Morphology of galactic globular clusters

Abstract

We study shapes and sizes of 110 Galactic globular clusters (GCs) with the 2MASS Point Source Catalog. In general, Galactic GCs have spherical halos, with a median flattening of 0.1. GCs closer to the bulge show more circularized shapes and have smaller physical sizes. Intrinsically more luminous clusters, hence perhaps more massive, tend to be more circularized. Six GCs are highly flattened with flattening ≥ 0.3 Arp 2 and Pal 12 are known to be associated with the streamer of the Sagittarius dwarf galaxy. Pal 5 is being cannibalized by the Milky Way, UKS 1 and NGC 6355 are bulge globular clusters suffering strong tidal distortion. NGC 2419 is a halo member with a Galactocentric distance 90 kpc. Its flattened shape can not be accounted for. It may well be the remnant core of an already dissolved dwarf galaxy.