Extremely flat protoplanetary disks: a favorable environment for planetary growth

To form giant planets in protoplanetary disk lifetime, small micron sized particles must grow rapidly to larger grains. A full understanding of that process requires a detailed characterization of the radial and vertical structure of the gas-rich disks associated with young pre-main sequence stars. Disks observed edge-on are of particular interest as they provide a unique point of view to unambiguously disentangle their vertical and radial dimensions. Here we present ALMA extremely high angular resolution imaging (up to a few AU scales) of one edge-on disk in the nearby Ophiuchus star-forming region. The modeling of the millimeter continuum image and a previously published scattered light image with radiative transfer enables a robust comparison of the spatial distribution of millimeter-sized grains and micron-sized dust grains in this disk. We find that the large dust grains are constrained to a remarkably flat subdisk as a consequence of dust settling. We place stringent constraints on the thickness of this subdisk in this system, on vertical settling efficiency, and on the potential for wide-orbit planet formation in this disk.