Investigating [X/Fe], IMF and Compositeness in Integrated Models

We explore several existing challenges of evolutionary stellar population synthesis models in integrated light: age-metallicity degeneracy, initial mass function (IMF), elemental abundances, and compositeness.  First, we search for age-sensitive and metal-sensitive colors in three photometric systems. We also add to the discussion of optical to near-infrared Johnson-Cousins broad band colors, finding a great decrease in age sensitivity when updated isochrones are used.  Then we investigate the element abundances and compositeness of our models, in which we assume a single-peak abundance distribution and the same elemental abundance trends as the Milky Way bulge stars.  Varying the width of the abundance distribution function reveals novel ``red lean'' and ``red spread'' effects.  Next, we study three effects that co-determine the dwarf/giant ratio: the IMF slope, the IMF low mass cut-off (LMCO), and AGB star contributions.  This degeneracy can be lifted for old, metal-rich stellar populations, although at an observationally challenging level ($\approx$0.02 mag).  Finally, we select and reduce more than 200 $z\sim0.4$ red galaxy spectra from the DEEP2 sky survey, and measure the Lick-style spectral indices from the composite spectra. Multiple optical IMF-sensitive indices suggest a shallower IMF that qualitatively agrees with current literature.