Kinematic Transitions and Streams in Galaxy Halos

The chemo-dynamics of galaxy halos beyond the Local Group may now be mapped out through the use of globular clusters and planetary nebulae as bright tracer objects, along with deep multi-slit spectroscopy of the integrated stellar light. We present results from surveying nearby early-type galaxies, including evidence for kinematically distinct halos that may reflect two-phase galaxy assembly. We also demonstrate the utility of the tracer approach in measuring the kinematics of stellar substructures around the Umbrella Galaxy, which allow us to reconstruct the progenitor properties and stream orbit. 1. Stellar halos beyond the Local Group Galaxies may generically consist of two basic components: an inner region that hosts in-situ star formation, and an outer accretion zone where satellite galaxies fall in and disrupt into halo streams and substructures. These components are reflected observationally by regions of distinct stellar densities, kinematics, dynamics, and chemical abundances. Thus these distinctions provide key information about the assembly histories of galaxies, while dynamical analyses of coherent halo substructures supply unique tests of the gravitational potential. The Milky Way is a natural focal point for studying halo transitions, substructures, and satellites, and for testing predictions from hierarchical galaxy formation theory (e.g., Carollo et al. 2007; Law & Majewski 2010; Kroupa et al. 2010; McCarthy et al. 2012). However, there are limitations to such comparisons owing to the expected stochasticity of galaxy assembly (Cooper et al. 2010). Indeed, the wealth of emerging information about the nearby galaxy M31 has revealed remarkable differences in the stellar halo properties of these two galaxies (e.g., Font et al. 2006; Deason et al. 2013). This variation highlights the need to extend detailed halo chemo-dynamical studies be1 ar X iv :1 40 1. 76 73 v1 [ as tr oph .C O ] 2 9 Ja n 20 14