Annu. Rev. Astron. Astrophys. 1991. 29: 239-274 Copyright © 1991 by Annual Reviews. All rights reserved

3.4.2 OTHER TESTS The apparent surface brightness and velocity dispersion for a galaxy are expected to correlate with the apparent ellipticity, depending on the intrinsic shape of the galaxy. No conclusive results have been obtained from this type of test (200, 224, 286). Merritt showed that high accuracy data are needed (235); recent results on the fundamental plane of galaxies (94, 97) indicate that galaxies are a true two-parameter family, making it difficult to disentangle projection effects from intrinsic variations.

The interpretation of photometry alone is very uncertain. Isophotal twists are generally thought to be due to triaxial shapes (373, 374). However, the validity of this assumption is not certain, as some twists may be intrinsic (189). The correlation of twists with apparent ellipticity has been used to constrain the intrinsic shapes (22, 133), but these results are rather model dependent. The twists can constrain the change in triaxiality as a function of radius.