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
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DOI：
10.1088/0004-637x/699/2/958
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发表时间：
2008-12
期刊：
影响因子：
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通讯作者：
Lei Sun;Z. Fan;C. Tao;J. Kneib;S. Jouvel;A. Tilquin
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作者：
Lei Sun;Z. Fan;C. Tao;J. Kneib;S. Jouvel;A. Tilquin
我们研究了星系测光红移中的灾难性误差对宇宙学参数估计的影响。我们考虑一个基准调查与九个过滤器集，并进行照片Z测量模拟。发现有1%的zspec = 0.4的星系被误认为是zphot = 3.5。然后我们采用χ2拟合方法和Fisher矩阵的扩展形式来评估由这些灾难性异常值引起的暗能量状态方程参数w 0和wa的偏差。通过比较两种方法的结果，我们验证了从基准五箱层析分析的w 0和wa的估计可以显着偏差。为了最大限度地减少这种偏差的影响，可以采取两种策略：（1）将宇宙剪切分析限制在0.5 < z < 2.5，预计灾难性的红移误差是微不足道的;（2）对3 < zphot < 4的星系进行光谱调查。我们发现，所需的光谱红移的数量标度为Nspec Δ fcata × A，其中fcata = 1%是灾难性红移误差的分数（假设九过滤器测光调查），A是调查区域。对于A = 1000 deg 2，我们发现Nspec分别> 320和860，以便将（w 0，wa）中的联合偏差减小到小于2σ和1σ。这种光谱测量（选项2）将使选项1的优值提高1.5倍，因此非常需要进行这种测量。
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 nine-filter set and perform photo-z measurement simulations. It is found that a fraction of 1% galaxies at zspec ∼ 0.4 is misidentified to be at zphot ∼ 3.5. We then employ both χ2 fitting method and the extension of Fisher matrix formalism to evaluate the bias on the equation of state parameters of dark energy, w0 and wa, induced by those catastrophic outliers. By comparing the results from both methods, we verify that the estimation of w0 and wa from the fiducial five-bin tomographic analyses can be significantly biased. To minimize the impact of this bias, two strategies can be followed: (1) the cosmic shear analysis is restricted to 0.5 < z < 2.5, where catastrophic redshift errors are expected to be insignificant; (2) a spectroscopic survey is conducted for galaxies with 3 < zphot < 4. We find that the number of spectroscopic redshifts needed scales as Nspec ∝ fcata × A, where fcata = 1% is the fraction of catastrophic redshift errors (assuming a nine-filter photometric survey) and A is the survey area. For A = 1000deg2, we find that Nspec > 320 and 860, respectively, in order to reduce the joint bias in (w0, wa) to be smaller than 2σ and 1σ. This spectroscopic survey (option 2) will improve the figure of merit of option 1 by a factor ×1.5 thus making such a survey strongly desirable.