A Method for Weak Lensing Flexion Analysis by the HOLICs Moment Approach

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Okura, Yuki
Umetsu, Keiichi
Futamase, Toshifumi
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We have developed a method for measuring higher-order weak lensing distortions of faint background galaxies, namely the weak gravitational flexion, by fully extending the Kaiser, Squires & Broadhurst method to include higher-order lensing image characteristics (HOLICs) introduced by Okura, Umetsu, & Futamase. We take into account explicitly the weight function in calculations of noisy shape moments and the effect of higher-order PSF anisotropy, as well as isotropic PSF smearing. Our HOLICs formalism allows accurate measurements of flexion from practical observational data in the presence of non-circular, anisotropic PSF. We test our method using mock observations of simulated galaxy images and actual, ground-based Subaru observations of the massive galaxy cluster A1689 ($z=0.183$). From the high-precision measurements of spin-1 first flexion, we obtain a high-resolution mass map in the central region of A1689. The reconstructed mass map shows a bimodal feature in the central $4'\times 4'$ region of the cluster. The major, pronounced peak is associated with the brightest cluster galaxy and central cluster members, while the secondary mass peak is associated with a local concentration of bright galaxies. The refined, high-resolution mass map of A1689 demonstrates the power of the generalized weak lensing analysis techniques for quantitative and accurate measurements of the weak gravitational lensing signal.
Comment: Accepted for publication in ApJ, 36 pages, including 9 figures and 1 table. A version with higher resolution figures and Full Appendix can be found at http://www.asiaa.sinica.edu.tw/keiichi/OUF2/ouf2008.pdf
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