This paper reviews some of the observational properties of globular cluster systems, with a particular focus on those that constrain and inform models of the formation and dynamical evolution of globular cluster systems. I first discuss the observati
onal determination of the globular cluster luminosity and mass function. I show results from new very deep HST data on the M87 globular cluster system, and discuss how these constrain models of evaporation and the dynamical evolution of globular clusters. The second subject of this review is the question of how to account for the observed constancy of the globular cluster mass function with distance from the center of the host galaxy. The problem is that a radial trend is expected for isotropic cluster orbits, and while the orbits are observed to be roughly isotropic, no radial trend in the globular cluster system is observed. I review three extant proposals to account for this, and discuss observations and calculations that might determine which of these is most correct. The final subject is the origin of the very weak mass-radius relation observed for globular clusters. I discuss how this strongly constrains how globular clusters form and evolve. I also note that the only viable current proposal to account for the observed weak mass-radius relation naturally affects the globular cluster mass function, and that these two problems may be related.
We present the discovery of [OIII] 5007 emission associated with the black hole X-ray binary recently identified in a globular cluster in the Virgo elliptical galaxy NGC 4472. This object is the first confirmed black-hole X-ray binary in a globular c
luster. The identification of [OIII] 5007 emission from the black-hole hosting globular cluster is based on two independent fiber spectra obtained at the VLT with FLAMES, which cover a wavelength range of 5000-5800 Angstrom at a spectral resolution of about 6000. In each of these spectra we find an emission line at 5031.2 Angstrom with an uncertainty of several tenths of an Angstrom. These are consistent with [OIII] 5007 emission at the 1475 +/- 7 km/s radial velocity of the globular cluster previously determined from an analysis of its absorption lines. This agreement within the small uncertainties argues strongly in favor of the interpretation of the line as [OIII] 5007 emission from the black-hole hosting globular cluster. We also find that the emission line most likely has a velocity width of several hundred km/s. Such a velocity width rules out a planetary nebula explanation for the [OIII] 5007 emission and implicates the black hole as the source of the power driving the nebular emission.
