Models and Observational Predictions of Dust Traps in Protoplanetary Discs

TL;DR

This paper models dust trapping in protoplanetary discs, showing how parameters like pressure bumps, fragmentation velocity, and viscosity influence observable features and dust retention, with implications for planet formation.

Contribution

It provides detailed models linking dust evolution parameters to observable disc structures, emphasizing degeneracies and the importance of multi-wavelength observations.

Findings

Pressure bumps significantly enhance dust retention.

Low fragmentation velocities favor long-term dust retention.

Disc viscosity shapes observable features like cavities and rings.

Abstract

This manuscript investigates the impact of key dust evolution parameters on dust retention and trapping in protoplanetary discs. Using models with and without pressure bumps, combined with radiative transfer simulations, images of the dust continuum emission at (sub-)millimeter wavelengths, their fluxes and observed disc sizes are presented. For discs without pressure bumps (smooth discs), significant dust mass can only be retained over Myr timescales when dust fragmentation velocities are low (1m/s) and with viscosity values of $\alpha=10^{-3}$. For such a combination of fragmentation velocity and viscosity, the synthetic images show a bright inner emission follow by a shallow emission with potential gaps if they are present in the gas profile as well. At higher fragmentation velocities (5-10m/s), most dust is lost due to radial drift at million-year timescales unless pressure traps are present, in which case dust masses can increase by orders of magnitude and structures are observed in synthetic images. The viscosity parameter strongly shapes observable features, with low $\alpha$ producing sharper, potentially asymmetric inner wall cavities in inclined discs due to optically thick emission. High $\alpha$ favors the appearance of shoulders around the predominant rings that dust trapping produces. However, distinguishing between different fragmentation velocities observationally remains challenging. The inferred dust disc sizes from synthetic observations do not always correspond directly to dust model sizes or to the location of pressure bumps. Finally, we discuss implications for pebble fluxes and the delivery of volatiles to the inner disc. These results emphasize the strong degeneracies among dust evolution parameters and highlight the need for multi-wavelength, high-resolution observations to disentangle the processes shaping the formation of planets in protoplanetary discs.