First detection of the GI-type of intrinsic alignments of galaxies using the self-calibration method in a photometric galaxy survey

Abstract

Weak gravitational lensing is one of the most promising cosmological probes to constrain dark matter, dark energy, and the nature of gravity at cosmic scales. Intrinsic alignments (IAs) of galaxies have been recognized as one of the most serious systematic effects facing gravitational lensing. Such alignments must be isolated and removed to obtain a pure lensing signal. Furthermore, the alignments are related to the processes of galaxy formation, so their extracted signal can help in understanding such formation processes and improving their theoretical modeling. We report in this Letter the first detection of the gravitational shear--intrinsic shape (GI) correlation and the intrinsic shape--galaxy density (Ig) correlation using the self-calibration method in a photometric redshift survey. These direct measurements are made from the KiDS-450 photometric galaxy survey with a significance of 3.65$\sigma$ in the third bin for the Ig correlation, and 3.51$\sigma$ for the GI cross-correlation between the third and fourth bins. The self-calibration method uses the information available from photometric surveys without needing to specify an IA model and will play an important role in validating IA models and IA mitigation in future surveys such as the Rubin Observatory Legacy Survey of Space and Time, Euclid, and WFIRST.

arXiv comment8 pages, 2 figures

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• Intrinsic and extrinsic correlations of galaxy shapes and sizes in weak lensing data
• Intrinsic alignments of galaxies around cosmic voids
• A rising tide: Intrinsic alignments since the turn of the millennium
• Galaxy Alignments with Surrounding Structure in the Sloan Digital Sky Survey
• A direct detection method of galaxy intrinsic ellipticity-gravitational shear correlation in non-linear regimes using self-calibration
• Non-linear infusion of intrinsic alignment and source clustering: impact on non-Gaussian cosmic shear statistics