Letter to the Editor

Globular clusters and dwarf galaxies in Fornax^*,**

I. Kinematics in the cluster core from multi-object spectroscopy

¹ Instituto de Astrofísica de Andalucía, C/ Camino Bajo de Huétor 50, 18008 Granada, España e-mail: gbergond@caha.es
² Observatoire de Paris, GEPI (CNRS UMR 8111 & Université Paris 7), 5 place Jules Janssen, 92195 Meudon, France
³ Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824, USA
⁴ Observatoire de Marseille, 2 place Le Verrier, 13248 Marseille Cedex 04, France
⁵ Instituto de Radioastronomía Milimétrica (IRAM), Avda. Divina Pastora 7, local 20, 18012 Granada, España
⁶ Observatoire de Paris, LUTH (CNRS UMR 8102 & Université Paris 7), 5 place Jules Janssen, 92195 Meudon, France
⁷ Astronomy department, Univ. of Florida, 211 Bryant Space Science Center, PO Box 112055, Gainesville, FL 32611, USA
⁸ École Polytechnique Fédérale de Lausanne (EPFL), Laboratoire d'Astrophysique, Observatoire, 1290 Sauverny, Suisse
⁹ Centre de Recherches Astronomiques, Université Lyon 1, Observatoire de Lyon, 69561 Saint Genis Laval Cedex, France

Received: 18 December 2006
Accepted: 11 January 2007

Abstract

Aims.We acquired radial velocities of a significant number of globular clusters (GCs) on wide fields between galaxies in the nearby Fornax cluster of galaxies, in order to derive their velocity dispersion radial profile and to probe the dynamics of the cluster.

Methods.We used FLAMES on the VLT to obtain accurate velocities for 149 GCs, within a ≈500  150 kpc strip centered on NGC 1399, the Fornax central galaxy. These objects are at the very bright tail () of the GC luminosity function, overlapping the so-called “ultra-compact dwarfs” magnitude range. Eight of the brightest FLAMES-confirmed members indeed show hints of resolution in the subarcsecond pre-imaging data we used for selecting the ~500 targets for FLAMES spectroscopy.

Results.Ignoring the GCs around galaxies by applying 3d₂₅ diameter masks, we find 61 GCs of 20.0  22.2 lying in the intra-cluster (IC) medium. The velocity dispersion of the population of ICGCs is 200 km s^-1 at ~150 kpc from the central NGC 1399 and rises to nearly 400 km s^-1 at 200 kpc, a value which compares with the velocity dispersion of the population of dwarf galaxies, thought to be infalling from the surroundings of the cluster.