A COMPARISON OF THE INTRINSIC SHAPES OF GLOBULAR-CLUSTERS IN 4 DIFFERENT GALAXIES

The distributions of intrinsic axis ratios are computed for the globul ar cluster of four different galaxies and compared to one another. We assume that globular clusters are oblate with axis ratios 1:1:gamma, a nd the distribution function of intrinsic axis ratio f(gamma) is Gauss ian with a peak at gamma0 and standard deviation sigma0. The best-fitt ing distributions obtained by a Kolmogorov-Smirnov test of the distrib ution of projected axis ratios have gamma0 = 0.955, sigma0 = 0.130, an d gamma0 = 0.930, sigma0 = 0.110 for the clusters in our Galaxy and M3 1, respectively. Whereas oblate spheroids are consistent with the shap es of the globular clusters in the Milky Way and M31, triaxial spheroi ds with axis ratios 1:beta:gamma seem to be more consistent with the s hapes of globular clusters in the Magellanic Clouds. For the new assum ption of triaxial spheroid clusters with a Gaussian distribution of ax is ratios f(beta, gamma) with a peak at beta0, gamma0, and width sigma 0, the best-fitting distributions have beta0 = 0.856, gamma0 = 0.742, sigma0 = 0.005 and beta0 = 0.917, gamma0 = 0.717, sigma0 = 0.000 for c lusters in the Large and Small Magellanic Clouds, respectively. We con firm that clusters in galaxies with similar structure, mass, and age t end to have similar shapes, and that clusters in our Galaxy and M31 ar e much more spherical than those in the Magellanic Clouds. It is also found that there is very small variation of the intrinsic shapes among Magellanic Cloud globulars, but there exists comparatively large vari ations in the shapes of globular clusters in the Galaxy and M31. Since the globular rotation and anisotropic internal velocity distribution, which are responsible for the shapes of the globular clusters, are ev olving with respect to time, these morphological differences seem to b e due to the age difference of globular clusters in each parent galaxy .