Astron. Astrophys. 358, 471-480 (2000)

The elliptical galaxy formerly known as the Local Group: merging the globular cluster systems

Duncan A. Forbes ^1,2, Karen L. Masters ¹, Dante Minniti ³ and Pauline Barmby <sup>4

1</sup> University of Birmingham, School of Physics and Astronomy, Edgbaston, Birmingham B15 2TT, UK
² Swinburne University of Technology, Astrophysics and Supercomputing, Hawthorn, Victoria 3122, Australia
³ P. Universidad Católica, Departamento de Astronomía y Astrofísica, Casilla 104, Santiago 22, Chile
⁴ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA

Received 5 November 1999 / Accepted 27 January 2000

Abstract

Prompted by a new catalogue of M31 globular clusters, we have collected together individual metallicity values for globular clusters in the Local Group. Although we briefly describe the globular cluster systems of the individual Local Group galaxies, the main thrust of our paper is to examine the collective properties. In this way we are simulating the dissipationless merger of the Local Group, into presumably an elliptical galaxy. Such a merger is dominated by the Milky Way and M31, which appear to be fairly typical examples of globular cluster systems of spiral galaxies.

The Local Group `Elliptical' has about 700 125 globular clusters, with a luminosity function resembling the `universal' one. The metallicity distribution has peaks at [Fe/H] -1.55 and -0.64 with a metal-poor to metal-rich ratio of 2.5:1. The specific frequency of the Local Group Elliptical is initially about 1 but rises to about 3, when the young stellar populations fade and the galaxy resembles an old elliptical. The metallicity distribution and stellar population corrected specific frequency are similar to that of some known early type galaxies. Based on our results, we briefly speculate on the origin of globular cluster systems in galaxies.

Key words: galaxies: formation Galaxy: halo galaxies: star clusters cosmology: observations cosmology: early Universe

Send offprint requests to: D.A. Forbes

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Contents

• 1. Introduction
• 2. The Local Group of galaxies
• 3. Globular clusters of the Local Group
  • 3.1. Luminosities
  • 3.2. Metallicities
  • 3.3. The Milky Way
  • 3.4. M31
  • 3.5. NGC 205
  • 3.6. M33
  • 3.7. The Large Magellanic Cloud
  • 3.8. The Small Magellanic Cloud
  • 3.9. Sagittarius
  • 3.10. Fornax, NGC 147 and NGC 185
  • 3.11. WLM, NGC 6822 and Aquarius
  • 3.12. Galaxies with no globular cluster system
• 4. Properties of the Local Group `Elliptical'
• 5. Spectroscopic metallicities for globular clusters in elliptical galaxies
• 6. Concluding remarks
• Acknowledgements
• References

© European Southern Observatory (ESO) 2000

Online publication: June 8, 2000
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