Globular cluster systems. II. On the formation of old globular clusters and their sites of formation

We studied the metal-poor globular cluster populations of a large variety o f galaxies and compared their mean metallicity with the properties of the h ost galaxies. For this purpose, we constructed a comprehensive database of old metal-poor globular cluster populations, hosted by 47 galaxies, spannin g about 10 mag in absolute brightness. The mean metallicities of the system s are found to be very similar and lie in the -1.65 < [Fe/H] <less than or equal to> -1.20 range (74% of the population). Using only globular cluster systems with more than six objects detected, we find that 85% of the popula tion are within -1.65 < [Fe/H] <less than or equal to> -1.20. The relation between the mean metallicity of the metal-poor globular cluster systems and the absolute V magnitude of their host galaxies presents a very low slope that includes zero. An analysis of the correlation of the mean metallicity of the populations with other galaxy properties (such as velocity dispersio n, metallicity, and environment density) also leads to the conclusion that no strong correlation exists. The lack of correlation with galaxy propertie s suggests a formation of all metal-poor globular clusters in very similar gas fragments. A weak correlation (to be confirmed) might exist between the mean metallicity of the metal-poor clusters and the host galaxy metallicit y. This would imply that at least some fragments in which metal-poor globul ar clusters formed were already embedded in the larger dark matter halo of the final galaxy (as opposed to being independent satellites that were accr eted later). Our result suggests a homogeneous formation of metal-poor glob ular clusters in all galaxies in typical fragments of masses around 10(9)-1 0(10) M. with very similar metallicities, compatible with hierarchical form ation scenarios for galaxies. We further compare the mean metallicities of the metal-poor globular cluster populations with the typical metallicities of high-redshift objects. If we add the constraint that globular clusters n eed a high column density of gas to form, damped Ly alpha systems are the m ost likely sites among the known high-redshift objects for the formation of metal-poor globular cluster populations.