A Steeper than Linear Disk Mass-Stellar Mass Scaling Relation

TL;DR

This study reveals that disk mass scales with stellar mass more steeply than linear in young star-forming regions, with implications for planet formation models and grain growth processes.

Contribution

The paper provides the first comprehensive analysis of the dust mass-stellar mass relation across multiple regions, showing a steeper than linear scaling in young disks.

Findings

Disk mass-stellar mass relation is steeper than linear with index 1.3-1.9.

Similar relations are found in 1-3 Myr regions, but steeper in 10 Myr-old Upper Sco.

Grain growth models support a fragmentation-limited regime in disks.

Abstract

The disk mass is among the most important input parameter for every planet formation model to determine the number and masses of the planets that can form. We present an ALMA 887micron survey of the disk population around objects from 2 to 0.03Msun in the nearby 2Myr-old Chamaeleon I star-forming region. We detect thermal dust emission from 66 out of 93 disks, spatially resolve 34 of them, and identify two disks with large dust cavities of about 45AU in radius. Assuming isothermal and optically thin emission, we convert the 887micron flux densities into dust disk masses, hereafter Mdust. We find that the Mdust-Mstar relation is steeper than linear with power law indices 1.3-1.9, where the range reflects two extremes of the possible relation between the average dust temperature and stellar luminosity. By re-analyzing all millimeter data available for nearby regions in a self-consistent way, we show that the 1-3 Myr-old regions of Taurus, Lupus, and Chamaeleon I share the same Mdust-Mstar relation, while the 10Myr-old Upper Sco association has a steeper relation. Theoretical models of grain growth, drift, and fragmentation reproduce this trend and suggest that disks are in the fragmentation-limited regime. In this regime millimeter grains will be located closer in around lower-mass stars, a prediction that can be tested with deeper and higher spatial resolution ALMA observations.