SIMBAD references

We present forecasts for constraints on deviations from Gaussian distribution of primordial density perturbations from future high-sensitivity X-ray surveys of galaxy clusters. Our analysis is based on computing the Fisher matrix for number counts and large-scale power spectrum of clusters. The surveys that we consider have high sensitivity and wide area to detect about 2.5 x10⁵ extended sources, and to provide reliable measurements of robust mass proxies for about 2x10⁴ clusters. Based on the so-called self-calibration approach, and including Planck priors in our analysis, we constrain at once nine cosmological parameters and four nuisance parameters, which define the relation between cluster mass and X-ray flux. Because of the scale dependence of large-scale bias induced by local-shape non-Gaussianity, we find that the power spectrum provides strong constraints on the non-Gaussianity f_NLparameter, which complement the stringent constraints on the power spectrum normalization, σ₈, from the number counts. To quantify the joint constraints on the two parameters, σ₈ and f_NL, that specify the timing of structure formation for a fixed background expansion, we define the figure of merit. We find that our surveys constrain deviations from Gaussianity with a precision of Δf_NL ≃ 10 at 1σ confidence level, with FoM_SFT ≃ 39. We point out that constraints on f_NL are weakly sensitive to the uncertainties in the knowledge of the nuisance parameters. As an application of non-Gaussian constraints from available data, we analyse the impact of positive skewness on the occurrence of XMMU-J2235, a massive distant cluster recently discovered at z ≃ 1.4. We confirm that in a WMAP-7 Gaussian ΛCDM cosmology, within the survey volume, ≃ 5x10^–3 objects like this are expected to be found. To increase the probability of finding such a cluster by a factor of at least 10, one needs to evade either the available constraints on f_NLor on the power-spectrum normalization σ₈.