Intinsic Shapes of Elliptical Galaxies

 When an elliptical galaxy galaxy is observed its large distance from us only allow us to see its 2D projection. Unless a number of assumptions are made the true 3D shape can not be infered from its light distribution alone.
       Through the doppler shift of the star light emmited from the galaxy it is possible to calculate the line-of-sight velocity at different positions. By applying a Monte Carlo method developed by Thomas Statler to this information and the information gained from the light distribution, a Bayesian likelihood distribution of possible shapes can be derived.
Shown below is the shape likelihood distributions derived for nine galaxies.

    T is known as the triaxiality of the galaxy and CL the short to long axis ratio. A triaxiality of 1 would mean that the galaxy is shaped like a cigar and a triaxiality of zero means that the galaxy is shaped more like a flying saucer.

    From the sample of likelihood distribitions from the sample of individual galaxies above it is possible to derive the shape distribution from which all galaxies are drawn. This is done using an iterative Bayesian procedure developed by Jakob Bak and Thomas Statler. The results depend on certain assumptions regarding the underlying dynamics of the galaxies but the most general results is shown below.
 
 

    The plot marked a) is the parent distribution using LOS velocity data as well as photometric (light distribution) data. The plot marked b) is the parent distribution derived without the use of the LOS velocity data. The inabilty to make any predictions based solely on photometric data is obvious.