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

Shapelets basis functions (an empirical approach) Truncation of high spatial frequencies N M

STEP2 PSFs A motley assortment designed to target several specific problems in shear measurement.

m =rotational oscillations ( c.f. QM Lr mom n ) n =radial oscillations ( c.f. QM energy) m =rotational oscillations ( c.f. QM Lr mom n ) 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 galaxies Massey et al. (2003) Decompose COSMOS galaxies into representative shapelet components c 01 c 12 c.f. c 01 c 12 c 01 c 12 COSMOS first year mosaic Hubble Space Telescope ACS

Example STEP2 images Animations show 0%-10% shear in 1% steps. Real signal is only ~2%. Real image Simulated image 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.

STEP2 noise model Modelled on real, 40 minute r’ exposures with Subaru Photon shot noise Sky background noise (constant level subtracted) Correlated between adjacent pixels (present in real data due to unresolved background sources and use of DRIZZLE to stack exposures)

Available 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 (Q 11 -Q 22,2Q 12 )/(Q 11 +Q 22 ) Unweighted object rms size 2 (Q 11 +Q 22 ) Everything quoted before convolution with the PSF.

STEP2 image ingredients Realise image Model galaxy morphology PDF 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 sets Do shapelets capture extended wings? (Yes) ---” ”--- central cusps? (Not as well) Extreme opposite (pure exponential) to test NOISE Photon shot noise plus sky background GALAXIES COSMOS training set automatically incorporates the true cosmology, galaxy morphology distribution (size, mag), etc. ( ) Specific tests to challenge shear measurement STARS Modelled from real Subaru data, using shapelets to n max =8