用于BAO径向测量的Photo-z优化
Photo-z optimization for measurements of the BAO radial direction
摘要：
径向方向的重子声学振荡（BAO）提供了一种直接测量宇宙膨胀历史的方法，并在与角BAO信号结合时对空间曲率进行限制。除了光谱测量外，径向BAO还可以通过窄带滤光片获得的足够精确的光度红移来测量。我们探讨了光度测量的要求，使用发光红Galerkin（LRG）竞争性地测量径向BAO信号，并讨论了这种方法可能的系统误差。如果LRG是一个高度均匀的人口，我们表明，光z精度不会大幅提高，通过增加过滤器的数量超过$\sim 10$，除了一小部分的源检测到高信噪比，和宽带过滤器将足以实现测量径向BAO的目标$σ_z = 0.003 (1+z)$。利用SDSS获得的LRG光谱，我们发现LRG的光谱可变性基本上与可获得的光度红移误差成正比，最佳系统由宽度为$Δλ/ λ\sim 0.02$的$\sim$ 30滤光片组成。$S/N > 20$通常需要位于$Hα$断裂处红色一侧的滤光片上，以达到目标光度精度。我们估计，5年的调查，在一个专用的望远镜光学扩展量超过60 ${\rm m}^2 {\rm deg}^2$将是必要的，以获得足够高的星系密度，以足够低的散粒噪声高达$z= 0.85$测量径向BAO。我们的结论是，光谱调查有一个优越的性能比光度的测量BAO在径向方向。
英文摘要：
Baryon Acoustic Oscillations (BAO) in the radial direction offer a method to directly measure the Universe expansion history, and to set limits to space curvature when combined to the angular BAO signal. In addition to spectroscopic surveys, radial BAO might be measured from accurate enough photometric redshifts obtained with narrow-band filters. We explore the requirements for a photometric survey using Luminous Red Galaxies (LRG) to competitively measure the radial BAO signal and discuss the possible systematic errors of this approach. If LRG were a highly homogeneous population, we show that the photo-z accuracy would not substantially improve by increasing the number of filters beyond $\sim 10$, except for a small fraction of the sources detected at high signal-to-noise, and broad-band filters would suffice to achieve the target $σ_z = 0.003 (1+z)$ for measuring radial BAO. Using the LRG spectra obtained from SDSS, we find that the spectral variability of LRG substantially worsens the achievable photometric redshift errors, and that the optimal system consists of $\sim$ 30 filters of width $Δλ/ λ\sim 0.02$. A $S/N > 20$ is generally necessary at the filters on the red side of the $Hα$ break to reach the target photometric accuracy. We estimate that a 5-year survey in a dedicated telescope with etendue in excess of 60 ${\rm m}^2 {\rm deg}^2$ would be necessary to obtain a high enough density of galaxies to measure radial BAO with sufficiently low shot noise up to $z= 0.85$. We conclude that spectroscopic surveys have a superior performance than photometric ones for measuring BAO in the radial direction.
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