Data-constrained reionization and its effects on cosmological parameters

We perform an analysis of the recent WMAP7 data considering physically motivated and viable reionization scenarios with the aim of assessing their effects on cosmological parameter determinations. The main novelties are: (i) the combination of cosmic microwave background data with astrophysical results from quasar absorption line experiments; (ii) the joint variation of both the cosmological and astrophysical [governing the evolution of the free electron fraction xe(z)] parameters. Including a realistic, data-constrained reionization history in the analysis induces appreciable changes in the cosmological parameter values deduced through a standard WMAP7 analysis. Particularly noteworthy are the variations in Ωbh2=0.02258-0.00056+0.00057 [WMAP7 (Sudden)] vs Ωbh2=0.02183±0.00054 [WMAP7+ASTRO (CF)] and the new constraints for the scalar spectral index, for which WMAP7+ASTRO (CF) excludes the Harrison-Zel’dovich value ns=1 at >3σ. Finally, the electron-scattering optical depth value is considerably decreased with respect to the standard WMAP7, i.e. τe=0.080±0.012. We conclude that the inclusion of astrophysical data sets, allowing to robustly constrain the reionization history, in the extraction procedure of cosmological parameters leads to relatively important differences in the final determination of their values.