Astron. Astrophys. 337, 31-38 (1998)

Cluster luminosity function and nth ranked magnitude as a distance indicator ^{* **}

S. Rauzy ¹, C. Adami ² and A. Mazure <sup>2

1</sup> Centre de Physique Theorique, Marseille, France
² IGRAP, Laboratoire d'Astronomie Spatiale, Marseille, France

Received 20 April 1998 / Accepted 4 June 1998

Abstract

We define here a standard candle to determine the distance of clusters of galaxies and to investigate their peculiar velocities by using the nth rank galaxy (magnitude m_n). We address the question of the universality of the luminosity function for a sample of 28 rich clusters of galaxies (cz20000 km.s^-1) in order to model the influence on m_n of cluster richness. This luminosity function is found to be universal and the fit of a Schechter profile gives =-1.500.11 and in the range [-21,-17]. The uncorrected distance indicator m_n is more efficient for the first ranks n. With n=5, we have a dispersion of 0.61 magnitude for the (m_n,5log(cz)) relation. When we correct for the richness effect and subtract the background galaxies we reduce the uncertainty to 0.21 magnitude with n=15. Simulations show that a large part of this dispersion originates from the intrinsic scatter of the standard candle itself. These provide upper bounds on the amplitude of cluster radial peculiar motions. At a confidence level of 90 , the dispersion is 0.13 magnitude and is limited to 1200 km.s^-1 for our sample of clusters.

Key words: cosmology: distance scale cosmology: large-scale structure of Universe galaxies: clusters galaxies: luminosity function

* Based on observations collected at the European Southern Observatory (La Silla, Chile)
** http://www.astrsp-mrs.fr/www/enacs.html

Send offprint requests to: C. Adami

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Contents

• 1. Introduction
• 2. The sample
• 3. The cluster luminosity function
  • 3.1. The method
  • 3.2. Analysis
    • 3.2.1. Spatial variations
    • 3.2.2. Universality of the LF
    • 3.2.3. Modelisation
• 4. The distance indicator
  • 4.1. Definition of the optimal rank n for the distance determination
  • 4.2. Peculiar velocities
    • 4.2.1. Analysis
• 5. Conclusion
• Acknowledgements
• References

© European Southern Observatory (ESO) 1998

Online publication: August 6, 1998
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