  AMI observations towards CIZA J2242+5301, in comparison with observations of
weak gravitational lensing and X-ray emission from the literature, are used to
investigate the behaviour of non-baryonic dark matter (NBDM) and gas during the
merger. Analysis of the Sunyaev-Zel'dovich (SZ) signal indicates the presence
of high pressure gas elongated perpendicularly to the X-ray and weak-lensing
morphologies which, given the merger-axis constraints in the literature,
implies that high pressure gas is pushed out into a linear structure during
core passing. Simulations in the literature closely matching the inferred
merger scenario show the formation of gas density and temperature structures
perpendicular to the merger axis. These SZ observations are challenging for
modified gravity theories in which NBDM is not the dominant contributor to
galaxy-cluster gravity.
