CFHTLenS tomographic weak lensing cosmological parameter constraints: Mitigating the impact of intrinsic galaxy alignments (1303.1808v1)

Abstract: We present a finely-binned tomographic weak lensing analysis of the Canada-France-Hawaii Telescope Lensing Survey, CFHTLenS, mitigating contamination to the signal from the presence of intrinsic galaxy alignments via the simultaneous fit of a cosmological model and an intrinsic alignment model. CFHTLenS spans 154 square degrees in five optical bands, with accurate shear and photometric redshifts for a galaxy sample with a median redshift of zm =0.70. We estimate the 21 sets of cosmic shear correlation functions associated with six redshift bins, each spanning the angular range of 1.5<theta<35 arcmin. We combine this CFHTLenS data with auxiliary cosmological probes: the cosmic microwave background with data from WMAP7, baryon acoustic oscillations with data from BOSS, and a prior on the Hubble constant from the HST distance ladder. This leads to constraints on the normalisation of the matter power spectrum sigma_8 = 0.799 +/- 0.015 and the matter density parameter Omega_m = 0.271 +/- 0.010 for a flat Lambda CDM cosmology. For a flat wCDM cosmology we constrain the dark energy equation of state parameter w = -1.02 +/- 0.09. We also provide constraints for curved Lambda CDM and wCDM cosmologies. We find the intrinsic alignment contamination to be galaxy-type dependent with a significant intrinsic alignment signal found for early-type galaxies, in contrast to the late-type galaxy sample for which the intrinsic alignment signal is found to be consistent with zero.

• The paper demonstrates that simultaneous fitting of cosmological and intrinsic alignment models significantly reduces biases in weak lensing measurements.
• It reports precise constraints with sigma8 = 0.799±0.015 and Omega_m = 0.271±0.010 within a flat ΛCDM framework.
• The study highlights a marked intrinsic alignment signal in early-type galaxies, validating its mitigation approach for future surveys.

Overview of "CFHTLenS: Tomographic Weak Lensing"

The paper by Heymans et al. presents a significant advancement in the paper of cosmological parameter constraints through tomographic weak lensing. Utilizing the Canada-France-Hawaii Telescope Lensing Survey (CFHTLenS), the authors explore the impact of intrinsic galaxy alignments on cosmological measurements and propose a method to mitigate these effects through simultaneous fitting of both a cosmological and an intrinsic alignment model. Notably, this research spans 154 square degrees with multiphase optical bands, providing accurate shear and photometric redshifts for a sample with a median redshift of 0.70.

Numerical Results and Theoretical Implications

The paper meticulously combines CFHTLenS data with external cosmological probes, including WMAP7 data on cosmic microwave background, BOSS baryon acoustic oscillations, and a prior on the Hubble constant from the HST distance ladder. These combinations yield constraints on the normalization of the matter power spectrum and the matter density parameter crucially within the framework of a flat $\Lambda$CDM cosmology. More specifically, the results indicate a robust $\sigma_8 = 0.799 \pm 0.015$ and $\Omega_{\rm m} = 0.271 \pm 0.010$. Additionally, for a flat $w$CDM cosmology, they constrain the dark energy equation of state parameter to $w = -1.02 \pm 0.09$. Such precise constraints significantly enhance our understanding of dark energy and the matter power spectrum.

Intrinsic Alignments and Galaxy Type Dependency

The investigation reveals a nuanced understanding of intrinsic alignment contamination, showing a notable dependency on galaxy type. Specifically, a significant intrinsic alignment signal is observed for early-type galaxies, contrasting with the late-type galaxy sample, for which intrinsic alignment is consistent with zero. This suggests that intrinsic alignments are more pronounced in early-type galaxies, a finding aligned with prior observational analyses.

Practical and Theoretical Implications

From a practical standpoint, the mitigation method proposed in this paper represents a viable path to enhancing cosmological constraints from future weak lensing surveys. The simultaneous model fitting approach reduces biases significantly, allowing for more accurate cosmological inferences even in the presence of complex galaxy alignments. Theoretically, these results contribute to refining models on galaxy formation and evolution, particularly through the lens of weak lensing, offering insights into the underlying processes influencing galaxy morphology and distributions.

Future Developments in AI and Lensing Analysis

As computational techniques and AI technologies evolve, there is potential to further optimize the analysis methods employed in weak lensing studies. Advanced machine learning algorithms could enhance the modeling of intrinsic alignments or aid in the identification of subtle signals within cosmic shear data. Moreover, developments in simulation techniques could further improve the covariance matrix estimates, providing more accurate and less computationally expensive models. The integration of AI into these processes represents an exciting frontier for enhancing both the robustness and efficiency of cosmological analyses.

In conclusion, the authors of this paper deliver a comprehensive paper that not only addresses intrinsic alignment impacts in tomographic weak lensing but also sets a foundation for future research in this pivotal area of cosmology. The rigorous analytical approach, coupled with strong numerical results, underpins the potential of weak lensing as a powerful probe of the universe's structure and evolution.