Globular cluster systems in nearby galaxies

In this chapter we discuss the properties of globular cluster systems (GCSs) around galaxies in the Local Group and slightly beyond. The proximity of such globular clusters allows more detailed information to be obtained about some of their properties than is possible for the more distant extragalactic systems discussed in Chapter 5. This information allows for comparisons between these systems and the Galactic globular cluster system. Such comparisons show that some nearby galaxies have globular clusters very much like those of the Milky Way. However, there are also galaxies which contain young, massive star clusters that have no direct counterparts in the Galaxy. Some of these objects may be young analogs of the old globular clusters in the Milky Way and other galaxies. The M31 globular cluster system The Andromeda Galaxy (M31) is the nearest bright spiral to the Milky Way and, consequently, its globular cluster system provides an important comparison to the Galactic globular cluster system. Many of the properties of M31 suggest that it is a slightly scaled-up version of the Milky Way, being somewhat more luminous and of earlier Hubble type. One natural question is how similar the M31 globular cluster system is to the Galactic system. Starting with Hubble's (1932) identification of globular clusters in M31 and continuing through the present, observers have attempted to obtain a reliable globular cluster sample in this galaxy. Although globular clusters in M31 are expected to be fairly bright, surveying the population has been challenging for several reasons.