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The Form of Shear Estimator, the Reduced Shear, the Pixelation Effect, and the Photon Noise Jun Zhang, Eiichiro Komatsu (The University of Texas at Austin) Caltech, Sep 27, 2011 arXiv: 1002.3614; 1002.3615; 0901.4781, Astro-ph/0612146.
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Outline: The Form of Shear Estimator (general) The Reduced Shear (general) The Pixelation Effect (specific) The Photon Noise (specific) Summary
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The Form of Shear Estimator STEP I, STEP II, GREAT 08, GREAT 10 ?
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Our Claim
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Reasons Warming Up Exercise
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Reasons
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Reasons Are there ideal/conventional shear estimators existing in convenient forms? ?
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Reasons Coordinate Rotation:
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Reasons
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Reasons
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Reasons
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Reasons Indeed, we only need to consider spin-2 shear estimators because of the following:
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Reasons On spin-2 shear estimators:
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Reasons Scalar Pseudo-Scalar Spin-4
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Reasons On spin-2 shear estimators:
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Reasons Consider a special type of galaxies: (, )
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Reasons
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Reasons
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Reasons
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Reasons
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Reasons Bartelmann & Schneider 2001, Phys. Rept., 340, 291
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Reasons In the Presence of PSF: ? ✗
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Our Claim ✗
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An Alternative Way ✗ ✔
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Ref: Astro-ph/0612146, arXiv: 0901.4781, arXiv: 1002.3614
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An Alternative Way Ref: Astro-ph/0612146, arXiv: 0901.4781, arXiv: 1002.3614
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An Alternative Way Correct for the Point Spread Function; No Assumptions on the Morphologies of the Galaxies or the PSF; Exact & Simple Math; Well Defined Treatment of Background Noise; Accurate to the 2nd Order in Shear/Convergence; Immune to Misidentification of Sources (faint/small galaxies, stars) < 10 -2 seconds/Galaxy S / N per galaxy Increased.
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The Reduced Shear
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If one plans to calibrate the multiplicative factor “a+b κ ”, one should pay attention to its dependence on “ κ ”, which, though, is not known a priori in observations.
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The Reduced Shear Theorem:,
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The Pixelation Effect (specific) Moffat PSFGaussian PSF FWHM of both PSF = 12
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The Pixelation Effect (specific) FWHM (PSF) = 12
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The Photon Noise (specific)
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In fact :
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A Fun Thing to Share
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Summary The Form of Shear Estimator (general) The Reduced Shear (general) The Pixelation Effect (specific) The Photon Noise (specific)
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