To appear in the proceedings of "Galaxy Evolution: Emerging Insights and Future Challenges," 11-14 November 2008, Austin, USA
astro-ph/0901.2577

For a PDF version of the article, click here.

THE STAR FORMATION HISTORIES OF THE M31 AND M33 SPHEROIDS

Thomas M. Brown


Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 USA


I review the observational constraints on the star formation histories in the spheroids of M33 and M31, the other two spiral galaxies in the Local Group. M33 does not possess a traditional bulge; instead, it has a small nuclear region hosting stars with a wide range of ages. The star formation history of the M33 halo is poorly constrained, but composite spectra of its halo globular clusters imply a wide age spread of 5-7 years, while the presence of RR Lyrae stars in the halo implies at least some of the population is ancient. Although it is possible to obtain the detailed star formation history of the M33 halo via deep photometry, this has not been done to date. M31 hosts a traditional bulge that is apparently dominated by stars older than 10 Gyr. Deep photometry of the M31 halo demonstrates that it hosts both a population of ancient metal-poor stars and a significant population extending to younger ages and high metallicity, apparently due to its active merger history.


Table of Contents

INTRODUCTION

AGE CONSTRAINTS

M33 SPHEROID
M33 Bulge
M33 Halo

M31 SPHEROID
M31 Bulge
M31 Halo

SUMMARY

REFERENCES

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