Globular clusters in galaxies beyond the Local Group. V. The giant ellipticals reconsidered

The large-scale spatial structures of the globular cluster halo systems around the giant ellipticals M87 and M49 in Virgo, and NGC 3311 in Hydra I, are analyzed following a revision of the previously published star counts around these galaxies. Comparison of these three systems, and comparison with several other halo systems in galaxies of different sizes and types, has led to several new results connected with the structures of globular cluster systems in general: (a) The globular cluster systems in M87 and M49 have spatially identical structures within observational uncertainties. Both have projected logarithmic slopes α = Δ log sigma/Δ log rapprox. =-1.7 over almost the entire range of their halos. The only obvious difference between them is their total cluster population (specific frequency Sapprox. =15 for M87, Sapprox. =6 for M49). (b) Both the M87 and M49 cluster systems are spatially less centrally concentrated than the underlying halo light of the galaxies, by Δαapprox.0.7. This fundamental structural difference between subsystems of the halo is considerably more well established than in previous discussions, and applies to every measurable part of their halos from near the center out to rapprox.100 kpc. (c) The NGC 3311 cluster system is even ''flatter'' (αapprox. =-1.3) than the ones in the Virgo