On the origin of compressive turbulence in protoclumps in high redshift disks

Understand

The giant, star forming clumps in gas-rich, high redshift disks are commonly assumed to form due to gravitational instabilities, in which protoclumps have a Toomre-$Q$ parameter less than unity.

• However, some cosmological simulations show that clumps can form in regions where $Q\gg1$.
• In these simulations, there is an excess of compressive modes of turbulence that lead to gravitational collapse of regions that were not supposed to gravitationally collapse, according to linear theory.
• In contrast, sites of clump formation in isolated simulations do not show this excess, hinting that the origin may be external.