The structure and stellar content of the central region of M33

Using Gemini QuickStart infrared observations of the central 22 of M33, we analyze the stellar populations in this controversial region. Based on the slope of the giant branch we estimate the mean metallicity to be -0.26+/-0.27, and from the luminosities of the most luminous stars, we estimate that there were two bursts of star formation, similar to2 and similar to0.5 Gyr ago. We show that the stellar luminosity function not has only a different bright end cutoff, but also a significantly different slope than that of the Galactic bulge, and we suggest that this difference is due to the young stellar component in M33. We combine our infrared Gemini data with optical Hubble Space Telescope Wide Field Planetary Camera 2 measurements revealing a color-magnitude diagram populated with young, intermediate-age, and old stellar populations. Using surface brightness profiles from 0.1 to 18', we perform simple decompositions and show that the data are best fitted by a three-component core plus bulge plus disk model. Finally, we find no evidence for radial variations of the stellar populations in the inner 3-10 of M33, based on a spatial analysis of the color-magnitude diagrams and luminosity functions.