CONSTRAINING THE COSMOLOGICAL BARYON DENSITY WITH X-RAY-CLUSTERS

We study the properties of X-ray galaxy clusters in four cold dark mat ter models with different baryon fractions Omega(BM) ranging from 5 to 20 per cent. By using an original three-dimensional hydrodynamic code based on the piecewise parabolic method, we run simulations on a box with a size of 64 h(-1) Mpc and we identify the clusters by selecting the peaks in the X-ray luminosity field. We analyse these mock catalog ues by computing the mass function, the luminosity function, the tempe rature distribution and the luminosity-temperature relation. By compar ing the predictions of the different models to a series of recent obse rvational results, we find that only the models with low baryonic cont ent agree with the data, while models with larger baryon fraction are well outside the 1 sigma error bars. In particular, the analysis of th e luminosity functions, both bolometric and in the energy band [0.5-2] keV, requires Omega(BM) less than or similar to 0.05 when we fix the values h = 0.5 and n = 0.8 for the Hubble parameter and the primordial spectral index, respectively. Moreover we find that, independently of the cosmological scenario, all the considered quantities have very li ttle redshift evolution, particularly between z = 0.5 and 0.