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Published June 1998 | Published + Accepted Version
Journal Article Open

An Old Cluster in NGC 6822


We present spectroscopy of two clusters in the dwarf irregular galaxy NGC 6822. From these we deduce an age for cluster VII of 11 ^(+4)_(-3) Gyr and [Fe/H] = -1.95 ± 0.15 dex. Cluster VII appears to be an analog of the metal-poor Galactic globular clusters. Cluster VI is found to be much younger and more metal-rich, with an age of approximately 2 Gyr. Its derived metallicity, [Fe/H] ≈ -1.0 dex, is comparable to that of the gas seen today in NGC 6822. The existence of a metal-poor old cluster in NGC 6822 rules out models for the chemical evolution of this galaxy with significant prompt initial enhancement. We find that a star formation rate that is constant with time and is within a factor of 2 of the present star formation rate can reproduce the two points on the age-metallicity relationship for NGC 6822 over the past 10 Gyr defined by these two clusters.

Additional Information

© 1998. The American Astronomical Society. Received 1998 February 25. The entire Keck/LRIS user community owes a huge debt to Jerry Nelson, Gerry Smith, Bev Oke, and many other people who have worked to make the Keck Telescope and LRIS a reality. We are grateful to the W. M. Keck Foundation, and particularly its late president, Howard Keck, for the vision to fund the construction of the W. M. Keck Observatory. J. G. C. is grateful for support from NSF grant AST 96-16729. J. P. B. is grateful to the Sherman Fairchild Foundation for support.

Attached Files

Published - Cohen_1998_AJ_115_2356.pdf

Accepted Version - 9803041


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