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Evidence against Formation of the Stellar Bulge by Mergers Taking Place over a Hubble Time

Published online by Cambridge University Press:  23 September 2016

R.M. Rich
R.M. Rich*
Affiliation:
Department of Astronomy, Columbia, University, New York, NY 10027

Abstract

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Data on abundances and ages of stars in the nuclear bulge of the Galaxy are in conflict with a scenario in which the bulge has been slowly accumulated by mergers of Magellanic Cloud-like systems taking place over a Hubble Time.

I review the abundance distribution of 88 K Giant stars in Baade's window, and show that the distribution is fit by the simple model of chemical evolution unmodified by gas infall. The metal rich stars in the bulge could not have formed in small galaxies of ≈ 1010 solar masses, which do not retain their metal-enriched gas.

Two large surveys of luminous evolved stars in the bulge–the M giant surveys of Blanco, and the carbon star surveys of Azzopardi, Lequeux, and Rebeirot, find no luminous carbon stars or M supergiants which would signify the presence of an intermediate-age population. I present infrared photometry of 33 bulge carbon stars which shows that they are intrinsically faint, confirming the lack of an intermediate age population.

The lack of young turnoff stars in the color-magnitude diagrams of bulge fields by Terndrup and Rich further strengthens the case against a substantial bulge population younger than 5 Gyr.

Type
The Galactic Bulge
Information
Symposium - International Astronomical Union , Volume 136: The Galactic Center , 1989 , pp. 63 - 69
Copyright
Copyright © Kluwer 1989 

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