The ALMA survey to Resolve exoKuiper belt Substructures (ARKS)

Abstract

Context . The dust observed in debris disks is the result of a collisional cascade initiated from approximately kilometer-sized parent bodies. Using near-infrared to submillimeter 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 survey to Resolve exoKuiper belt Substructures (ARKS) program allowed for a detailed comparison with near-infrared scattered light observations, at an unprecedented resolution. Aims . The comparison between the two wavelength regimes reveals that for most gas-bearing debris disks, the distribution of small dust grains peaks outside the distribution of large dust grains. In this paper, we investigate whether gas-dust interactions can explain such radial offsets. Methods . We performed numerical simulations that account for the effects of radiation pressure, gas drag, and collisions, and computed surface brightness profiles at several wavelengths to assess which parameters drive these radial offsets. We explored several families of models, varying the gas mass, disk optical depth, dust size distribution, and radiation pressure strength. Results . We find that while higher 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 micron-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 submillimeter images, and we discuss the formation of secondary rings at near-infrared wavelengths. Conclusions . The angular resolution achieved by the ARKS program has opened a new avenue for studying the dynamics of dust particles in debris disks, revealing unexpected differences between the appearance of the disks scattered light and thermal emission. We show that gas-dust interactions can explain the observed radial offsets and provide pointers as to which parameters have the most significant impact.