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VLT spectroscopy of globular cluster systems - I: the photometric and spectroscopic data set

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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 dierent 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 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 eective radius. Using combined optical/near-infrared colour-colour diagrams we present a method to eciently 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 Σ(R) ∼R −Γ 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 X1010 M up to 1:2X1012 M. 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.
Original languageEnglish
Pages (from-to)123-U6
JournalAstronomy and Astrophysics
Volume415
Issue number1
DOIs
Publication statusPublished - 3 Feb 2004

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