Axisymmetric Modeling of DSHARP Dusty Disks: Asymmetric Structures and Inner-Disk Dispersal

TL;DR

The paper tackles the challenge of identifying embedded planets in protoplanetary disks by separating faint non-axisymmetric signals from the dominant axisymmetric dust emission using axisymmetric, geometrically-thin-disk modeling. It employs a Hankel-transform–based reconstruction with a Gaussian-process prior to recover high-resolution radial brightness profiles and geometric parameters from ALMA DSHARP data, producing residual images that reveal non-axisymmetric structures. Key findings include no compelling circumplanetary emission detections, a possible one-armed spiral in Elias 27, and spirals in Elias 27, IM Lup, and WaOph 6, along with residuals tied to the vertical thickness of dust layers in several disks; inner-disk brightness temperatures decline with stellar age on a timescale of roughly 3 Myr, consistent with pressure bumps retaining outer dust and promoting inner-disk dispersal. The results suggest a universal disk dispersal timescale at millimeter wavelengths, which may constrain the timing of planet formation, including habitable planets.

Abstract

High-resolution observations of Class II protoplanetary disks frequently reveal annular structures that may indicate the presence of embedded planets. In this study, we model brightness profiles and geometries for 16 dusty disks in the DSHARP observations to identify asymmetric substructures, including possible planet-induced signatures. We find no compelling evidence for circumplanetary emission in these systems. We identify a possible one-armed spiral in Elias 27; while previous studies report an $m=2$ spiral, the morphology of the newly identified spiral agrees with a spiral for a possible protoplanet. Although non-detection of circumplanetary emission is consistent with low expected luminosities, the absence of additional dust spirals except for Elias 27 may constrain properties of potential embedded planets given their theoretical detectability. The analyses further suggest that spiral amplitudes and phases correlated with gap and ring locations in WaOph 6 and IM Lup, appearing as deflections of spirals in images. Five disks exhibit strong residual asymmetries attributable to the vertical extent of their dust layers. We find that the brightness temperature of inner disks ($1$-$5$ au) declines with stellar age on a $\sim 3$ Myr timescale, while the total flux shows no clear decreasing trend. This trend is consistent with the presence of pressure bumps that retain large dust grains at outer radii, while allowing the inner disks to disperse. The universality of disk dispersal timescale at millimeter wavelengths, observed in both the extended DSHARP disks and the compact disks from previous demographic surveys, may constrain timing of planet formation, including habitable planets.