Simulating the Spitzer mid-IR color-color diagrams
  We use a simple parameterization of the mid-IR spectra of a wide range of galaxy types in order to predict their distribution in the Infrared Array Camera (IRAC) 3.6um, 4.5um, 5.8um, and 8.0um and Multiband Photometer for Spitzer (MIPS) 24um color-color diagrams. We distinguish three basic spectral types by the energetically dominant component in the 3--12 micron regime: stellar-dominated; PAH-dominated; and continuum-dominated. We have used a Markov chain Monte Carlo (MCMC) approach to arrive at a more systematic and robust representation of the mid-IR spectra of galaxies than more traditional approaches. We find that IRAC color-color plots are well suited to distinguishing the above spectral types, while the addition of 24 micron data allows us to suggest practical 3-color cuts which preferentially select higher redshift sources of specific type. We compare our simulations with the color-color plot obtained by the Spitzer First Look Survey (FLS) and find reasonable agreement. Lastly, we discuss other applications as well as future directions for this work. 
A.Sajina (1), M.Lacy (2), D.Scott (1) ((1) University of British   Columbia, (2), Spitzer Science Center)