Probing dark energy via galaxy cluster outskirts

Understand

We present a Bayesian approach to combine $Planck$ data and the X-ray physical properties of the intracluster medium in the virialization region of a sample of 320 galaxy clusters ($0.056<z<1.24$, $kT>3$ keV) observed with $Chandra$.

• We exploited the high-level of similarity of the emission measure in the cluster outskirts as cosmology proxy.
• The cosmological parameters are thus constrained assuming that the emission measure profiles at different redshift are weakly self-similar, that is their shape is universal, explicitly allowing for temperature and redshift dependence of the gas fraction.
• This cosmological test, in combination with $Planck$+SNIa data, allows us to put a tight constraint on the dark energy models.