Globular clusters in the interacting galaxies NGC 1549 and NGC 1553

Globular cluster populations in the interacting early-type galaxies NGC 1549 and NGC 1553 have been identified. Starcounts on a deep Anglo- Australian Telescope prime-focus plate reveal that the globular clusters are spatially distributed in a way that seems to mimic the extrapolation of the underlying distribution of halo light. In NGC 1553 alone, there is evidence of a central deficit of clusters analogous to that seen in NGC 4486 (M87), although that finding may be an artifact of the photographic study. The azimuthal distribution of clusters around each galaxy seems random, despite the manifest interaction. Finally, the specific frequencies of the globular cluster populations are low: S(1549) = 1.0 + or - 0.5, S(1553) = 2.5 + or - 1.0. Given that NGC 1549 and NGC 1553 are in a sparse group, this finding provides yet more evidence for a picture within which the specific frequency of globular cluster populations depends to first order upon parent galaxy environment. (Author)