2021MNRAS.506.5969B

Substructures are ubiquitous in high resolution (sub-)millimeter continuum observations of circumstellar discs. They are possibly caused by forming planets embedded in their disc. To investigate the relation between observed substructures and young planets, we perform novel 3D two-fluid (gas+1-mm-dust) hydrodynamic simulations of circumstellar discs with embedded planets (Neptune-, Saturn-, Jupiter-, 5 Jupiter-mass) at different orbital distances from the star (5.2 AU, 30 AU, 50 AU). We turn these simulations into synthetic (sub-)millimeter ALMA images. We find that all but the Neptune-mass planet open annular gaps in both the gas and the dust component of the disc. We find that the temporal evolution of the dust density distribution is distinctly different from the gas'. For example, the planets cause significant vertical stirring of the dust in the circumstellar disc which opposes the vertical settling. This creates a thicker dust disc than discs without a planet. We find that this effect greatly influences the dust masses derived from the synthetic ALMA images. Comparing the dust disc masses in the 3D simulations to the disc masses derived from the 2D ALMA synthetic images using the optically thin approximation, we find the former to be a factor of a few (up to 10) larger, pointing to the conclusion that real discs are significantly more massive than previously thought based on ALMA continuum images. Finally, we analyse the synthetic ALMA images and provide an empirical relationship between the planet mass and the width of the gap in the ALMA images, including the effects of the beam size.