Assessing the Milky Way Satellites Associated with the Sagittarius Dwarf Spheroidal Galaxy

Numerical models of the tidal disruption of the Sagittarius (Sgr) dwarf galaxy have recently been developed that for the first time simultaneously satisfy most observational constraints on the angular position, distance, and radial velocity trends of both leading and trailing tidal streams emanating from the dwarf. We use these dynamical models in combination with extant 3-D position and velocity data for Galactic globular clusters and dSph galaxies to identify those Milky Way satellites that are likely to have originally formed in Sgr and been stripped from it during its extended interaction with the Milky Way. We conclude that the globular clusters Arp 2, M 54, NGC 5634, Terzan 8, and Whiting 1 are likely associated with the Sgr dwarf, and that Berkeley 29, NGC 5053, Pal 12, and Terzan 7 may be as well. The initial Sgr system therefore may have contained 5-9 globular clusters, corresponding to a specific frequency S_N = 5 - 9 for an initial Sgr luminosity M_V = -15.0. Our result is consistent with the 8\pm2 Sgr globular clusters expected from statistical modeling of the Galactic globular cluster distribution and the corresponding false-association rate due to chance alignments with the Sgr streams. These clusters are consistent with previous reconstructions of the Sgr age-metallicity relation, and show no evidence for a second-parameter effect shaping their horizontal branch morphologies. We find no statistically significant evidence to suggest that any of the recently discovered population of ultra-faint dwarf galaxies are conclusively associated with the Sgr tidal streams. (Abridged).Comment: 25 pages, 12 figures. Accepted for publication in ApJ. Version with full-resolution figures is available at http://www.astro.ucla.edu/~drlaw/Papers/Sgr_clusters.pd

The Future of Stellar Populations Studies in the Milky Way and the Local Group

The last decade has seen enormous progress in understanding the structure of the Milky Way and neighboring galaxies via the production of large-scale digital surveys of the sky like 2MASS and SDSS, as well as specialized, counterpart imaging surveys of other Local Group systems. Apart from providing snaphots of galaxy structure, these "cartographic" surveys lend insights into the formation and evolution of galaxies when supplemented with additional data (e.g., spectroscopy, astrometry) and when referenced to theoretical models and simulations of galaxy evolution. These increasingly sophisticated simulations are making ever more specific predictions about the detailed chemistry and dynamics of stellar populations in galaxies. To fully exploit, test and constrain these theoretical ventures demands similar commitments of observational effort as has been plied into the previous imaging surveys to fill out other dimensions of parameter space with statistically significant intensity. Fortunately the future of large-scale stellar population studies is bright with a number of grand projects on the horizon that collectively will contribute a breathtaking volume of information on individual stars in Local Group galaxies.Comment: 12 pages, 0 figures, IAU Symposium No. 262, Stellar Populations - Planning for the Next Decad