Kinematic Morphology of Large-scale Structure: Evolution from Potential to Rotational Flow

Understand

As an alternative way of describing the cosmological velocity field, we discuss the evolution of rotational invariants constructed from the velocity gradient tensor.

• Compared with the traditional divergence-vorticity decomposition, these invariants, defined as coefficients of characteristic equation of the velocity gradient tensor, enable a complete classification of all possible flow patterns in the dark-matter comoving frame, including both potential and vortical flows.
• We show that this tool, first introduced in turbulence two decades ago, proves to be very useful in understanding the evolution of the cosmic web structure, and in classifying its morphology.
• Before shell-crossing, different categories of potential flow are highly associated with cosmic web structure, because of the coherent evolution of density and velocity.