Identikit Parameters

Abstract representation of the parameter space for an encounter of two disk galaxies. The radial coordinate encompasses the parameters describing the relative orbit. The angular coordinate represents the angles which specify the orientations of the two disks. The vertical coordinate includes the time since pericenter, viewing angles, and scale factors.

A conventional N-body simulation starts at a single point on the horizontal plane and explores the dotted line above it. In contrast, a single Identikit simulation can explore the entire surface of the cylinder.

  Identikit parameters

Orbit Parameters

Assuming that the two galaxies were originally well-separated, their initial orbit will approximate a Keplerian orbit of two point masses. The parameters used to specify this ideal orbit are:

Since a separate Identikit simulation must be run for each combination of orbit parameters (p, μ, e), these parameters are chosen from a set of available values. At present, eight values of p and two values of μ are available, while e is fixed at e = 1 (parabolic orbit).

Disk Orientations

The initial Keplerian orbit is confined to the (x, y) plane, with its angular momentum vector along the positive z axis. The orbit is oriented so that the point masses lie on the x axis at pericenter. The orientation of each disk with respect to this orbit is specified by two parameters:

Viewing Parameters

The next set of parameters specifies how a simulation is viewed once it has been run.

Image Parameters

Joshua E. Barnes      (barnes at
Updated: 31 March 2011
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