Our understanding of the formation and chemical enrichment processes of normal galaxies is largely constrained by evidence from one galaxy: the Milky Way. That evidence is largely revealed in the detailed abundance patterns of old stars, which bear the fossil record of the Galaxy's gas chemistry at the time they formed. It has never been possible to obtain similar evidence in even one other normal galaxy. This is simply because old stars beyond the nearest dwarf spheroidal galaxies of the Local Group are too faint to be observed at the high signal-to-noise and high spectral resolution needed for abundance analysis. Unlike single stars, high-resolution spectra can be obtained of unresolved globular clusters at distances as large as 4 Mpc with current telescopes. Globular clusters are bright enough and have low enough velocity dispersions that even weak lines could be detected in spectra of their integrated light. Detailed abundances have never been obtained for unresolved globular clusters only because current methods of abundance analysis only work for individual stars. A method for abundance analysis of integrated-light spectra will make it possible to measure detailed abundances in the massive galaxies of the Local Group and well beyond. To develop this technique, a training set of resolved globular clusters in the Milky Way and Large Magellanic Cloud will be created. In these training set clusters, color magnitude diagrams and fiducial metallicities from single stars can be obtained, supplying a wealth of information for developing and testing the proposed method for analyzing the integrated light spectra of unresolved globular clusters. Crucially, the training set includes globular clusters of a wide range of ages and abundances, so that the necessary strategies can be developed to deal with such variations in unresolved globular clusters. Preliminary results demonstrate the potential of this technique, with reasonable abundances being derived from the integrated spectra of NGC 6397 and 47 Tucanae. However, a number of additions/improvements will also be added here. These include incorporation of blended lines in the synthesis (including the effects of hyperfine splitting), profile matching of strong lines, and consideration of possible non-local thermodynamic equilibrium effects. In addition, issues which may affect the confidence of the results will also be explored: horizontal branch morphology and what constraints can be applied through spectral indicators (e.g., hydrogen line widths), the sensitivity to the luminosity function of stars at the low mass end, as well as the giants, and the importance of assumed alpha-element enhancements in the modeling process. This method for measuring abundances will let astronomers study the detailed chemical enrichment histories of galaxies beyond the Milky Way for the first time. This will dramatically increase the pool of observational constraints on galaxy formation theories and therefore have broad impact on our understanding of galaxy formation. The training set spectra themselves will also provide abundances of Magellanic Cloud clusters which are not yet well known, provide a calibration library for line index systems, and help astronomers understand the initial mass function of stars in globular clusters and the nucleosynthetic yields of supernovae. The training set spectra will also be made available through existing database as soon as they are published. A majority of the funding goes to supporting the training and education graduate students using state of the art observational facilities and computational tools.

Agency
National Science Foundation (NSF)
Institute
Division of Astronomical Sciences (AST)
Application #
0507350
Program Officer
Michael M. Briley
Project Start
Project End
Budget Start
2005-07-15
Budget End
2008-03-31
Support Year
Fiscal Year
2005
Total Cost
$382,036
Indirect Cost
Name
University of Michigan Ann Arbor
Department
Type
DUNS #
City
Ann Arbor
State
MI
Country
United States
Zip Code
48109