The Life and Times of SagDeg

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Science  07 Sep 2001:
Vol. 293, Issue 5536, pp. 1733
DOI: 10.1126/science.293.5536.1733c

The Sagittarius dwarf elliptical galaxy (SagDeg) is on a collision course with the Milky Way and in the next few billion years will be tidally disrupted by its larger neighbor. The SagDeg galaxy has had a long history (about 10 billion years) of star formation; however, the details of SagDeg's stellar life are poorly understood.

Using the photometric uniformity and precision of the Two Micron All Sky Survey, Cole has derived a new color-magnitude diagram of about 1400 red giant stars in the center of SagDeg that shows a large spread in the mean metallicity. A larger fraction of high-metallicity-to-low-metallicity stars was found, indicating a longer history of star formation than previously suggested. This enhanced stellar history is also surprising given SagDeg's current lack of gas. It is possible that SagDeg used to be a larger galaxy that is now in the last stages of tidal disruption or that it captured some Milky Way gas on a previous close passage. — LR

Astrophys. J., in press.

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