VLT Spectroscopy of Globular Cluster Systems, I. The Photometric and Spectroscopic Dataset

TL;DR

This paper provides a comprehensive spectroscopic and photometric dataset of extragalactic globular clusters across seven early-type galaxies, enabling detailed analysis of their properties, distributions, and host galaxy masses.

Contribution

It introduces high-quality spectroscopic measurements and a novel method for reducing contamination, along with detailed analysis of globular cluster systems in multiple galaxies.

Findings

Detection of bimodal color distributions in some galaxies.

Radial density profiles vary between 0.8 and 2.6.

Mass estimates of host galaxies range from 8.8e10 to 1.2e12 solar masses.

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. About 50% of our data allow an age resolution dt/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. 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 Msolar up to ~1.2*10^12 Msolar. 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. [abridged]