SCYON Abstract

Received on December 15 2003

VLT Spectroscopy of Globular Cluster Systems

AuthorsThomas H. Puzia1, Markus Kissler-Patig2, Daniel Thomas3, Claudia Maraston3, Roberto P. Saglia1, Ralf Bender1, 3, Tom Richtler4, Paul Goudfrooij5, Maren Hempel2
Affiliation1 Sternwarte der Ludwig-Maximilians-Universität, Scheinerstr. 1, 81679 München, Germany,
2European Southern Observatory, 85749 Garching bei München, Germany,
3Max-Planck-Institut für extraterrestrische Physik, Giessenbachstrasse, 85748 Garching bei München, Germany,
4Grupo de Astronomía, Departamento de Física, Casilla 160-C, Universidad de Concepción, Concepción, Chile,
5Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
Accepted by Astronomy & Astrophysics


We present Lick line-index measurements of extragalactic globular clusters in seven early-type galaxies (NGC 1380, 2434, 3115, 3379, 3585, 5846, and 7192) with different morphological types (E--S0) located in field and group/cluster environments. High-quality spectra were taken with the FORS2 instrument at ESO's Very Large Telescope. ~50% of our data allows an age resolution Delta t/t ~ 0.3 and a metallicity resolution ~0.25-0.4 dex, depending on the absolute metallicity. Globular cluster candidates are selected from deep B, V, R, I, K FORS2/ISAAC photometry with 80-100% success rate inside one effective radius. Using combined optical/near-infrared colour-colour diagrams we present a method to efficiently reduce fore-/background contamination down to < 10%. We find clear signs for bi-modality in the globular cluster colour distributions of NGC 1380, 3115, and 3585. The colour distributions of globular clusters in NGC~2434, 3379, 5846, and 7192 are consistent with a broad single-peak distribution. For the analysed globular cluster systems the slopes of projected radial surface density profiles, of the form Sigma(R) ~ R-Gamma, vary between ~ 0.8 and 2.6. Blue and red globular cluster sub-populations show similar slopes in the clearly bi-modal systems. For galaxies with single-peak globular cluster colour distributions, there is a hint that the blue cluster system seems to have a more extended radial distribution than the red one. Using globular clusters as a tracer population we determine total dynamical masses of host galaxies out to large radii (~ 1.6 - 4.8 Reff). For the sample we find masses in the range ~8.8 10^10 Mo up to ~1.2 10^12 Mo. The line index data presented here will be used in accompanying papers of this series to derive ages, metallicities and abundance ratios. A compilation of currently available high-quality Lick index measurements for globular clusters in elliptical, lenticular, and late-type galaxies is provided and will serve to augment the current data set.