What can we learn from synthetic emission maps for the jet of M87?

We present a self-consistent MHD model for the jet of M87. The model consist of two distinct zones: an inner relativistic outflow and an outer cold disk-wind. While the former does not self-collimate efficiently due to its high effective inertia, the latter fulfils all the conditions for efficient collimation by the magneto-centrifugal mechanism. The relativistic flow is thus magnetically confined into a well collimated beam for a wide range of parameters.

Comparison of observed radiomaps and synthetic synchrotron emission calculated from the MHD models are used to select a best fitting model based on constraints on the opening angle and limb-brightening of the jet. We argue, that the limb-brightening is not an apparent effect, i.e. Doppler de-boosting into the line-of-sight, but due to an intrinsic accumulation of magnetic flux at the outer edge of the jet. Additionally, our model reproduces some of the properties of the optically bright knot HST-1.

Finally, we line out how linear polarisation measurements in addition to total intensity can further constrain the topology of the magnetic field in the jet beam.