Astronomy Colloquium

Since more than 90% of the total mass and angular momentum in galaxies resides beyond one effective radius, wide field observations are crucial for  understanding the assembly histories of galaxies. The SLUGGS survey is producing 2-dimensional kinematic and metallicity maps for globular clusters (GCs) out to 10 effective radii and galaxy starlight out  to 3 effective radii in 28 nearby early-type galaxies.   Data obtained with Suprime-Cam on  Subaru and DEIMOS on Keck are being compared to a variety of simulations of galaxy build-up and are found to support and constrain two-phase galaxy formation scenarios.  Early "in situ" formation and subsequent minor mergers appear to be the dominant mechanisms for building galaxies and their GC systems. Later major mergers may have been  important only in a small minority of cases. We find that the behavior of galaxies in their central regions  is a surprisingly poor predictor of large scale trends. I will also explore  the relationships between the different types of compact stellar systems, including
a newly discovered class of faint ultra compact dwarfs (UCDs) that may be markers of the halo assembly process.