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Astron. Astrophys. 345, 329-362 (1999)


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The mass and luminosity functions of galaxies and their evolution

Patrick Valageas and Richard Schaeffer

Service de Physique Théorique, CEN Saclay, F-91191 Gif-sur-Yvette, France

Received 29 May 1998 / Accepted 18 December 1998

Abstract

We set up a model for the evolution of the galaxy luminosity function, taking advantage of recent work that brought in some better understanding of the mass function for gravitationally condensed objects. We add to this a simple model of star formation that reproduces the behaviour of the Tully-Fisher relation, in order to attach a luminosity to a massive halo with a given velocity dispersion. The physics of cooling of the gravitationally heated baryonic component allows us to distinguish halos that become groups or clusters from those that eventually form galaxies (possibly within the former objects). With our new mass function and our new application of the cooling criteria - which motivated this paper - we get a satisfactory and natural cutoff at the bright end of the luminosity function, the needed flat slope for faint magnitudes and the correct trend in colors (brighter galaxies are redder) within the framework of the hierarchical clustering picture. This infirms earlier claims that the latter was inadequate to reproduce the former observations. We find the velocity dispersion to be a much better parameter than mass or radius to characterize galaxies. This model of the salient features that may describe galaxies allows one to discuss galaxy evolution as a function of redshift, in number as well as in luminosity. We find that bright galaxies form at [FORMULA] from mergers with a rather quiet evolution afterwards, whereas small galaxies are the result of a continuous merging process active up to the present epoch. The transition is found to occur at the observed transition between bright spirals and small dwarf ellipticals or irregulars. The galaxy luminosity was larger in a recent past for bright galaxies, as has been observed in the CFRS survey. This is because the mass of gas in a typical [FORMULA] galaxy such as the Milky Way is a small fraction of the total baryonic mass and thus star formation is already slowing down. The evolution in number, which is quite well controlled in our model, agrees reasonably well with the counts as a function of apparent magnitude. The quasar multiplicity as a function of redshift is also discussed.

Key words: galaxies: evolution – galaxies: formation – galaxies: luminosity function, mass function – galaxies: quasars: general – cosmology: large-scale structure of Universe


© European Southern Observatory (ESO) 1999

Online publication: April 19, 1999

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