Jaffe profile
Encyclopedia
The Jaffe profile is a mathematical function that is used to describe the distribution of mass or light in elliptical galaxies and the bulges
of spiral galaxies. It was proposed by Walter Jaffe in 1983. Its usefulness derives from the fact that it accurately reproduces a de Vaucouleurs profile when projected onto the sky.
The density in the Jaffe model is given by
In this equation,
and 
are parameters that can be varied to fit the observed density.
Jaffe described how he arrived at his model:
Variations on Jaffe's law include the Hernquist profile, the Dehnen profile and the NFW profile, which have a similar functional form as Jaffe's law but which use different values for the two exponents.
Bulge (astronomy)
In astronomy, a bulge is a tightly packed group of stars within a larger formation. The term almost exclusively refers to the central group of stars found in most spiral galaxies...
of spiral galaxies. It was proposed by Walter Jaffe in 1983. Its usefulness derives from the fact that it accurately reproduces a de Vaucouleurs profile when projected onto the sky.
The density in the Jaffe model is given by
In this equation,
and are parameters that can be varied to fit the observed density.Jaffe described how he arrived at his model:
[The formula] was derived heuristically from the observation that the brightness profiles of spherical galaxies seem to run asand
in at least some parts of their envelopes and cores, respectively. This would imply that the spatial density runs as
and
.
Variations on Jaffe's law include the Hernquist profile, the Dehnen profile and the NFW profile, which have a similar functional form as Jaffe's law but which use different values for the two exponents.