The Resolved Spatial Distribution of Solids in Protoplanetary Disks

Abstract

Observations of protoplanetary disks provide key constraints on theories of planet formation. The fundamental challenge for planet formation theory is the timescale for the formation of planetesimals. Theory predicts that solids rapidly migrate toward the star before they have the time to grow into planetesimals. Since dust particles emit thermally out to microwave wavelengths and the shape of the spectrum varies with particle size, microwave observations of protoplanetary disks can trace the growth and migration of solids. In this dissertation, I use resolved continuum measurements at multiple wavelengths, from sub-millimeter to centimeter, to demonstrate radial variations in the spectrum of the protoplanetary disk around UZ Tau E. My analysis is based on a metric for disk size that I define as the radius within which a fraction of the total flux is enclosed. This effective disk size increases with observing frequency, suggesting that the largest particles are closest to the star. I apply the same size metric to a survey of fifty protoplanetary disks, observed at 340 GHz with the Submillimeter Array. Motivated by smaller surveys that hinted that disk size increases with luminosity, I confirm and extend those results to fainter sources. Both this size-luminosity relationship and the UZ Tau E size-frequency relationship qualitatively agree with theoretical models of dust evolution. However, the age of the observed systems are in tension with the model timescales. The presence of substructure in the disk could concentrate dust particles and alleviate this tension, but substructure is not included in the models. Substructure has been observed in several disks with high resolution ALMA measurements. In the final chapter of this dissertation, I explore a model-agnostic method for characterizing such substructure in disk surface brightness profiles. By quantitatively characterizing disk substructure, this methodology can help inform dust evolution models, with the ultimate goal of slowing dust migration.