Final Masses of Giant Planets. III. Effect of Photoevaporation and a New Planetary Migration Model

We herein develop a new simple model for giant planet formation that predicts the final mass of a giant planet born in a given disk by adding the disk mass loss due to photoevaporation and a new type II migration formula to our previous model. The proposed model provides some interesting results. First, it gives universal evolution tracks in the diagram of planetary mass and orbital radius, which clarifies how giant planets migrate at growth in the runaway gas accretion stage. Giant planets with a few Jupiter masses or less suffer only a slight radial migration in the runaway gas accretion stage. Second, the final mass of giant planets is approximately given as a function of only three parameters: The initial disk mass at the starting time of runaway gas accretion onto the planet, the mass-loss rate due to photoevaporation, and the starting time. On the other hand, the final planet mass is almost independent of the disk radius, viscosity, and planetary orbital radius. The obtained final planet mass is ≲10% of the initial disk mass. Third, the proposed model successfully explains properties in the mass distribution of giant exoplanets with the mass distribution of observed protoplanetary disks for a reasonable range of the mass-loss rate due to photoevaporation.