Evolution of ion VDFs across the shock. Panel a shows a reduced distribution of the phase-space density along the shock normal, and we plot in panel b the magnetic field in shock coordinates. The bottom panels show ion VDFs in the plane (panels c to i) and at various locations from upstream to downstream of the shock front. refers to B_u. An ion population (in all the VDFs) that is separate from the solar wind beam is noticeable.