The Intergalactic Medium as a Cosmological Tool

Abstract

In this talk I will review the capabilities of high-resolution (UVES and Keck) and low resolution (Sloan Digital Sky Survey – SDSS) quasar (QSO) Lyman- α absorption spectra as cosmological tools to probe the dark matter distribution in the high redshift universe. I will first summarize the results in terms of cosmological parameters and then discuss consistency with the parameters derived from other large scale structure observable such as the Cosmic Microwave Background (CMB) and weak lensing surveys. When the Lyman- α forest data are combined with CMB data and the weak lensing results of the z-COSMOS survey the constraints are: σ 8 = 0.800 ± 0.023 , n s = 0.971 ± 0.011 Ω m = 0.247 ± 0.016 (1- σ error bars), in perfect agreement with the CMB results of WMAP year five alone. I will briefly address the importance of Lyman- α for constraining the neutrino mass fraction. Furthermore, I will present constraints on the mass of warm dark matter (WDM) particles derived from the Lyman- α flux power spectrum of 55 high–resolution HIRES Lyman- α forest spectra at 2.0 < z < 6.4 . From the HIRES spectra alone, we obtain a lower limit of m WDM ≳ 1.2 keV (2 σ ) if the WDM consists of early decoupled thermal relics and m WDM ≳ 5.6 keV (2 σ ) for sterile neutrinos. Adding the SDSS Lyman- α flux power spectrum at 2.2 < z < 4.2 , we get m WDM ≳ 4 keV and m WDM ≳ 28 keV (2 σ ) for thermal relics and sterile neutrinos. These results improve previous findings by a factor two and are currently the tightest constraints on the coldness of cold dark matter. Finally, I will discuss: i) recent results for a mixture of cold and warm dark matter and the constraints for sterile neutrinos as dark matter candidates in a physically motivated framework (resonant production); ii) perspectives of cross-correlating the Lyman- α forest with convergence maps of the cosmic microwave background; iii) fitting of the flux probability distribution function.