Catastrophic Photo-z Errors and the Dark Energy Parameter Estimates with Cosmic Shear

Details Catastrophic Photo-z Errors and the Dark Energy Parameter Estimates with Cosmic Shear Catastrophic Photo-z Errors and the Dark Energy Parameter Estimates with Cosmic Shear

2008-12-30

arxiv.org/abs/0812.5083v3

ApJ 699,958-967,2009

Astronomy and Astrophysics

Astrophysics

25 pages, 9 figures. Revised version, as accepted for publication in ApJ

Scientific paper

10.1088/0004-637X/699/2/958

We study the impact of catastrophic errors occurring in the photometric redshifts of galaxies on cosmological parameter estimates with cosmic shear tomography. We consider a fiducial survey with 9-filter set and perform photo-z measurement simulations. It is found that a fraction of 1% galaxies at z_{spec}~0.4 is misidentified to be at z_{phot}~3.5. We then employ both chi^2 fitting method and the extension of Fisher matrix formalism to evaluate the bias on the equation of state parameters of dark energy, w_0 and w_a, induced by those catastrophic outliers. By comparing the results from both methods, we verify that the estimation of w_0 and w_a from the fiducial 5-bin tomographic analyses can be significantly biased. To minimize the impact of this bias, two strategies can be followed: (A) the cosmic shear analysis is restricted to 0.5320 and 860 respectively in order to reduce the joint bias in (w_0,w_a) to be smaller than 2\sigma and 1\sigma. This spectroscopic survey (option B) will improve the Figure of Merit of option A by a factor \times 1.5 thus making such a survey strongly desirable.

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