 Myr of their evolution discs are generally optically thick at a wavelength of 1.3 mm. However, after this discs are optically thin at mm-wavelengths, supporting standard means of dust mass estimates. Using a disc population synthesis model, we then show that the evolution of the cumulative evolution of the observable dust masses agrees well with that observed in young star forming clusters of different ages.