X-Ray Probes of Cosmic Star Formation History

We discuss the imprints left by a cosmological evolution of the starformation rate (SFR) on the evolution of X-ray luminosities Lx of normalgalaxies, using the scheme proposed by White and Ghosh (1998, WG98), whereinthe evolution of Lx of a galaxy is driven by the evolution of its X-ray binarypopulation. As indicated in WG98, the profile of Lx with redshift can bothserve as a diagnostic probe of the SFR profile and constrain evolutionarymodels for X-ray binaries. We report here the first calculation of the expectedevolution of X-ray luminosities of galaxies, updating the WG98 work by using asuite of more recently developed SFR profiles that span the currently plausiblerange. The first Chandra deep imaging results on Lx are beginning to probe theSFR profile of bright spirals: the early results are consistent withpredictions based on current SFR models. Using these new SFR profiles, theresolution of the ``birthrate problem'' of low-mass X-ray binaries (LMXBs) andrecycled, millisecond pulsars (WG98) in terms of an evolving global SFR is morecomplete. We discuss the possible impact of the variations in the SFR profileof individual galaxies and galaxy-types.Comment: 16 pages, 2 Figures, Accepted for publication in ApJ Letter