[论文解读] Validation of the Scientific Program for the Dark Energy Spectroscopic Instrument

DESI Collaboration, Adame, A. G.+262 more|arXiv (Cornell University)|Jun 9, 2023

Astronomy and Astrophysical Research被引用 28

一句话总结

本文报道了 DESI 调查验证（SV）活动的结果，包括最终目标选择算法、红移分布、曝光优化，以及对完整的 14,000 deg2 survey 的宇宙学约束预测，以及一个 One-Percent 测试（140 deg2）。

ABSTRACT

The Dark Energy Spectroscopic Instrument (DESI) was designed to conduct a survey covering 14,000 deg$^2$ over five years to constrain the cosmic expansion history through precise measurements of Baryon Acoustic Oscillations (BAO). The scientific program for DESI was evaluated during a five month Survey Validation (SV) campaign before beginning full operations. This program produced deep spectra of tens of thousands of objects from each of the stellar (MWS), bright galaxy (BGS), luminous red galaxy (LRG), emission line galaxy (ELG), and quasar target classes. These SV spectra were used to optimize redshift distributions, characterize exposure times, determine calibration procedures, and assess observational overheads for the five-year program. In this paper, we present the final target selection algorithms, redshift distributions, and projected cosmology constraints resulting from those studies. We also present a `One-Percent survey' conducted at the conclusion of Survey Validation covering 140 deg$^2$ using the final target selection algorithms with exposures of a depth typical of the main survey. The Survey Validation indicates that DESI will be able to complete the full 14,000 deg$^2$ program with spectroscopically-confirmed targets from the MWS, BGS, LRG, ELG, and quasar programs with total sample sizes of 7.2, 13.8, 7.46, 15.7, and 2.87 million, respectively. These samples will allow exploration of the Milky Way halo, clustering on all scales, and BAO measurements with a statistical precision of 0.28% over the redshift interval $z<1.1$, 0.39% over the redshift interval $1.1

研究动机与目标

• 通过五个月的 SV 活动，在全面运营前评估 DESI 科学计划。
• 为 MWS、BGS、LRG、ELG 和类星体目标获取深层光谱，以优化红移分布和观测策略。
• 验证五年计划的校准程序、曝光时间和观测开销。
• 展示 DESI 最终的目标选择算法、红移分布及预测的宇宙学约束。
• 展示在规定的目标样本与精度下完成整个 DESI 调查的可行性。

提出的方法

• 开展五个月的 Survey Validation (SV) 活动，以获取多类目标的深层光谱（MWS、BGS、LRG、ELG、类星体）。
• 利用 SV 光谱优化红移分布和曝光时间。
• 评估五年计划的校准程序和观测开销。
• 最终确定目标选择算法并评估其对红移分布和宇宙学预测的影响。
• 使用最终算法和观测深度执行‘One-Percent survey’（140 deg2），以模拟主调查的性能。

Figure 1: The field centers for the fields designed to test MWS, BGS, LRG, ELG, and quasar selections and spectroscopic performance in the DESI Target Selection Validation program. The light gray regions show the full imaging footprint available from Bok and Mayall imaging while the dark gray region

实验结果

研究问题

• RQ1 DESI 在各目标类（MWS、BGS、LRG、ELG、类星体）的最终目标选择算法是什么？
• RQ2 DESI 五年计划的预计红移分布和样本量是多少？
• RQ3 哪些曝光深度、校准程序和开销可以优化 DESI 的调查效率？
• RQ4 DESI 计划样本可达到的宇宙学约束（BAO 测量）是多少？
• RQ5 一个 140 deg2 的 One-Percent 调查是否能再现主调查的性能并为全天空的期望提供信息？

主要发现

• DESI 将完成完整的 14,000 deg2 计划，来自五类的光谱确认目标：MWS、BGS、LRG、ELG 和类星体，总样本量分别为 7.2、13.8、7.46、15.7 和 2.87 百万。
• BAO 测量和聚类分析预计将达到统计精度：z<1.1 为 0.28%，1.1<z<1.9 为 0.39%，1.9<z<3.5 为 0.46%。
• SV 过程提供了优化的红移分布和曝光策略，支持五年 DESI 计划。
• 校准程序和开销已评估，以确保高效的调查操作。
• 一个 140 deg2 的 One-Percent 调查验证了最终的目标选择和深度，为全面调查的期望提供了依据。

Figure 2: Example of the sky coverage of one DESI tile centered at ( $\alpha$ , $\delta$ ) = (0, 0). The white circles display the individual fiber patrol regions. Left: an image that spans four degrees on a side, illustrating the entire DESI focal plane. Right: the smaller region identified by the