CFHTLenS: Combined probe cosmological model comparison using 2D weak gravitational lensing (1212.3338v2)

Abstract: We present cosmological constraints from 2D weak gravitational lensing by the large-scale structure in the Canada-France Hawaii Telescope Lensing Survey (CFHTLenS) which spans 154 square degrees in five optical bands. Using accurate photometric redshifts and measured shapes for 4.2 million galaxies between redshifts of 0.2 and 1.3, we compute the 2D cosmic shear correlation function over angular scales ranging between 0.8 and 350 arcmin. Using non-linear models of the dark-matter power spectrum, we constrain cosmological parameters by exploring the parameter space with Population Monte Carlo sampling. The best constraints from lensing alone are obtained for the small-scale density-fluctuations amplitude sigma_8 scaled with the total matter density Omega_m. For a flat LambdaCDM model we obtain sigma_8(Omega_m/0.27)^0.6 = 0.79+-0.03. We combine the CFHTLenS data with WMAP7, BOSS and an HST distance-ladder prior on the Hubble constant to get joint constraints. For a flat LambdaCDM model, we find Omega_m = 0.283+-0.010 and sigma_8 = 0.813+-0.014. In the case of a curved wCDM universe, we obtain Omega_m = 0.27+-0.03, sigma_8 = 0.83+-0.04, w_0 = -1.10+-0.15 and Omega_K = 0.006+0.006-0.004. We calculate the Bayesian evidence to compare flat and curved LambdaCDM and dark-energy CDM models. From the combination of all four probes, we find models with curvature to be at moderately disfavoured with respect to the flat case. A simple dark-energy model is indistinguishable from LambdaCDM. Our results therefore do not necessitate any deviations from the standard cosmological model.

• The paper demonstrates that CFHTLenS 2D weak lensing data alone constrain σ8(Ωm/0.27)^0.6 = 0.79 ± 0.03, providing robust estimates for a flat ΛCDM model.
• It employs non-linear dark matter power spectrum models and Population Monte Carlo sampling to compare different cosmological models using Bayesian evidence.
• Joint analysis with external datasets (WMAP7, BOSS, HST) refines key parameters and moderately disfavors curved models in favor of ΛCDM consistency.

Essay on "CFHTLenS: Combined Probe Cosmological Model Comparison using 2D Weak Gravitational Lensing"

The paper by Kilbinger et al. provides an extensive analysis of cosmological parameters derived from 2D weak gravitational lensing data obtained from the Canada-France Hawaii Telescope Lensing Survey (CFHTLenS). This survey spans 154 square degrees and captures data over five optical bands, offering a significant dataset composed of measurements from 4.2 million galaxies across redshifts ranging from 0.2 to 1.3. The primary objective of the paper is to extract cosmological constraints by leveraging the 2D cosmic shear correlation functions over various angular scales.

Key Analytical Methods and Models

The analysis employs non-linear dark matter power spectrum models to analyze the lensing data. The authors utilize Population Monte Carlo sampling to probe the parameter space, with a focus on the small-scale density fluctuation amplitude, characterized by $\sigma_8$, and scaled with the total matter density, $\Omega_{m}$. For a flat $\Lambda$CDM model, the paper yields a constraint of $\sigma_8(\Omega_{m}/0.27)^{0.6} = 0.79 \pm 0.03$, a result from lensing data alone.

Additionally, the paper extends its analysis by incorporating joint constraints from CFHTLenS with external data sources such as WMAP7, BOSS, and a Hubble constant prior from HST distance-ladder measurements. The combined probes yield $\Omega_m = 0.283 \pm 0.010$ and $\sigma_8 = 0.813 \pm 0.014$ for a flat $\Lambda$CDM model. In a similar assessment for a curved $w$CDM universe, the derived parameters include $\Omega_m = 0.27 \pm 0.03$, $\sigma_8 = 0.83 \pm 0.04$, $w_0 = -1.10 \pm 0.15$, and $\Omega_K=0.006^{+0.006}_{-0.004}$.

Implications and Model Comparison

The Bayesian evidence approach is applied to compare the likelihood of different cosmological models given the data. Notably, models allowing curvature are found to be moderately disfavored when compared to a flat $\Lambda$CDM model. A simple dark-energy model appears indistinguishable from the standard $\Lambda$CDM, suggesting that the current dataset does not necessitate deviations from the established cosmological model.

Technological and Practical Considerations

A critical aspect of this research is the intricate methodological improvements made over previous analyses, notably T0003. These include enhancements in the CFHTLS data processing pipeline and precise photometric redshift measurements. The accuracy and reliability of the photometric redshifts are ensured through thorough verification techniques, which are essential for the subsequent cosmological parameter estimation. The paper emphasizes the robustness of weak lensing as a diagnostic tool that does not rely on the galaxy-dark matter bias, making it a potent instrument in cosmological research.

Future Directions

While the current analysis solidifies our understanding of key cosmological parameters using 2D weak lensing data, it opens paths for future research leveraging 3D weak lensing techniques that incorporate redshift information more extensively. This can potentially provide even tighter constraints on dark energy and modified gravity models. Given the methodological improvements demonstrated in this work, ongoing and future lensing surveys can benefit from such refined analytical frameworks.

In conclusion, the paper manifests a comprehensive undertaking in cosmological model testing using weak gravitational lensing and provides substantial contributions toward the validation of the standard cosmological framework. The conclusions and approaches set a solid foundation for further explorations in the era of precision cosmology.