Constraints from Dust Mass and Mass Accretion Rate Measurements on Angular Momentum Transport in Protoplanetary Disks

TL;DR

This study examines the relationship between dust mass and accretion rate in protoplanetary disks to understand angular momentum transport, suggesting either physical process effects or initial conditions as explanations for observed scatter.

Contribution

It provides new insights into the correlation between dust mass and accretion rate, and explores two scenarios explaining the observed scatter, informing models of disk evolution and angular momentum transport.

Findings

Dust mass and accretion rate are correlated with a slope close to linear.

Standard alpha viscosity models over-predict the correlation strength.

Two scenarios: physical processes cause scatter or disks are unevolved due to low viscosity or large initial size.

Abstract

We investigate the relation between disk mass and mass accretion rate to constrain the mechanism of angular momentum transport in protoplanetary disks. Dust mass and mass accretion rate in Chamaeleon I are correlated with a slope close to linear, similar to the one recently identified in Lupus. We investigate the effect of stellar mass and find that the intrinsic scatter around the best-fit Mdust-Mstar and Macc-Mstar relations is uncorrelated. Disks with a constant alpha viscosity can fit the observed relations between dust mass, mass accretion rate, and stellar mass, but over-predict the strength of the correlation between disk mass and mass accretion rate when using standard initial conditions. We find two possible solutions. 1) The observed scatter in Mdust and Macc is not primoridal, but arises from additional physical processes or uncertainties in estimating the disk gas mass. Most likely grain growth and radial drift affect the observable dust mass, while variability on large time scales affects the mass accretion rates. 2) The observed scatter is primordial, but disks have not evolved substantially at the age of Lupus and Chamaeleon I due to a low viscosity or a large initial disk radius. More accurate estimates of the disk mass and gas disk sizes in a large sample of protoplanetary disks, either through direct observations of the gas or spatially resolved multi-wavelength observations of the dust with ALMA, are needed to discriminate between both scenarios or to constrain alternative angular momentum transport mechanisms such as MHD disk winds.