Determination of the Dark Matter Profile of Abell 2199 from Integrated Starlight

We have obtained deep, long-slit spectroscopy along the major axis of NGC 6166, the cD galaxy in the cluster Abell 2199, in order to measure the kinematics of intracluster starlight at large radii. The velocity dispersion initially decreases from the central value of 300 km s, to 200 km s within a few kpc, and then steadily rises to 660 km sat a radius of 60 kpc (H0=75 km s Mpc, Ωm=0.3, ΩΛ=0.7), nearly reaching the velocity dispersion of the cluster (σA2199 = 775 ± 50 km s). These data suggest that the stars in the halo of the cD trace the potential of the cluster and that the kinematics of these intracluster stars can be used to constrain the mass profile of the cluster. In addition, we find evidence for systematic rotation (V/σ≈0.3) in the intracluster stars beyond 20 kpc. Such rotation is not seen in the kinematics of the cluster members. The surface brightness and velocity dispersion profiles can be fit using a single component mass model only by making unphysical assumptions about the level of anisotropy for both the stars in the cD galaxy and for the kinematics of the galaxies in the cluster. Two-component mass models for the cD and its halo are subsequently explored using the kinematics of known cluster members as an additional constraint on the total enclosed mass beyond the extent of the stellar kinematics. Under the assumption of isotropy, the observed major-axis kinematics can be reproduced only if the halo, parameterized by a generalizedNFW profile, has a soft core, i.e., α < 1 (a generalized-NFW halo with α = 1 is excluded due to low implied stellar mass-to-light ratios). This result is inconsistent with the predictions of current N -body simulations for dark matter halos. To test the consistency of our halo profiles with those derived from strong lensing measurements in intermediate redshift clusters, we calculate the critical radii for tangential arcs, assuming that our bestfit mass models for the Abell 2199 were placed at cosmological redshifts between 0.2 ≤ z ≤ 0.5. The calculated critical radii for our best-fit two-component isotropic models range from 5 to 40, depending on the assumed source redshift, consistent with the radii for gravitational arcs observed in intermediate redshift clusters. We also present the results of Monte Carlo simulations testing the general reliability of velocity dispersion measurements in the regime of low S/N and large intrinsic Doppler broadening. Subject headings: galaxies: elliptical and lenticular, cD, galaxies: kinematics and dynamics, galaxies: stellar content, galaxies: clusters: individual (Abell 2199), galaxies: individual (NGC 6166), (cosmology:) dark matter