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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)

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Presentation on theme: "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)"— Presentation transcript:

1 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.

2 Outline: The Form of Shear Estimator (general) The Reduced Shear (general) The Pixelation Effect (specific) The Photon Noise (specific) Summary

3 The Form of Shear Estimator STEP I, STEP II, GREAT 08, GREAT 10 ?

4 Our Claim

5

6 ✗ ✔

7 Reasons Warming Up Exercise

8 Reasons

9 Reasons Are there ideal/conventional shear estimators existing in convenient forms? ?

10 Reasons Coordinate Rotation:

11 Reasons

12 Reasons

13 Reasons

14 Reasons Indeed, we only need to consider spin-2 shear estimators because of the following:

15 Reasons On spin-2 shear estimators:

16 Reasons Scalar Pseudo-Scalar Spin-4

17 Reasons On spin-2 shear estimators:

18 Reasons Consider a special type of galaxies: (, )

19 Reasons

20 Reasons

21 Reasons

22 Reasons

23 Reasons Bartelmann & Schneider 2001, Phys. Rept., 340, 291

24 Reasons In the Presence of PSF: ? ✗

25 Our Claim ✗

26 An Alternative Way ✗ ✔

27 ✗ ✔

28 ✗ ✔

29 Ref: Astro-ph/0612146, arXiv: 0901.4781, arXiv: 1002.3614

30 An Alternative Way Ref: Astro-ph/0612146, arXiv: 0901.4781, arXiv: 1002.3614

31 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.

32 The Reduced Shear

33 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.

34 The Reduced Shear Theorem:,

35 The Pixelation Effect (specific) Moffat PSFGaussian PSF FWHM of both PSF = 12

36 The Pixelation Effect (specific) FWHM (PSF) = 12

37 The Photon Noise (specific)

38

39

40 In fact :

41 A Fun Thing to Share

42

43 Summary The Form of Shear Estimator (general) The Reduced Shear (general) The Pixelation Effect (specific) The Photon Noise (specific)

44

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