On the diversity of asymmetries in gapped protoplanetary disks

TL;DR

This study analyzes 16 protoplanetary disks with dust cavities, revealing how asymmetries relate to gas density and potential planetary companions, and discusses the origins of these asymmetries and their implications for planet formation.

Contribution

It provides a comprehensive comparison of dust and gas structures in disks, constrains companion masses, and links spiral features to star luminosity and disk properties, advancing understanding of disk asymmetries.

Findings

Asymmetries correlate with higher Stokes numbers or low gas density.

Gas gap radii suggest companions are in brown dwarf or super-Jovian mass regimes.

Spiral arms are mainly detected around high luminosity stars with wide gaps.

Abstract

Protoplanetary disks with large inner dust cavities are thought to host massive planetary or substellar companions. These disks show asymmetries and rings in the millimeter continuum, caused by dust trapping in pressure bumps, and potentially vortices or horseshoes. The origin of the asymmetries and their diversity remains unclear. We present a comprehensive study of 16 disks for which the gas surface density profile has been constrained by CO isotopologue data. We compare the azimuthal extents of the dust continuum profiles with the local gas surface density in each disk, and find that the asymmetries correspond to higher Stokes numbers or low gas surface density. We discuss which asymmetric structures can be explained by a horseshoe, a vortex or spiral density waves. Second, we reassess the gas gap radii from the $^{13}$CO maps, which are about a factor 2 smaller than the dust ring radii, suggesting that companions in these disks are in the brown dwarf mass regime ($\sim 15-50 M_{\rm Jup}$) or in the Super-Jovian mass regime ($\sim 3-15 M_{\rm Jup}$) on eccentric orbits. This is consistent with the estimates from contrast curves on companion mass limits. These curves rule out (sub)stellar companions ($q>$0.05) for the majority of the sample at the gap location, but it remains possible at even smaller radii. Third, we find that spiral arms in scattered light images are primarily detected around high luminosity stars with disks with wide gaps, which can be understood by the dependence of the spiral arm pitch angle on disk temperature and companion mass.