STEP 3: Space-based simulations
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Space-based images generated using Shapelets

The results of the blind analysis of Shapelet simulations of space-based data are now online.

Shapelet space-based simulations can be downloaded from Caltech from thanks to Will High, Richard Massey and Jason Rhodes. Input shears and galaxy catalogues are also available as a tarball file.

These images simulate i-band data taken with roughly 1 ks exposures from SNAP and 2 ks exposures from ACS, and all have the same zero-point magnitude of 19.58. The images have various pixel scales from 0.04" to 0.10", as described in the Readme file. As with the other STEP simulations, the depth, noise properties, and input shear are constant across every image.

A tarball of high resolution PSF images can be downloaded from here. This is in order to solve the issue of pixelisation in the large pixel scale images. The default is to use the low resolution PSF images for your analysis, but you have the option of using both the low and high resolution.

Rules for the analysis

  • All simulations have constant shear and constant PSFs and also have the same set of galaxies.
  • These measures have been taken to speed up the production of the simulations and also to simplify the final comparison analysis. Knowing that the simulations have these properties is however very different to what one would know about a real data set!
  • Therefore, please do not use extra information about the properties of each image simulation in your analysis and run your pipelines as you would normally on a set of real data.
  • Anisotropic PSF modeling should be performed on each starfield simulation image . Spatial stability of the PSF across the image should not be assumed.

If the use of these simulations result in a publication, please contact Will High (high[at] to determine how to best acknowledge these simulations.

Last modified 3rd May.
STEP pages maintained by Catherine Heymans: heymans[at]
Questions regarding the Shapelet simulations should be directed to Will High:high[at]