VLT spectroscopy of globular cluster systems^*,**,***

I. The photometric and spectroscopic data set

¹ Sternwarte der Ludwig-Maximilians-Universität, Scheinerstr. 1, 81679 München, Germany e-mail: saglia@usm.uni-muenchen.de
² European Southern Observatory, 85749 Garching bei München, Germany e-mail: mkissler@eso.org
³ Max-Planck-Institut für extraterrestrische Physik, Giessenbachstrasse, 85748 Garching bei München, Germany e-mail: bender, maraston, dthomas@mpe.mpg.de
⁴ Grupo de Astronomía, Departamento de Física, Casilla 160-C, Universidad de Concepción, Concepción, Chile e-mail: tom@coma.cfm.udec.cl
⁵ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA e-mail: goudfroo@stsci.edu

Corresponding author: T. H. Puzia, puzia@usm.uni-muenchen.de

Received: 14 May 2003
Accepted: 11 September 2003

Abstract

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 and a metallicity resolution ~ dex, depending on the absolute metallicity. Globular cluster candidates are selected from deep FORS2/ISAAC photometry with % 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 , 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 (~). For the sample we find masses in the range ~ up to ~. 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.