Globular Clusters, Halo Stars and Galaxy Assembly

Thu, October 08, 2015

A variety of evidence suggests that metal rich globular clusters (GCs) trace the build-up of galaxy bulges, while metal poor GCs trace the build up of their halos. Wide field observations of galaxies are critically important for testing the currently favored two-phase paradigm for galaxy formation, because many signatures of galaxy assembly processes are only revealed at large radius.  Indeed more than 90% of the total mass and angular momentum resides beyond one effective radius, the traditional limit for two dimensional spectroscopic studies of galaxies. The SLUGGS (SAGES Legacy Unifying Globular clusters and GalaxieS) survey of 25 + galaxies is producing  2-D kinematic and metallicity maps out to 3 effective radii for galaxy light, and out to 10 effective radii for GCs. These are being compared to maps generated from cosmological simulations, allowing details of two-phase galaxy assembly and the origins of GCs to emerge. SLUGGS has also revealed new classes of stellar systems that are the "smoking gun" for accretion processes. In addition, they shed light on the M-sigma relation for supermassive black holes in galaxies and may be directly relevant to the missing satellite problem in lambda CDM cosmology.