A millimeter-multiwavelength continuum study of VLA 1623 West

TL;DR

This study uses high-resolution ALMA observations to model VLA 1623 West, revealing it as a flared, optically thick protostellar disk with implications for early planet formation.

Contribution

It provides the first detailed geometric modeling of VLA 1623 West, suggesting it is a flared, young protostellar disk with unsettled dust, advancing understanding of early disk evolution.

Findings

VLA 1623W is best modeled as a highly inclined, optically thick disk.

Residuals indicate the disk is flared, especially in the outer regions.

The disk's dust settling is incomplete, affecting planet formation theories.

Abstract

VLA 1623 West is an ambiguous source that has been described as a shocked cloudlet as well as a protostellar disk. We use deep ALMA 1.3 and 0.87 millimeter observations to constrain its shape and structure to determine its origins better. We use a series of geometric models to fit the uv visibilities at both wavelengths with GALARIO. Although the Real visibilities show structures similar to what has been identified as gaps and rings in protoplanetary disks, we find that a modified Flat-Topped Gaussian at high inclination provides the best fit to the observations. This fit agrees well with expectations for an optically thick, highly inclined disk. Nevertheless, we find that the geometric models consistently yield positive residuals at the four corners of the disk at both wavelengths. We interpret these residuals as evidence that the disk is flared in the millimeter dust. We use a simple toy model for an edge-on flared disk and find that the residuals best match a disk with flaring that is mainly restricted to the outer disk at $R \gtrsim 30$ au. Thus, VLA 1623W may represent a young protostellar disk where the large dust grains have not yet had enough time to settle into the mid-plane. This result may have implications for how disk evolution and vertical dust settling impact the initial conditions leading to planet formation.