The ALMA survey to Resolve exoKuiper belt Substructures (ARKS) XI: Gas-dust interactions and radial offsets between micron and millimetre-sized grains

TL;DR

This study uses high-resolution ALMA and near-infrared observations to analyze gas-dust interactions in debris disks, revealing how these interactions cause radial offsets between different-sized dust grains and how various parameters influence these offsets.

Contribution

The paper demonstrates through simulations that gas-dust interactions explain observed radial offsets and identifies key parameters affecting dust distribution in debris disks.

Findings

Gas mass increases outward radial drift efficiency.

Radial offset depends on disk optical depth and collisional lifetime.

Increasing micron-sized dust enhances radial offsets.

Abstract

The dust observed in debris disks is the result of a collisional cascade initiated from $\sim$ km-sized parent bodies. Using near-infrared to sub-millimeter observations, we can probe particle sizes spanning 2-3 orders of magnitude, and with sufficient angular resolution we can follow the dynamics of these dust particles. Observations taken as part of the ALMA ARKS program allowed for a detailed comparison with near-infrared scattered light observations, at unprecedented resolution. The comparison between the two wavelength regimes reveals that for most gas-bearing debris disks, the distribution of small dust grains peaks outward of the distribution of large dust grains. In this paper we investigate whether gas-dust interactions can explain such radial offsets. We perform numerical simulations and compute surface brightness profiles at several wavelengths to assess which parameters drive these radial offsets. We find that while larger gas masses lead to more efficient outward radial drift, the resulting radial offset strongly depends on the optical depth of the disk, as the drift efficiency directly competes with the particles' collisional lifetime. We also find that increasing the relative number of $\mu$m-sized dust grains usually yields a larger radial offset between scattered light and millimeter observations. Finally, we show that mid-infrared observations can complement near-infrared and sub-millimeter images, and we discuss the formation of secondary rings at near-infrared wavelengths. The angular resolution achieved by the ARKS program has opened a new avenue to study the dynamics of dust particles in debris disks, revealing unexpected differences between the appearance of the disks scattered light and thermal emission. We showed that gas-dust interactions can explain the observed radial offsets and provide pointers as to which parameters have the most significant impact.