Anisotropic Infall and Substructure formation in Embedded Disks

TL;DR

This paper investigates how anisotropic infall of material onto protostellar disks causes substructures like rings and spirals, influencing dust dynamics and potentially explaining observed features in young stellar objects.

Contribution

It provides a parameter study of anisotropic infall effects on disk stability, vortex formation, and dust trapping, linking accretion flow properties to observable disk substructures.

Findings

Anisotropic infall triggers Rossby wave instability and vortex formation.

Vortices create pressure bumps that trap dust and influence disk morphology.

Models can produce millimeter rings and compact dust disks consistent with observations.

Abstract

The filamentary nature of accretion streams found around embedded sources suggest that protostellar disks experience heterogenous infall from the star-forming environment, consistent with the accretion behavior onto star-forming cores in top-down star-cluster formation simulations. This may produce disk substructures in the form of rings, gaps, and spirals continuing to be identified by high-resolution imaging surveys in both embedded Class 0/I and later Class II sources. We present a parameter study of anisotropic infall, informed by the properties of accretion flows onto protostellar cores in numerical simulations, and varying the relative specific angular momentum of incoming flows as well as their flow geometry. Our results show that anisotropic infall perturbs the disk and readily launches the Rossby wave instability (RWI). It forms vortices at the inner and outer edge of the infall zone where material is deposited. These vortices drive spiral waves and angular momentum transport, with some models able to drive stresses corresponding to a viscosity parameter on the order of $\alpha \sim 10^{-2}$. The resulting azimuthal shear forms robust pressure bumps that act as barriers to radial drift of dust grains, as demonstrated by post-processing calculations of drift-dominated dust evolution. We discuss how a self-consistent model of anisotropic infall can account for the formation of millimeter rings in the outer disk as well as producing compact dust disks, consistent with observations of embedded sources.