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Knut Olsen |
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"The Star Formation History
of M31 and the Origin of the Ring of Fire" |
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I will discuss results derived from H and K images of six fields in the disk of M31, obtained with the NIRI instrument and ALTAIR adaptive optics system on Gemini North. These are the some of the highest resolution near-infrared observations obtained to date of the extremely crowded high surface brightness regions of M31. In earlier work, we used similar images to derive the coarse star formation histories of M31's bulge and inner disk. From fits to the M_K luminosity functions of the bulge and innermost disk fields, we found the stellar population mix to be dominated by old, nearly solar metallicity stars independent of radius. Our new fields reveal very different star formation histories. While an old, moderately metal-poor population contains the majority of the stellar mass, up to ~30% of the mass lies in what appears to be a fairly recent burst of star formation. We attribute this burst to M31's 10 kpc "Ring of Fire", an area within which M31 contains many active star forming regions. I will discuss the consequences of the star formation histories for how the 10 kpc ring may have formed. |