Speaker
Description
Cosmic velocities can be decomposed into a scalar part, which is irrotational, and a divergenceless vector part. Nevertheless, the rotational part of the velocity field is commonly neglected. Although this approximation works very well on linear scales, on small scales it must break down: we know that most galaxies rotate and a coherent rotational motion have been observed on even larger scales, of the order of 20 Mpc. In this talk I will discuss the generation of vorticity in N-body simulations for cold dark matter particles. Even if in the initial condition the velocity field is purely potential, velocity dispersion and vorticity are generated during the evolution due to orbit crossing of the particles and finite grid resolution. In order to study the vorticity induced by shell-crossing, we implemented the computation of the velocity field in gevolution, a relativistic code for N-body simulations. I will show the tests that we performed to assess the reliability of our method and some preliminary results on the estimation of the vorticity power spectrum and its redshift evolution. This work is relevant for improving our theoretical understanding of the rotational content of the cosmic flow and for modelling its impact on galaxy clustering in redshift space.
