Published in Proc. IAU Symp. 220, "Dark matter in galaxies", ed. S. Ryder, D.J. Pisano, M. Walker, & K. Freeman (San Francisco: ASP), 2004.

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A. J. Romanowsky 1, N. G. Douglas 2, K. Kuijken 2,3, M. R. Merrifield 1, M. Arnaboldi 4, N. R. Napolitano 2, H. Merrett 1, M. Capaccioli 5, K. C. Freeman 6, O. Gerhard 7

1 School of Physics and Astronomy, University of Nottingham; 2 Kapteyn Institute, Groningen; 3 Leiden Observatory; 4 INAF–Osservatorio Astronomico di Pino Torinese, Turin; 5 INAF–Osservatorio Astronomico di Capodimonte, Naples; 6 RSAA, Mt. Stromlo and Siding Spring Observatories; 7 Astronomisches Institut, Universität Basel

Abstract: Planetary nebulae (PNe) may be the most promising tracers in the halos of early-type galaxies. We have used multi-object spectrographs on the WHT and the VLT, and the new Planetary Nebula Spectrograph on the WHT, to obtain hundreds of PN velocities in a small sample of nearby galaxies. These ellipticals show weak halo rotation, which may be consistent with ab initio models of galaxy formation, but not with more detailed major merger simulations. The galaxies near L* show evidence of a universal declining velocity dispersion profile, and dynamical models indicate the presence of little dark matter within 5 Reff — implying halos either not as massive or not as centrally concentrated as CDM predicts.

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