Effect of Photometric Redshift Uncertainties on Weak Lensing Tomography

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  • 24 June 2005
Abstract
We perform a general analysis of the effects of photometric redshift uncertainties on weak lensing tomography. We describe the photo-z distribution with a bias and Gaussian scatter that are allowed to vary arbitrarily in redshift. We find that both the bias and the scatter are important, and for a fiducial next-generation survey each would need to be known to better than about 0.003-0.01 in each dz=0.1 bin in order to lead to less than a factor of 1.5 increase in the dark energy parameter errors. The more stringent requirement correspond to a larger dark energy parameter space, when redshift variation in the equation of state of dark energy is allowed. Of order 10^4-10^5 galaxies with spectroscopic redshifts will be needed to achieve this level of calibration. These requirements increase in stringency for more ambitious surveys; we quantify such scalings with a convenient fitting formula. No single aspect of a photometrically binned selection of galaxies such as their mean or median suffices, indicating that dark energy parameter determinations are sensitive to the shape and nature of outliers in the photo-z redshift distribution.

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