Wide-field kinematics of globular clusters in the Leo i group

Abstract

We present wide-field spectroscopy of globular clusters around the Leo I group galaxies NGC 3379 and NGC 3384 using the FLAMES multi-fibre instrument at the VLT. We obtain accurate radial velocities for 42 globular clusters (GCs) in total, 30 for GCs around the elliptical NGC 3379, eight around the lenticular NGC 3384, and four which may be associated with either galaxy. These data are notable for their large radial range extending from 0′.7 to 14′.5 (2 to 42 kpc) from the centre of NGC 3379, and small velocity uncertainties of about 10 km s-1. We combine our sample of 30 radial velocities for globular clusters around NGC 3379 with 8 additional GC velocities from the literature, and find a projected velocity dispersion of σp = 175-22+24 kms-1 at R < 5′ and σp = 147-39+44 at R > 5′. These velocity dispersions are consistent with a dark matter halo around NGC 3379 with a concentration in the range expected from a ACDM cosmological model and a total mass of ≈ 6 × 1011 M⊙. Such a model is also consistent with the stellar velocity dispersion at small radii and the rotation of the HI ring at large radii, and has a (M/L)B that increases by a factor of five from several kpc to 100 kpc. Our velocity dispersion for the globular cluster system of NGC 3379 is somewhat higher than that found for the planetary nebulae (PNe) in the inner region covered by the PN data, and we discuss possible reasons for this difference. For NGC 3384, we find the GC system has a rotation signature broadly similar to that seen in other kinematic probes of this SBO galaxy. This suggests that significant rotation may not be unusual in the GC systems of disc galaxies. © ESO 2006.