The dynamically hot stellar halo around NGC 3311: a small
  cluster-dominated central galaxy
  An important open question is the relation between intracluster light and the
halos of central galaxies in galaxy clusters. Here we report results from an on
going project with the aim to characterize the dynamical state in the core of
the Hydra I (Abell 1060) cluster around NGC 3311. Methods: We analyze deep
long-slit absorption line spectra reaching out to ~25 kpc in the halo of NGC
3311. Results: We find a very steep increase in the velocity dispersion profile
from a central sigma_0=150 km/s to sigma_out ~450 km/s at R ~ 12 kpc. Farther
out, to ~25 kpc, sigma appears to be constant at this value, which is ~60% of
the velocity dispersion of the Hydra I galaxies. With its dynamically hot halo
kinematics, NGC 3311 is unlike other normal early-type galaxies. Conclusions:
These results and the large amount of dark matter inferred from X-rays around
NGC 3311 suggest that the stellar halo of this galaxy is dominated by the
central intracluster stars of the cluster, and that the transition from
predominantly galaxy-bound stars to cluster stars occurs in the radial range 4
to 12 kpc from the center of NGC 3311. We comment on the wide range of halo
kinematics observed in cluster central galaxies, depending on the evolutionary
state of their host clusters.
