Collaborative Research: Age-Dating M31's Halo and Satellites - Testing the Lambda CDM Paradigm

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Stellar halos, the roughly spherical clould of stars orbiting a spiral galaxy, provide unique insight into the formation and evolution of galaxies, and they may hold the key to understanding dark matter. From our position inside the Milky Way, we are unable to fully probe our own halo, because much of it is blocked from our view. M31 (the "Andromeda Galaxy") is near enough that we can measure properties of individual stars in its halo. This program will utilize existing data and obtain new observations of M31 in order to map the distribution star ages throughout its halo. This will permit them to determine the relative importance of several different mechanisms that can add stars to a galaxy halo. Ultimately, this will lead to a better understanding of the history of our own Milky Way galaxy. This program will create opportunities for both undergraduate and graduate student research at two institutions. The University of Virginia group works with amateur astronomers on galaxy evolution research projects and outreach programs to K-12 students in rural Virginia. The University of California - Santa Cruz team teaches underrepresented high school students through the COSMOS, MAGIC, and the Science Internship Programs. Both of the PIs teach large undergraduate courses, actively mentor students, give regular public lectures and speak in K-12 classrooms.The PIs will create the first age-distribution profile of the M31 stellar halo. This work leverages an enormous investment of telescope time over the past 10 years (the SPLASH project) and aims to add two significant new parameters: metallicity and age distributions. Three new observational methods will be applied, including a near infrared imaging survey across the M31 halo out to a distance of 180 kpc, optical time series of anomalous Cepheids in M31 satellite galaxies, and Keck/DEIMOS spectroscopy of M31 field and dSph stars. This work leverages an enormous investment of telescope time over the past 10 years (the SPLASH project) and aims to add two significant new parameters: metallicity and age distributions.