[Previous] | [Session 4] | [Next]
T.T. Fang, G.L. Bryan, C.R. Canizares (Department of Physics \& Center for Space Research, M.I.T.)
A rising problem in cosmology is the so-called ``missing baryons'' problem: the baryon density predicted by standard nucleosynthesis theory and observed in the Lyman alpha forest is significantly larger than the value obtained from observations of the local universe (see, e.g., Fukugita 1998). One of the possible explanations is that the ``missing baryons'' reside in the outskirts of groups or clusters of galaxies in the form of highly ionized gases at temperatures of T ~106 - 108K. The H-like and He-like ions of the heavy elements (like O, Si, Fe) could produce absorption features - the so-called ``X-ray Forest'' - in the X-ray spectrum of a background quasar (Perna & Loeb 1998, Hellsten 1998).
In this work we give a semi-analytic calculation of the X-ray forest distribution based on the Press-Schechter formalism, following Perna & Loeb (1998). We choose three ions (O VIII, Si XIV and Fe XXV) and calculate the distribution functions, the number of absorbers along the line-of-sight to a distant quasar vs. redshift and column density in a given ion. We find significant differences in the evolution of the distribution functions among three cosmological models - SCDM, OCDM and LCDM. We calculate the probability density functions (PDF) and the cumulative distribution functions (CDF) for both variables and, using Monte Carlo simulations, we simulate the distribution of X-ray absorption lines for random lines of sight. Finally we explore the possibility of detecting the X-ray forest with upcoming X-ray missions.
This work is supported in part by NASA contract NAS 8-38249.
If the author provided an email address or URL for general inquiries,
it is as follows: