43 GHz radio map. Comparison of our thermal and κ-jet model with a VLBI map of M 87 at 43 GHz. First panel from the left: 43 GHz radio map of M 87 (Janssen et al. 2019). Second panel: synchrotron map of the thermal-jet model, convolved with a 2D Gaussian beam. Third panel: same as the second panel but now for a κ-jet model with ϵ = 0.0. Fourth panel: same as the third panel but now with ϵ = 0.015. The white ellipse indicates the beam used to convolve the images. All models produce a jet that is too narrow compared to the VLBI map. The extent of the jet increases when electron acceleration is present, and is maximum for ϵ = 0.015.