Shock / Shock front / Bow shock

eg. Bow shock in front of a boat; The galaxy cluster merger released energy in the form of shocks and turbulence throughout the intracluster medium.

Intracluster Medium

The Intracluster Medium is the very hot (several millions of degrees), low-density, diffuse plasma (gas) in between galaxies inside a galaxy cluster.

entropy / enthalpy

eg. The entropy traces the gas history of the system. The internal enthalpy causes the bubbles to buoyantly rise.

gradient

It forms a gradient to the closest minimum.

redshift

The redshift of the galaxy cluster is quite high.

background

eg. The background galaxies, instrumental background, astrophysical background, background signal

Dark Matter

The gas traces the dark matter separation from the galaxy.

Cluster

eg. Galaxy cluster, a cluster of galaxies