Constraining the dark energy with galaxy cluster x-ray data

Abstract

The equation of state characterizing the dark energy component is constrained by combining Chandra observations of the x-ray luminosity of galaxy clusters with independent measurements of the baryonic matter density and the latest measurements of the Hubble parameter as given by the HST key project. By assuming a spatially flat scenario driven by a ``quintessence'' component with an equation of state ${p}_{x}=\ensuremath{\omega}{\ensuremath{\rho}}_{x},$ we place the following limits on the cosmological parameters $\ensuremath{\omega}$ and ${\ensuremath{\Omega}}_{\mathrm{m}}:$ (i) $\ensuremath{-}1<~\ensuremath{\omega}<~\ensuremath{-}0.55$ and ${\ensuremath{\Omega}}_{\mathrm{m}}{=0.32}_{\ensuremath{-}0.014}^{+0.027}$ $(1\ensuremath{\sigma})$ if the equation of state of the dark energy is restricted to the interval $\ensuremath{-}1<~\ensuremath{\omega}<0$ (the usual quintessence) and (ii) $\ensuremath{\omega}=\ensuremath{-}{1.29}_{\ensuremath{-}0.792}^{+0.686}$ and ${\ensuremath{\Omega}}_{\mathrm{m}}{=0.31}_{\ensuremath{-}0.034}^{+0.037}$ $(1\ensuremath{\sigma})$ if $\ensuremath{\omega}$ violates the null energy condition and assume values below $\ensuremath{-}1$ (extended quintessence or ``phantom'' energy). These results are in good agreement with independent studies based on supernovae observations, large-scale structure, and the anisotropies of the cosmic background radiation.