Constraints on the properties of PDS70c from the continuum emission of evolving dust in the circumplanetary disk

Yuhito Shibaike

The dust continuum emission from the circumplanetary disk (CPD) of a gas accreting young planet, PDS70c, has been observed by ALMA Band 7 (855μm) as the first and only detection of CPDs. Observations of CPDs can provide essential constraints on the gas planets and their gas accretion processes. The intensity of dust emission from CPDs depends on the radial distribution of the size and surface density of dust in the disks. In the previous works, however, the evolution of dust in the CPD of PDS70c has not been considered; only the total mass of dust was estimated with the several fixed sizes of dust. We built a more detailed 1D gas accretion CPD model and calculated the collisional growth and radial drift of dust in the disk. We then estimated the continuum emission from the evolving dust considering its size-frequency distribution. We carried out Monte Carlo simulations with various parameter sets and succeeded in reproducing the observation. We found that the observed peak intensity, 86μJy/beam, can be reproduced when the gas accretion rate is ~0.1 MJ/Myr, and the strength of turbulence of the CPD is α~10^(-5). The gas accretion rate has also been estimated from the observation of Hα and Hβ line emission, and the high gas accretion rate of our result is consistent with that estimate. The turbulence could also be weak, because magnetorotational instability is not likely to occur in CPDs. We also found that the intensity of dust emission does not depend on the planet mass. In addition, we discuss the constraints on the properties of PDS70b, where the dust emission from its CPD has not been detected.