THE INTRINSIC SHAPES OF ELLIPTIC GALAXIES

The luminosity-weighted axis ratios are computed for a sample of 171 elliptical galaxies observed by Djorgovski. The apparent axis ratios are used to constrain the intrinisic shape of elliptical galaxies. It is assumed that elliptical galaxies are triaxial ellipsoids with axis ratios 1:beta:gamma, and that the distribution of intrinsic axis ratios f(beta, gamma) has an isotropic Gaussian form, with a peak at the position beta-0, gamma-0 and width-sigma-0. The best-fitting distribution as measured by Kolmogorov-Smirnov and chi-2 tests of the distribution of projected axis ratios, has beta-0 = 0.98, gamma-0 = 0.69, and sigma-0 = 0. 11. If elliptical galaxies rotate around their shortest principal axis, this distribution of shapes cannot explain the observed frequency of galaxies with misalignments of approximately 90-degrees between their rotation axes and apparent minor axes; some elliptical galaxies must rotate around their longest principal axes. The shapes of clusters of galaxies are best fitted by a distribution f(beta, gamma) with sigma-0 = 162, beta-0 = 0.67, and gamma-0 = 0.45. Galaxy halos which form by dissipationless collapse are close in shape to the observed clusters than to the observed elliptical galaxies; the relative roundness of elliptical galaxies must be rooted in dissipational processes.