灾难性测光红移对重子声波振荡和弱引力透镜限制暗能量状态方程参数的影响

Impact of the Catastrophic Photo-z Error on the Dark Energy Equation of State Parameters by the Method of Baryon Acoustic Oscillations and Weak Lensing

研究了存在灾难性测光红移误差时重子声波振荡(Baryon Acoustic Oscillations,BAO)和弱引力透镜(Weak Lensing,WL)的互补效应,以及灾难性测光红移误差对限制暗能量状态方程参数的影响。针对类大口径全天巡视望远镜(Large Synoptic Survey Telescope,LSST)的巡天项目,建构了在z-zph面左上角(UL)和右下角(BR)局域性分布的灾难性测光红移误差模型,并分别针对左上角和右下角的灾难性测光红移,利用费舍尔矩阵(Fisher Matrix)分别估计它们对重子声波振荡、弱引力透镜和联合重子声波振荡+弱引力透镜(BAO+WL)限制暗能量状态方程参数的影响。若拟合模型没有包括实际存在的灾难性测光红移误差,则左上角和右下角的灾难性测光红移造成的偏差并非总是同号的。重子声波振荡受灾难性测光红移误差的影响最小,对于总比例为Ft=0.02的灾难性测光红移,最大的影响也只是左上角和右下角两部分对w0造成的偏差,相对偏差约为30%。但在对弱引力透镜和联合重子声波振荡+弱引力透镜的影响上,通常都有几倍的偏差,因此灾难性测光红移误差的影响不可忽略。另外,关于弱引力透镜对w0的限制,左上角和右下角造成的偏差大小几乎相等,但符号相反,从而导致总体影响反而变得很小。当拟合模型包括灾难性测光红移误差在内后,虽然测光红移误差分布模型多了45个自由度,但在同样大小的训练集的情况下,重子声波振荡和弱引力透镜的互补效应仍然很强。在此条件下,暗能量状态方程参数的误差并没有太大的增加。特别是重子声波振荡的限制结果增加量少于1%。弱引力透镜对w0和wa的限制误差分别增加了14%左右(UL+BR)和6%左右(UL+BR),而联合重子声波振荡+弱引力透镜对w0和wa的限制误差都只增加5%左右(UL+BR)。

The impact of the catastrophic photo-z errors on the constraints of dark energy equation of state （EOS） parameters and the complementarity of baryon acoustic oscillations （BAO） and weak lensing （WL） is studied in this paper. Targeting LSST （Large Synoptic Survey Telescope）-like survey projects, we construct a localized catastrophic photo-z error distribution in the upper-left （UL） and bottom-right （BR） of the z--zph plane. For the two parts of the catastrophic distribution, we use Fisher matrix to forecast the impact on dark energy EOS parameter constraints by the methods of BAO, WL and joint BAO and WL （BAO＋WL）. If the existing catastrophic photo-z errors are not included in the fitting model, systematic biases on EOS parameters could be presented. The constraints from UL and BR do not always have the same sign. BAO suffers the least from catastrophic photo-z errors. For total fraction of catastrophic outliers Ft = 0. 02, the biggest bias is on w0 for BAO （UL＋BR） which is about 30% statistical error. But for WL or BAO＋WL, biases are always several times the statistical errors, which shows that the Ft = 0. 02 catastrophic photo-z errors can not be ignored. Moreover, the impacts of UL and BR on w0 for WL are almost the same magnitude but different signs, which reduces the total impact. With the Ft = 0. 02 catastrophic photo-z errors included in the fitting model, the complementarity of BAO and WL is still very strong even though 45 degree of freedom are added into the photo-z error distribution model. Under this condition, the errors of EOS parameters do not increase much. In particular, the errors of EOS parameter from BAO increase by less than one percent compared to that without catastrophic photo-z errors. The errors of w0 and wa from WL increase by approximately 14 percent （UL ＋ BR） and 6 percent （UL ＋ BR）, respectively. For BAO＋WL, the errors of w0 and wa both increase about 5 percent （UL＋BR）.