Cosmological Constraints from Galaxy Clusters in the 2500 square-degree SPT-SZ Survey (1603.06522v1)

Abstract: (abridged) We present cosmological constraints obtained from galaxy clusters identified by their Sunyaev-Zel'dovich effect signature in the 2500 square degree South Pole Telescope Sunyaev Zel'dovich survey. We consider the 377 cluster candidates identified at z>0.25 with a detection significance greater than five, corresponding to the 95% purity threshold for the survey. We compute constraints on cosmological models using the measured cluster abundance as a function of mass and redshift. We include additional constraints from multi-wavelength observations, including Chandra X-ray data for 82 clusters and a weak lensing-based prior on the normalization of the mass-observable scaling relations. Assuming a LCDM cosmology, where the species-summed neutrino mass has the minimum allowed value (mnu = 0.06 eV) from neutrino oscillation experiments, we combine the cluster data with a prior on H0 and find sigma_8 = 0.797+-0.031 and Omega_m = 0.289+-0.042, with the parameter combination sigma_8(Omega_m/0.27)^0.3 = 0.784+-0.039. These results are in good agreement with constraints from the CMB from SPT, WMAP, and Planck, as well as with constraints from other cluster datasets. Adding mnu as a free parameter, we find mnu = 0.14+-0.08 eV when combining the SPT cluster data with Planck CMB data and BAO data, consistent with the minimum allowed value. Finally, we consider a cosmology where mnu and N_eff are fixed to the LCDM values, but the dark energy equation of state parameter w is free. Using the SPT cluster data in combination with an H0 prior, we measure w = -1.28+-0.31, a constraint consistent with the LCDM cosmological model and derived from the combination of growth of structure and geometry. When combined with primarily geometrical constraints from Planck CMB, H0, BAO and SNe, adding the SPT cluster data improves the w constraint from the geometrical data alone by 14%, to w = -1.023+-0.042.

Cosmological Constraints from Galaxy Clusters in the 2500 Square-Degree SPT-SZ Survey

The paper in focus presents a comprehensive analysis of cosmological parameters derived from galaxy clusters. These clusters were identified using the Sunyaev-Zel’dovich (SZ) effect within the 2500 square degree South Pole Telescope Sunyaev-Zel’dovich (SPT-SZ) survey. The researchers utilized data from 377 cluster candidates with redshifts greater than 0.25, ensuring a high detection significance to maintain a 95% purity threshold. The primary aim was to constrain cosmological models by examining cluster abundance as a function of mass and redshift.

A significant aspect of the analysis involved combining SZ data with multi-wavelength observations, particularly using Chandra X-ray data for 82 clusters. Furthermore, a weak lensing-based prior was applied to the normalization of mass-observable scaling relations. To efficiently address the inherent scatter in mass proxies and their correlation, the researchers advanced a numerical technique to compute cluster likelihoods.

Assuming a spatially flat ΛCDM cosmology with a neutrino mass sum of 0.06 eV, the paper found the derived parameter value σ₈ = 0.784 ± 0.039 and Ω_m = 0.289 ± 0.042. These results were consistent with constraints from other cosmological probes like the Cosmic Microwave Background (CMB) measured by SPT, WMAP, and Planck data.

Exploring beyond the standard ΛCDM model, the paper considered the inclusion of neutrino masses as a free parameter and found it to be σ_m = 0.14 ± 0.08 eV with combined data from SPT clusters, Planck CMB, and Baryon Acoustic Oscillation (BAO) data. Additionally, when allowing variations in the effective number of relativistic species (N_eff), they reported N_eff = 3.28 ± 0.20 with σ_m = 0.18 ± 0.09 eV. These findings suggest a potential deviation from the standard model predictions, though within acceptable ranges.

Considering a wCDM cosmology where the dark energy equation of state parameter (w) is free, the SPT cluster data, when combined with Planck CMB, H₀, BAO, and Supernovae data, improved the constraint on w to -1.023 ± 0.042. This marks a 14% enhancement over geometrical data alone.

The paper underscores the efficacy of using SZ cluster surveys for constraining cosmological parameters, especially by leveraging the unique capability of SZ data to select clusters regardless of redshift. This ability offers vital insights into the properties of dark energy and structure growth across cosmic timescales.

Future prospects discussed in the paper include potential integration with weak lensing data directly from SPT-SZ clusters to refine mass scale constraints. Such enhancements could significantly reduce systematic uncertainties, thus providing more stringent tests for extensions to the standard cosmological model, especially concerning dark energy dynamics and neutrino properties.

The findings position the SPT-SZ survey as a formidable instrument in cosmological analyses, both via standalone observational datasets and in complement with other probes, thereby contributing crucially to our understanding of the universe's evolution.