Globular star clusters are powerful probes of the formation epochs, assembly mechanisms, and subsequent evolution of galaxies. This is because of the association of globular cluster formation with star-forming episodes in a galaxy's history, and because globular clusters survive as largely unaltered bright beacons, particularly in galaxy halos. Globular clusters are also simple stellar populations, and thus more easily analyzed and understood. To exploit to its fullest the unique ability of globular clusters to clarify outstanding issues, including the distribution of dark matter and the star formation histories of early-type galaxies, there must be a synergy between theoretical models and observations, particularly at low redshift where galaxies may be studied in suitable detail. This approach of galactic archaeology has recently been gainfully applied in the Local Group, and it is timely to extend it to distances of dozens of megaparsecs, and thus to a more representative cross-section of the Universe. This project will focus on two key areas: 1) Galaxy assembly and the role of dark matter, that is, how and when do the building blocks of galaxies combine, and 2) Stellar populations, that is, how and when do stars form within these building blocks? It involves an unprecedented systematic survey of the fundamental properties of globular cluster systems, and how they relate to their host galaxies, with a particular focus on early-type galaxies. This is the first constructive integration of globular cluster and galaxy research in a cosmological context.
This survey will couple innovative observations using a suite of the world?s most powerful ground-based facilities with a team of world-leading researchers spanning a wide range of sub-disciplines. The landmark dataset on the chemo-dynamical properties of nearby galaxies will be scientifically fruitful for years to come. In addition, partnership with a national, non-profit organization called Science Buddies will greatly enhance the impacts of this work. The current vigorous and successful program of professional and public outreach will continue, with a proven record of successfully including women, undergraduates, and minorities in forefront research.
This research focused on the varied properties of globular star clusters (GCs) and their connections to their host galaxies. An unprecedented sample was obtained of kinematics and chemical abundances of GCs, using primarily the DEIMOS spectrograph on the Keck telescope. These publically-accessible data will not only be useful for extensive data-mining by the astronomical community, but have already yielded many novel, intriguing results, in some cases by direct comparison to theoretical models and simulations for galaxies and star clusters. These results include: * indications that GCs are connected to their host galaxies' dark matter halos; * orbital properties of GCs that contradict infall patterns predicted generically by theories of galaxy formation; * inconsistencies with the distribution of dark matter inferred using X-ray studies; * large-scale rotation of dwarf elliptical galaxies that implies these systems originally formed as disk galaxies; * dramatic transitions from the central regions of galaxies to their outer parts, suggesting that these galaxies formed in two distinct phases; * discovery of GCs in coherent motion around a large elliptical galaxy, implying the residual signature of a smaller galaxy being consumed; * identification of a new, low-luminosity species of ultra-compact dwarf, a mysterious class of objects at the intersection of star clusters and dwarf galaxies; * estimates of the primordial epoch when hydrogen gas was re-ionized, using GCs to infer that this epoch varied from galaxy to galaxy; * measurement of the masses of GCs around the nearby Andromeda galaxy, with patterns that defy standard theoretical expectations. ?The grant activities also included collaboration with the non-profit science outreach organization 'Science Buddies' which targets K-12 students, particularly those seeking science fair projects. Projects developed with globular star cluster content were widely accessed by a large and diverse population of students. A new, public science project competition was also conducted. Furthermore, extensive training of graduate students and postdocs was carried out.
