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 × 105 extended sources, and to provide reliable measurements of robust mass proxies for about 2 × 104 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 fNL parameter, 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 fNL, 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 ΔfNL ~= 10 at 1σ confidence level, with FoMSFT ~= 39. We point out that constraints on fNL 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, ~= 5 × 10-3 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 fNL or on the power-spectrum normalization σ8.
The potential of X-ray cluster surveys to constrain primordial non-Gaussianity.
MATARRESE, SABINO;MOSCARDINI, LAURO;
2010
Abstract
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 × 105 extended sources, and to provide reliable measurements of robust mass proxies for about 2 × 104 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 fNL parameter, 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 fNL, 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 ΔfNL ~= 10 at 1σ confidence level, with FoMSFT ~= 39. We point out that constraints on fNL 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, ~= 5 × 10-3 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 fNL or on the power-spectrum normalization σ8.
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