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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)
Tru
nca
tion o
f hig
hsp
ati
al fr
equenci
es
http://www.astro.caltech.edu/~rjm/shapelets
0 2 4 6 8NN
MM
8
6
4
2
0
-
2
-
4
-
6
-
8
STEP2 PSFsSTEP2 PSFs
A motley assortment designed to target several specific problems in shear measurement.
m =
rota
tional osc
illati
ons
(c.f
. Q
M L
r m
om
n)
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
c01
c12
c.f. c01
c12
c01
c12
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
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.
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.
( )
Specific tests to challenge shear measurement
STARSModelled from real Subaru data,
using shapelets to nmax=8