X-raying the Cosmic Star Formation Rate

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Using current semi-analytic models of structure and star formation based on hierarchical clustering, we connect the cosmic star formation rate (SFR) to the X-ray emission properties of groups and clusters of galaxies. We show that when the baryons cool down from a hot phase to condense into stars with a SFR flat for z>2, then such hot phase yields deep X-ray source counts (at fluxes F=10⁻¹⁵ erg/cm² s in the energy band 0.5-2 keV) about 5 times larger than in the case of a SFR peaked at z 1.5. We also discuss the effect of the SFR on the shape and evolution of the X-ray L-T relation.