Mathematics – Logic
Scientific paper
Sep 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994apj...433...80h&link_type=abstract
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 433, no. 1, p. 80-86
Mathematics
Logic
21
Andromeda Galaxy, Galactic Evolution, Galactic Structure, Globular Clusters, Magellanic Clouds, Milky Way Galaxy, Star Clusters, Ellipsoids, Galactic Rotation, Oblate Spheroids, Velocity Distribution
Scientific paper
The distributions of intrinsic axis ratios are computed for the globular clusters of four different galaxies and compared to one another. We assume that globular clusters are oblate with axis ratios 1:1: gamma, and the distribution function of intrinsic axis ratio f(gamma) is Gaussian with a peak at gamma0 and standard deviation sigma0. The best-fitting distributions obtained by a Kolmogorov-Smirnov test of the distribution of projected axis ratios have gamma0 = 0.955, sigma0 = 0.130, and gamma0 = 0.930, sigma0 0.110 for the clusters in our Galaxy and M31, respectively. Whereas oblate spheroids are consistent with the shapes of the globular clusters in the Milky Way and M31, triaxial spheroids with axis ratios 1:beta:gamma seem to be more consistent with the shapes of globular clusters in the Magellanic Clouds. For the new assumption of triaxial spheroid clusters with a Gaussian distribution of axis ratios f(beta, gamma) with a peak at beta0, gamma0 and width sigma0, 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 clusters in the Large and Small Magellanic Clouds, respectively. We confirm that clusters in galaxies with similar structure, mass, and age tend to have similar shapes, and that clusters in our Galaxy and M31 are 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 variations 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 evolving with respect to time, these morphological differences seem to be due to the age difference of globular clusters in each parent galaxy.
Han Cheongho
Ryden Barbara S.
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