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Symposium 241

Abstract details

The Star Formation History of M33's Outer Regions
M. K. Barker, A. Sarajedini, D. Geisler, P. Harding, R. Schommer

We present VI photometry obtained with the Advanced Camera for Surveys for three fields located $\sim 4 - 6$ visual scale lengths in deprojected radius southeast of M33's nucleus. The color-magnitude diagrams reveal a mixed stellar population with masses as high as $\sim 5 M_{\sun}$ down to $\sim 1 M_{\sun}$. The stellar surface density drops off exponentially with a scale length that increases with age suggesting, but not requiring, the action of orbital diffusion. Using the IAC-star (Aparicio \& Gallart 2004) and StarFISH (Harris \& Zaritsky 2001) programs in conjunction with the Padova (Girardi et al.\ 2000) and Teramo (Pietrinferni et al.\ 2004) stellar tracks we have also derived the star formation history in these fields. Both sets of tracks predict the mean age to increase from $\sim 6$ Gyr to $\sim 8$ Gyr and the mean global metallicity to decrease from $\sim -0.7$ to $\sim -0.9$ as galactocentric radius increases.

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