How the gradient of $M_{\rm d}$ versus UV field strength yields insights into the ages of protoplanetary disc populations

TL;DR

This study uses models to analyze how the relationship between dust disc mass and UV radiation strength changes over time, revealing insights into the ages and evolution of protoplanetary disc populations.

Contribution

It introduces a model-based analysis of the gradient of disc mass versus UV field strength, linking it to disc age, stellar mass, and angular momentum transport mechanisms.

Findings

The slope flattens as disc populations age.

More massive stars have steeper gradients.

Stronger viscosity or MHD winds affect the gradient significantly.

Abstract

FUV radiation from massive stars launch photoevaporative winds from the outer regions of protoplanetary discs around other stars, removing gas and dust. Observations have identified a relation between the median dust disc mass and the external UV field strength. Here we use disc evolutionary models to explore how this relation evolves over time, and with respect to other stellar and disc properties. We find that the slope for the relationship $\lambda_{\rm UV}$ flattens over time as populations age, possibly explaining the differences seen between the L1641-N and L1641-S clusters in Orion A. We determine that $\lambda_{\rm UV}$ depends on the stellar mass where more massive stars exhibit steeper gradients than their lesser counterparts, in agreement with the differences seen between Herbig and T Tauri stars. Additionally, the strength of the mechanism for angular momentum transport, either viscosity or MHD disc winds, is found to significantly affect $\lambda_{\rm UV}$ with stronger $\alpha$ values reducing $\lambda_{\rm UV}$ due to more material accreting on to the central stars in weaker UV environments. Estimates of $\lambda_{\rm UV}$ from observations of L1641 place preliminary constraints on $\alpha$ to be between $10^{-3.5}$--$10^{-2.5}$, consistent with literature estimates. Further observations in different regions and better classifications of stellar masses will allow us to place stringent constraints on disc evolution properties, improving our understanding of how protoplanetary discs evolve.