Intrinsic galaxy alignments from the 2SLAQ and SDSS surveys: luminosity and redshift scalings and implications for weak lensing surveys
Intrinsic galaxy alignments from the 2SLAQ and SDSS surveys: luminosity and redshift scalings and implications for weak lensing surveys
复制标题
DOI：
10.1111/j.1365-2966.2007.12312.x
复制
发表时间：
2007-01
影响因子：
4.8
通讯作者：
C. Hirata;R. Mandelbaum;M. Ishak;U. Seljak;R. Nichol;K. Pimbblet;N. Ross;D. Wake
中科院分区：
文献类型：
--
作者：
C. Hirata;R. Mandelbaum;M. Ishak;U. Seljak;R. Nichol;K. Pimbblet;N. Ross;D. Wake
在斯隆数字巡天（SDSS）数据中，在明亮星系的低红移下，大尺度的固有剪切和密度场之间的相关性（宇宙剪切巡天的潜在重要污染物）已被可靠地检测到。在这里，我们对这种效应进行了更详细的描述，它可能导致引力透镜剪切和固有椭圆率（GI相关性）之间的反相关。该测量使用来自 SDSS 光谱样本的 36 278 个发光红色星系 (LRG)，对 SDSS LRG 样本中所有星系子样本的大尺度（高达 60 h−1 Mpc）的影响进行 0.15 3σ 检测；对于 2SLAQ 样本，我们发现对明亮子样本的 2σ 检测，对较暗子样本没有检测。提供了拟合公式，用于缩放 GI 与光度、横向间隔和红移的相关性（2SLAQ 样本虽然很小，但由于其红移基线较长，因此提供了关键的约束）。我们根据 GI 相关性对星系特性的拟合依赖性，估计未来宇宙剪切勘测中 σ8 测量中的污染。我们发现，对于使用所有星系到 R = 24 深度、尺度 l ≈ 500 的玩具宇宙剪切勘测，功率谱的污染范围为 -1.5%（乐观）到 -33%（悲观），尽管预测污染的中心值为 -6.5%。这对应于 σ8 的偏差 Δσ8 = -0.004（乐观）、-0.02（中心）或 -0.10（悲观）。我们提供了在宇宙学参数估计代码中包含此误差的方案。主要的不确定性在于 L ≤ L 蓝色星系的处理，我们没有检测到 GI 信号，但如果它们的 GI 幅度接近我们的上限，则它们可能主导 GI 污染。这些星系潮汐排列的特征，特别是与宇宙剪切相关的红移，应该是宇宙剪切界的高度优先事项。
Correlations between intrinsic shear and the density field on large scales, a potentially important contaminant for cosmic shear surveys, have been robustly detected at low redshifts with bright galaxies in Sloan Digital Sky Survey (SDSS) data. Here we present a more detailed characterization of this effect, which can cause anticorrelations between gravitational lensing shear and intrinsic ellipticity (GI correlations). This measurement uses 36 278 luminous red galaxies (LRGs) from the SDSS spectroscopic sample with 0.15 3σ detections of the effect on large scales (up to 60 h−1 Mpc) for all galaxy subsamples within the SDSS LRG sample; for the 2SLAQ sample, we find a 2σ detection for a bright subsample, and no detection for a fainter subsample. Fitting formulae are provided for the scaling of the GI correlations with luminosity, transverse separation and redshift (for which the 2SLAQ sample, while small, provides crucial constraints due to its longer baseline in redshift). We estimate contamination in the measurement of σ8 for future cosmic shear surveys on the basis of the fitted dependence of GI correlations on galaxy properties. We find contamination to the power spectrum ranging from −1.5 per cent (optimistic) to −33 per cent (pessimistic) for a toy cosmic shear survey using all galaxies to a depth of R = 24 using scales l ≈ 500, though the central value of predicted contamination is −6.5 per cent. This corresponds to a bias in σ8 of Δσ8 = −0.004 (optimistic), −0.02 (central) or −0.10 (pessimistic). We provide a prescription for inclusion of this error in cosmological parameter estimation codes. The principal uncertainty is in the treatment of the L ≤ L blue galaxies, for which we have no detection of the GI signal, but which could dominate the GI contamination if their GI amplitude is near our upper limits. Characterization of the tidal alignments of these galaxies, especially at redshifts relevant for cosmic shear, should be a high priority for the cosmic shear community.