Advertisement

Faint Stars in the Ursa Minor Dwarf Spheroidal Galaxy: Implications for the Stellar IMF

  • Rosemary F. G. Wyse
  • Gerard Gilmore
  • Sofia Feltzing
  • Mark Houdashelt
Part of the Astrophysics and Space Science Library book series (ASSL, volume 255)

Abstract

The stellar Initial Mass Function (IMF) is a crucial ingredient in models of star formation and chemical evolution. Star counts in systems with simple star-formation histories are particularly straightforward to interpret. We present the faint stellar luminosity function in an external galaxy, the Ursa Minor dwarf Spheroidal (dSph). This relatively-nearby companion galaxy to the Milky Way has a stellar population with narrow distributions of age and of metallicity, remarkably similar to that of a classical halo globular cluster, i.e. old and metal-poor. The integrated luminosity of the Ursa Minor dSph is also similar to that of a globular cluster, but its central surface brightness is many orders of magnitude lower. Further, again in contrast to globular clusters, the internal dynamics of the Ursa Minor dSph are apparently dominated by dark matter, with(M/L)v ~ 80(M/L) .Perhaps surprisingly, we determine for the Ursa Minor dSph a stellar luminosity function, and inferred IMF, that is identical, down to our completeness limit of ~0.4M ® to that of the globular clusters of similar age and metallicity. Thus the stellar IMF long ago and far away, in a dark-matter-dominated galaxy, was the same as that in star clusters in the Milky Way.

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

References

  1. 1.
    Baraffe, I., Chabrier, G., Allard, F. & Hauschildt, P. (1997)AI1A 327 1054Google Scholar
  2. 2.
    Burkert, A. & Silk, J. (1997)ApJL 488L55ADSCrossRefGoogle Scholar
  3. 3.
    Dinescu, D.I., Girard, T.&van Altena, W.F. (1999),AJ,117 1792ADSCrossRefGoogle Scholar
  4. 4.
    Elson, R., Tanvir, N., Gilmore, G., Johnson, R.A. & Beaulieu, S. (1999) in: Y.-H. Chu, N. Suntzeff, J. Hesser & D. Bohlender eds., New Views of the Magellanic Clouds, IAU Symposium 190, ASP, San Francisco, in pressGoogle Scholar
  5. 5.
    Feltzing, S., Gilmore, G.&Wyse, R.F.G. (1999)ApJ,516 L17ADSCrossRefGoogle Scholar
  6. 6.
    Gerhard, O.&Spergel, D. (1992)ApiL,389 L9Google Scholar
  7. 7.
    Gilmore, G. & Howell, D. eds.The Stellar Initial Mass FunctionASP conf. series vol 142, ASP, San FranciscoGoogle Scholar
  8. 8.
    Hargreaves, J., Gilmore, G. & Annan, C. (1996)MNRAS 279 108ADSCrossRefGoogle Scholar
  9. 9.
    Hargreaves, J., Gilmore, G., Irwin, M. & Carter, D. (1994)MNRAS 271 693ADSGoogle Scholar
  10. 10.
    Hernandez, X., Gilmore, G.&Valls-Gabaud, D. (1999)MNRAS, in pressGoogle Scholar
  11. 11.
    Klessen, R. & Kroupa, P. (1998)ApJ 498,143ADSCrossRefGoogle Scholar
  12. 12.
    Mateo, M. (1998)ARAA 36 435ADSCrossRefGoogle Scholar
  13. 13.
    Mighell, K. & Burke, C. (1999)Ap 118366Google Scholar
  14. 14.
    Moore, B., Quinn, T., Governato, M., Stadel, T.&Lake, G. (1999)MNRAS, submittedGoogle Scholar
  15. 15.
    Olszewski, E. & Aaronson, M. (1995)AJ 90 2221ADSCrossRefGoogle Scholar
  16. 16.
    Piatek, P.&Pryor, C. (1995)AJ,109,1071ADSCrossRefGoogle Scholar
  17. 17.
    Piotto, G. & Zoccali, M. (1999)A&A 345 845ADSGoogle Scholar
  18. 18.
    Piotto, G., Cool, A.&King, I.R. (1997)AJ,115 1888Google Scholar
  19. 19.
    Smecker-Hane, T.A. & McWilliam, A. (1999) in: I. Hubeny, S. Heap & R. Cornett eds.Spectro-Photometric Dating of Stars and GalaxiesASP, San Francisco, in pressGoogle Scholar
  20. 20.
    Tremaine, S. & Gunn, J.E. (1978)Phys Rev Lett 286 27Google Scholar
  21. 21.
    von Hippel, T., Gilmore, G., Jones, D. & Tanvir, N. (1996)AJ 112 192ADSCrossRefGoogle Scholar
  22. 22.
    Wyse, R.F.G. (1998) in: G. Gilmore G. & D. Howell, eds.The Stellar Initial Mass FunctionASP conf. series vol 142, ASP, San Francisco, p. 89Google Scholar
  23. 23.
    Zoccali, M., Cassisi, S., Frogel, J., Gould, A.et al.(1999) preprintGoogle Scholar

Copyright information

© Springer Science+Business Media Dordrecht 2000

Authors and Affiliations

  • Rosemary F. G. Wyse
    • 1
  • Gerard Gilmore
    • 2
  • Sofia Feltzing
    • 3
  • Mark Houdashelt
    • 4
  1. 1.Physics and Astronomy DepartmentThe Johns Hopkins UniversityBaltimoreUSA
  2. 2.Institute of AstronomyCambridgeEngland
  3. 3.Lund ObservatoryLundSweden
  4. 4.Physics and Astronomy DepartmentThe Johns Hopkins UniversityBaltimoreUSA

Personalised recommendations