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Astron. Astrophys. 359, 821-842 (2000)

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Multiplicity functions and X-ray emission of clusters and groups versus galaxies and quasars

P. Valageas and R. Schaeffer

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

Received 17 September 1999 / Accepted 26 April 2000


We use a unified analytical formulation - developed in previous papers - for the multiplicity functions of clusters and galaxies. This method is free from the cloud-in-cloud problem encountered in earlier approaches and well adapted to the description of the non-linear clustering features. It is especially suited to simultane ously describe rich clusters, groups and galaxies, consistently with the hierarchical picture of gravitational clustering, as well as their evolution in time. We find a good agreement with observations for the cluster temperature function and we compare our method with the standard Press-Schechter prescription. We also obtain the main properties of the Sunyaev-Zel'dovich effect (mean and variance). Then, using a simple model for the cluster X-ray luminosity (taking into account entropy considerations), w e obtain the X-ray luminosity distribution of groups and clusters.

Then, using the same formalism we derive the galaxy and quasar multiplicity functions. In particular, we show that the use of the standard Press-Schechter prescription leads to erroneous conclusions at low redshifts while our approach provides a reasonable agreement with observations in a natural fashion because it is able to distinguish galactic halos from groups or clusters. Finally, we derive the contribution of quasars and galaxies to the X-ray counts. Thus, we obtain a global and consistent picture of the X-ray emissions from all structures . In particular, we show that future observations (e.g., from AXAF) could provide interesting information on galaxy evolution. Indeed, they will constrain the importance of a possible hot diffuse gaseous phase in galactic halos and they could reveal massive galaxies which are just being formed, through the X-ray emission of their cooling gas.

Key words: galaxies: clusters: general – galaxies: evolution – galaxies: luminosity function, mass function – galaxies: quasars: general – cosmology: large-scale structure of Universe – cosmology: cosmic microwave background

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© European Southern Observatory (ESO) 2000

Online publication: July 13, 2000