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The statistical properties of the ellipticities of galaxy images depend on how galaxies and evolve, and therefore constrain models of galaxy morphology, which are key the removal of the intrinsic alignment contamination of cosmological weak lensing, as well as to the calibration of weak lensing shape measurements. We construct models based on the halo properties of the Millennium Simulation and confront with a sample of 90, 000 galaxies from the COSMOS Survey, covering three in luminosity and redshifts out to z = 2. The ellipticity measurements are for effects of point spread function smearing, spurious image distortions, and noise. Dividing galaxies into early, late, and irregular types, we find that -type galaxies have up to a factor of two lower intrinsic ellipticity dispersion than -type galaxies. None of the samples shows evidence for redshift evolution, while ellipticity dispersion for late-type galaxies scales strongly with absolute magnitude the bright end. The simulation-based models reproduce the main characteristics of intrinsic ellipticity distributions although which model fares best depends on the criteria of the galaxy sample. We observe fewer close-to-circular late-type images in COSMOS than expected for a sample of randomly oriented circular disks and discuss possible explanations for this deficit.
Joachimi et al. (Fri,) studied this question.
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