Spitzer Space Telescope - General Observer Proposal #3126 A Complete IRAC Map of M31 Principal Investigator: Pauline Barmby Institution: SAO Co-Investigators: Steven Willner, SAO Michael Pahre, SAO Matthew Ashby, SAO John Huchra, SAO Robert Gehrz, University of Minnesota Elisha Polomski, University of Minnesota Charles Woodward, University of Minnesota Roberta Humphreys, University of Minnesota Karl Gordon, University of Arizona Joannah Hinz, University of Arizona Charles Engelbracht, University of Arizona Pablo Perez-Gonzalez, University of Arizona George Rieke, University of Arizona Lucianna Bianchi, Johns Hopkins University David Thilker, Johns Hopkins University Science Category: local group galaxies Observing Modes: IracMap Hours Approved: 35.5 Abstract: We propose a complete IRAC map of M31, the Andromeda Galaxy. The mid-infrared window opened by Spitzer will provide a new view of the stellar populations and dust content of this nearest large galaxy and Milky Way analog. The spatial distribution of the aromatic infrared band (AIB) emission will be compared to the UV flux distribution as revealed by GALEX, contributing to the solution of several puzzles raised by ISO observations. The AIB emission will also be compared to other indicators of star formation, such as Halpha, far-IR, and radio emission, at the highest spatial resolution possible for a large external galaxy. Populations of unusual objects such as extremely luminous stars, supernova remnants, and planetary nebulae, have already been well-studied in M31; IRAC observations will serve to characterize these populations in the mid-IR and complete their spectral energy distributions. This program complements existing GTO and Legacy observations, and will provide a rich target list for follow-up observations.