Constraining the dark energy with galaxy clusters 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 $p_x=\omega {\rho }_x$ we place the following limits on the cosmological parameters $\omega$ and ${\Omega }_{\mathrm{m}}$: (i) $-1\le \omega \le -0.55$ and ${\Omega }_{\mathrm{m}}=0.32_{-0.014}^{+0.027}$ (1$\sigma$) if the equation of state of the dark energy is restricted to the interval $-1\le \omega <0$ (\emph{usual} quintessence) and (ii) $\omega =-1.29_{-0.792}^{+0.686}$ and ${\Omega }_{\mathrm{m}}=0.31_{-0.034}^{+0.037}$ ($1\sigma$) if $\omega$ violates the null energy condition and assume values $<-1$ (\emph{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.

6 pages, 4 figures, LaTeX