Hints on the origins of particle traps in protoplanetary disks given by the M_dust - M_⋆ relation

Abstract

Context. Demographic surveys of protoplanetary disks, carried out mainly with the Atacama Large Millimeter/submillimete Array, have provided access to a large range of disk dust masses (M_dust) around stars with different stellar types and in different star-forming regions. These surveys found a power-law relation between M_dust and M_⋆ that steepens in time, but which is also flatter for transition disks (TDs).
Aims: We aim to study the effect of dust evolution in the M_dust-M_⋆ relation. In particular, we are interested in investigating the effect of particle traps on this relation.
Methods: We performed dust evolution models, which included perturbations to the gas surface density with different amplitudes to investigate the effect of particle trapping on the M_dust-M_⋆ relation. These perturbations were aimed at mimicking pressure bumps that originated from planets. We focused on the effect caused by different stellar and disk masses based on exoplanet statistics that demonstrate a dependence of planet mass on stellar mass and metallicity.
Results: Models of dust evolution can reproduce the observed M_dust-M_⋆ relation in different star-forming regions when strong pressure bumps are included and when the disk mass scales with stellar mass (case of M_disk = 0.05 M_⋆ in our models). This result arises from dust trapping and dust growth beyond centimeter-sized grains inside pressure bumps. However, the flatter relation of M_dust - M_⋆ for TDs and disks with substructures cannot be reproduced by the models unless the formation of boulders is inhibited inside pressure bumps.
Conclusions: In the context of pressure bumps originating from planets, our results agree with current exoplanet statistics on giant planet occurrence increasing with stellar mass, but we cannot draw a conclusion about the type of planets needed in the case of low-mass stars. This is attributed to the fact that for M_⋆ < 1 M_⊙, the observed M_dust obtained from models is very low due to the efficient growth of dust particles beyond centimeter-sizes inside pressure bumps.