STEP2 simulated images Richard Massey with Molly Peeples, Will High, Catherine Heymans, etc. etc.

STEP2 simulated imagesSTEP2 simulated images

Richard Massey with

Molly Peeples, Will High, Catherine Heymans, etc. etc.

Shapelets basis functionsShapelets basis functions(an empirical approach)(an empirical approach)

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http://www.astro.caltech.edu/~rjm/shapelets

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STEP2 PSFsSTEP2 PSFs

A motley assortment designed to target several specific problems in shear measurement.

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n =radial oscillations (c.f. QM energy)

n=radial oscillations (c.f. QM energy)

m=rotational oscillations (c.f. QM Lr momn)

• Place real galaxies into parameter space• Smooth parameter space and resample to generate fake simulated galaxies• Shear galaxies by a known amount, then apply PSF and add observational noise.

Refregier et al. (2001)

Obtain galaxies with the same distribution and shape statistics as that from the input population Contain complex morphologies

STEP2 shapelet galaxiesSTEP2 shapelet galaxies

Massey et al. (2003)

• Decompose COSMOS galaxies into representative shapelet components

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c12

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COSMOS first year mosaicHubble Space Telescope • ACS

Example STEP2 imagesExample STEP2 images

Animations show0%-10% shear in 1%

steps.

Real signal is only ~2%.

Real imageSimulated image

QuickTime™ and aVideo decompressor

are needed to see this picture.QuickTime™ and a

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QuickTime™ and aVideo decompressor

are needed to see this picture.QuickTime™ and a

Video decompressorare needed to see this picture.

QuickTime™ and aVideo decompressor

are needed to see this picture.QuickTime™ and a

Video decompressorare needed to see this picture.

• Shapelet method has been extended by Molly Peeples to simulate Subaru i’-band images.• COSMOS ACS F814W galaxies used as a training set.• Plenty of galaxies to keep populations unique without perturbing shapelet coefficients.

Available in input cataloguesAvailable in input catalogues

• Input shear for each image (nb a few images were malformed)

• Object photometry

• Object astrometry

• Object star/galaxy classification

• Unweighted object ellipticity (Q11-Q22,2Q12)/(Q11+Q22)

• Unweighted object rms size2 (Q11+Q22)

Everything quoted before convolution with the PSF.

STEP2 image ingredientsSTEP2 image ingredients

Realise image

Model galaxy morphologyPDF in shapelet space

Morph and resample PDF to generate new galaxies

Apply shear signal

Add observational noise

Measure shear

?

Convolve with PSF

Correlated between adjacent pixels

Very deep, to mimic best future data setsDo shapelets capture extended wings? (Yes)---”--- ---”--- central cusps? (Not as well)

Extreme opposite (pure exponential) to test

NOISEPhoton shot noise plus sky background

GALAXIESCOSMOS training set automatically

incorporates the true cosmology, galaxy morphology distribution (size, mag), etc.

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Specific tests to challenge shear measurement

STARSModelled from real Subaru data,

using shapelets to nmax=8