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

Abstract

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-z 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% 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. As a result, 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 biasmore » the reconstructed scatters at several-σ level, but is unlikely to completely invalidate the self-calibration technique.« less

Authors:

Zhang, Pengjie ^[1]; Pen, Ue -Li ^[2]; Bernstein, Gary ^[3]

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+ Show Author Affiliations

1. Shanghai Astronomical Observatory, Shanghai (China)
2. Univ. of Toronto, Toronto, ON (Canada)
3. Univ. of Pennsylvania, Philadelphia, PA (United States)

Publication Date:

Fri Jun 11 00:00:00 EDT 2010

Research Org.:

Univ. of Pennsylvania, Philadelphia, PA (United States)

Sponsoring Org.:

USDOE Office of Science (SC), High Energy Physics (HEP)

OSTI Identifier:

1203599

Grant/Contract Number:  

FG02-95ER40893

Resource Type:

Accepted Manuscript

Journal Name:

Monthly Notices of the Royal Astronomical Society

Additional Journal Information:

Journal Name: Monthly Notices of the Royal Astronomical Society; Journal ID: ISSN 0035-8711

Publisher:

Royal Astronomical Society

Country of Publication:

United States

Language:

English

Subject:

79 ASTRONOMY AND ASTROPHYSICS; precision weak lensing cosmology; large-scale structure of universe; gravitational lensing; theory; observations