Recollimation shocks in parsec-scale jets: observations and numerical simulations

The recent analysis of multi-frequency VLBI observation of jets revealed several regions of enhanced emission and increased spectral index. These regions could be interpreted as recollimiation shocks in non-pressure matched jets. We performed 2D relativistic hydrodynamic simulations of parsec-scale jets and computed the non-thermal emission in order to test this assumption. In my talk I will present recent results on the observation of jets and the results of our simulations.