Cluster Lensing: Arcs, Arclets and Shear
This animation shows a galaxy cluster with two mass concentrations (the
pink shading indicates the projected mass density)
lensing a background field of faint blue galaxies.
In actual observations the transverse velocities are so small that there
are no observable changes over time, but I have caused the background
galaxy field to slide horizontally in order to show more examples of the
kind of highly distorted and magnified images that are possible.
Inside the Einstein ring radius one has radial arcs, and right in the
center of the cluster there are demagnified images.
The highest magnifications occur at the Einstein ring radius, giving the
large tangential arcs. Outside the Einstein ring radius there is a
systematic pattern of shear leading to tangential arclets. The
magnitude of this shear pattern can be used to determine the mass
contained within the cluster.
Abell 2218
and CL2244-02
are clusters with tangential arcs.
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© 1999 Edward
L. Wright. Last modified 30-Apr-1998