Constraining the Cosmological Baryon Density with X--ray clusters

We study the properties of X-ray galaxy clusters in four cold dark matter 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 64h^-1 Mpc and we identify the clusters by selecting the peaks in the X-ray luminosity field. We analyse these mock catalogues by computing the mass function, the luminosity function, the temperature distribution and the luminosity-temperature relation. By comparing the predictions of the different models to a series of recent observational results, we find that only the models with low baryonic content agree with the data, while models with larger baryon fraction are well outside the 1sigma error bars. In particular, the analysis of the luminosity functions, both bolometric and in the energy band [0.5-2] keV, requires Omega_BM<~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 little redshift evolution, particularly between z=0.5 and 0.