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Abstract

Early protoplanetary disks are cool and massive and thus subject to gravitational instabilites and fragmentation of the disk into dense clumps of gas. These fragments are massive enough to become gas giant planets and brown dwarfs in the distant regions of the disks beyond 50 au where traditional planet formation scenarios have trouble creating planetary cores fast enough to explain directly observed planets. I used high-resolution three-dimensional hydrodynamic simulations to model the collapse of self-gravitating disks to constrain the formation location of these fragments and characterize their initial gas and particle masses to compare to directly observed planets and brown dwarfs. I find the traditional cooling criterion, which constrains the formation location to the outer disk, is converged in these simulations and overall masses are consistent with massive gas giants bordering on brown dwarfs. The concentration of solid material in these fragments leads to an increase of the overall metallicity of the fragment and a solid core several tens of Earth masses. To model fragmentation with full disk simulations, I have also implemented a multigrid self-gravity solver in the PLUTO code which uses adaptive mesh refinement to resolve both the disk and fragments.