KiDS+VIKING-450: Cosmic shear tomography with optical+infrared data (1812.06076v2)

Abstract: We present a tomographic cosmic shear analysis of the Kilo-Degree Survey (KiDS) combined with the VISTA Kilo-Degree Infrared Galaxy Survey (VIKING). This is the first time that a full optical to near-infrared data set has been used for a wide-field cosmological weak lensing experiment. This unprecedented data, spanning $450~$deg$^2$, allows us to improve significantly the estimation of photometric redshifts, such that we are able to include robustly higher-redshift sources for the lensing measurement, and - most importantly - solidify our knowledge of the redshift distributions of the sources. Based on a flat $\Lambda$CDM model we find $S_8\equiv\sigma_8\sqrt{\Omega_{\rm m}/0.3}=0.737_{-0.036}^{+0.040}$ in a blind analysis from cosmic shear alone. The tension between KiDS cosmic shear and the Planck-Legacy CMB measurements remains in this systematically more robust analysis, with $S_8$ differing by $2.3\sigma$. This result is insensitive to changes in the priors on nuisance parameters for intrinsic alignment, baryon feedback, and neutrino mass. KiDS shear measurements are calibrated with a new, more realistic set of image simulations and no significant B-modes are detected in the survey, indicating that systematic errors are under control. When calibrating our redshift distributions by assuming the 30-band COSMOS-2015 photometric redshifts are correct (following the Dark Energy Survey and the Hyper Suprime-Cam Survey), we find the tension with Planck is alleviated. The robust determination of source redshift distributions remains one of the most challenging aspects for future cosmic shear surveys.

• The paper pioneers integrating optical and infrared data to enhance photometric redshift accuracy for cosmic shear analysis.
• It employs a blind analysis with updated image simulations to derive an S8 value of 0.737 while revealing a 2.3σ tension with Planck measurements.
• The study highlights the critical role of precise redshift calibration in guiding future high-precision cosmic surveys and model validations.

Cosmic Shear Tomography Using KiDS+VIKING-450 Optical and Infrared Data

The paper "KiDS+VIKING-450: Cosmic shear tomography with optical+infrared data" presents a sophisticated analysis of cosmic shear tomography by leveraging data from the Kilo-Degree Survey (KiDS) combined with the VISTA Kilo-Degree Infrared Galaxy Survey (VIKING). This analysis pioneers the integration of a complete optical-to-infrared dataset for wide-field cosmological weak lensing experiments, allowing for dramatic improvements in photometric redshift estimations. The paper crucially fortifies the understanding of source redshift distributions, which is vital for precise cosmic shear measurements.

Methodology and Results

The authors implemented a blind analysis within the context of a flat ΛCDM model and reported the constraint on the structure growth parameter $$S_8\equiv\sigma_8\sqrt{\Omega_{\rm m}/0.3}=0.737_{-0.036}^{+0.040}$$. Notably, the recorded tension with the Planck-Legacy Cosmic Microwave Background (CMB) measurements highlights a $2.3\sigma$ discrepancy. This tension persists in this methodologically robust analysis, despite comprehensive marginalizations over known systematic uncertainties, including intrinsic alignment, baryon feedback, neutrino mass parameters, error on shear calibration, and calibration of redshift distributions.

The KiDS shear measurements were calibrated using an updated suite of image simulations, ensuring control over systematic errors. The absence of significant B-modes further underscores the integrity of the dataset. When incorporating the 30-band COSMOS-2015 photometric redshifts, the tension with Planck is notably alleviated, spotlighting the critical role of precise redshift distribution determinations in future cosmic surveys.

Implications for Cosmology

The implications of this research are substantial for both practical and theoretical cosmology. On a practical level, the integration of optical and infrared data underlines an enhanced roadmap for future cosmological surveys, potentially guiding the design and data calibration strategies for upcoming high-precision cosmic shear projects. Theoretical implications extend to the robustness checks on the ΛCDM model. The noted tension with Planck data provokes further inquiry, pricking questions about potential systematic biases, the accuracy of existing cosmological models, or the tantalizing possibility of new physics beyond the standard paradigm.

Future Directions

Anticipated developments in AI and machine learning could amplify the effectiveness of data analysis approaches, employing advanced techniques to further constrain systematic uncertainties in cosmic shear measurements. The continued pursuit of broader wavelength coverage and refined calibration methodologies remains a pivotal direction as cosmology aims for precision answers to fundamental questions about the universe's structure and evolution.

Moreover, this paper sets a precedent for enhanced collaborations and data-sharing protocols across significant cosmological surveys, optimizing resources and fostering a more profound collective understanding of cosmic shear phenomena and their cosmological utilities.

In summary, "KiDS+VIKING-450: Cosmic shear tomography with optical+infrared data" elucidates a frontier in cosmic shear analysis by leveraging comprehensive wavelength data, steering the cosmic community toward more precise cosmological parameters while arousing critical evaluations of current models against emerging evidence.