SIMBAD references

Globular cluster systems are valuable tools for understanding the early history of galaxy formation and, in the past two decades, there has been considerable effort devoted to studies of globular clusters in external galaxies. There are now more than 60 galaxies for which we know such cluster system properties as total population, radial distribution, luminosity distribution and color (metallicity?) distribution. While most cluster systems appear to have similar characteristics from galaxy to galaxy, the color distributions obtained so far are less uniform. Many are broader and much less strongly peaked than the galactic cluster system color/metallicity distribution; some systems contain extremely blue clusters and many contain clusters which are much redder than the reddest galactic globular clusters and presumably, more metal rich. However, these results are based primarily on broad-band photometry and spectroscopic data are sorely needed. Spectral line indices will lead to improved metallicity estimates for these globular clusters, but the interpretation is hampered by several effects including range in age and calibration of the indices for metallicities greater than the most metal-rich galactic globular clusters. If these problems can be surmounted, there is much to learn about the heavy element enrichment history in galaxies.