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NGC 3311 is the central cD galaxy of the Hydra I cluster. We use globularclusters around NGC 3311, combined with kinematical data of the galaxy itself,to investigate the dark matter distribution in the central region of Hydra I.Radial velocities of 118 bright globular clusters, based on VLT/VIMOS maskspectroscopy, are used to calculate velocity dispersions which are well definedout to 100 kpc. NGC 3311 is the most distant galaxy for which this kind ofstudy has been performed. We also determine velocity dispersions of the stellarcomponent from long slit spectroscopy out to 20 kpc. Moreover, we present a newphotometric model for NGC 3311 in the V-band. We search for a dark halo whichin the context of a spherical Jeans model. We also compare the radial velocitydistributions of globular clusters and planetary nebulae. The projected stellarvelocity dispersion rises from 185 km/s to 350 km/s at a radius of 20 kpc. Theglobular cluster dispersion rises as well from 500 km/s at 10 kpc to about 800km/s at 100 kpc, comparable to the velocity dispersion of the cluster galaxies.A dark matter halo with a core reproduces well the velocity dispersions ofstars and globular clusters simultaneously under isotropy. The central stellarvelocity dispersions predicted by cosmological NFW halos are less goodrepresentations, while the globular clusters allow a wide range of haloparameters. A suspected radial anisotropy of the stellar population aggravatesthe deviations. However, we find discrepancies with previous kinematical data,which we cannot resolve and may indicate a more complicated velocity pattern.Although one cannot conclusively demonstrate that the dark matter halo of NGC3311 has a core rather than a cusp, a core seems to be preferred by the presentdata. A more complete velocity field and an analysis of the anisotropy isrequired to reach firm conclusions.

The dark halo of the Hydra I galaxy cluster: core, cusp, cosmological? Dynamics of NGC 3311 and its globular cluster system