De Vaucouleur's law
Encyclopedia
de Vaucouleurs' law describes how the surface brightness 
of an elliptical galaxy
varies as a function of apparent distance
from the center:
By defining Re as the radius of the isophote containing half the luminosity (i.e., the radius of the inner disk contributing half the brightness of the galaxy), de Vaucouleurs' law may be written:
or
where Ie is the surface brightness at Re. This can be confirmed by noting
de Vaucouleurs' law is a special case of Sersic's law, with Sersic index n=4. A number of density laws that approximately reproduce de Vaucouleurs' law after projection onto the plane of the sky include Jaffe's model
and Dehnen's model.
of an elliptical galaxyElliptical galaxy
An elliptical galaxy is a galaxy having an approximately ellipsoidal shape and a smooth, nearly featureless brightness profile. They range in shape from nearly spherical to highly flat and in size from hundreds of millions to over one trillion stars...
varies as a function of apparent distance
from the center:By defining Re as the radius of the isophote containing half the luminosity (i.e., the radius of the inner disk contributing half the brightness of the galaxy), de Vaucouleurs' law may be written:
or
where Ie is the surface brightness at Re. This can be confirmed by noting
de Vaucouleurs' law is a special case of Sersic's law, with Sersic index n=4. A number of density laws that approximately reproduce de Vaucouleurs' law after projection onto the plane of the sky include Jaffe's model
Jaffe profile
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...
and Dehnen's model.