Hydrodynamics with a Zoom Region
Baryons, and therefore the hydrodynamics tasks, are isolated to the high resolution zoom region. This means baryons that leave the zoom region will no longer have their properties updated.
This is another of the many reasons why padding the zoom region beyond the extent of the high resolution particles is so important. Choose too small a value for ZoomRegion:region_pad_factor and baryons will leave the zoom region regularly. Choose too large a value and the zoom region will be poorly resolved losing the efficiency gains from introducing the higher resolution zoom cells.
Pressureless Boundary
Only having high resolution baryons introduces a pressureless boundary at the edge of the high resolution particle distribution…