Journal Article

Self-calibration of photometric redshift scatter in weak-lensing surveys

Pengjie Zhang, Ue-Li Pen and Gary Bernstein

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 405, issue 1, pages 359-374
Published in print June 2010 | ISSN: 0035-8711
Published online June 2010 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2010.16445.x
Self-calibration of photometric redshift scatter in weak-lensing surveys

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Photometric redshift (photo-z) errors, especially catastrophic errors, are a major uncertainty for precision weak-lensing cosmology. We find that the shear (galaxy number) density and density–density cross-correlation measurements between photo-z bins, available from the same lensing surveys, contain valuable information for self-calibration of the scattering probabilities between the true redshift and photo-z bins. The self-calibration technique we propose does not rely on cosmological priors nor parameterization of the photo-z probability distribution function, and preserves all of the cosmological information available from shear–shear measurement. We estimate the calibration accuracy through the Fisher matrix formalism. We find that, for advanced lensing surveys such as the planned Stage IV surveys, the rate of photo-z outliers can be determined with statistical uncertainties of 0.01–1 per cent for z < 2 galaxies. Among the several sources of calibration error that we identify and investigate, the galaxy distribution bias is likely the most dominant systematic error, whereby photo-z outliers have different redshift distributions and/or bias than non-outliers from the same bin. This bias affects all photo-z calibration techniques based on correlation measurements. Galaxy bias variations of O(0.1) produce biases in photo-z outlier rates similar to the statistical errors of our method, so this galaxy distribution bias may bias the reconstructed scatters at several-σ level, but is unlikely to completely invalidate the self-calibration technique.

Keywords: gravitational lensing; cosmology: observations; cosmology: theory; large-scale structure of Universe

Journal Article.  13164 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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