| 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 $\Delta t/t\approx0.3$ 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 $\la$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 $\Sigma(R)\sim R\,^{-\Gamma}$, 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 (~ $1.6{-}4.8\, R_{\rm eff}$). For the sample we find masses in the range ~ $8.8\times10^{10}~M_odot$ up to ~ $1.2\times10^{12}~M_odot$. 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.
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