[论文解读] Planck 2018 results. III. High Frequency Instrument data processing and frequency maps

Planck Collaboration, N. Aghanim+153 more|arXiv (Cornell University)|Jul 17, 2018

Astrophysics and Cosmic Phenomena参考文献 37被引用 64

一句话总结

本文介绍了普朗克2018年高频率仪器（HFI）数据处理流程，通过端到端模拟、利用宇宙微波背景（CMB）偶极子进行校准优化，以及增强对系统效应（如强度-偏振串扰和响应函数失配）的抑制，显著提升了地图制作的准确性。关键成果是实现了10−4量级的绝对校准精度，并首次基于HFI数据获得对再电离光学深度的稳健测量，使太阳偶极方向的确定精度达到亚角分量，且所有频段的残余系统误差均得到降低。

ABSTRACT

This paper presents the High Frequency Instrument (HFI) data processing procedures for the Planck 2018 release. Major improvements in mapmaking have been achieved since the previous 2015 release. They enabled the first significant measurement of the reionization optical depth parameter using HFI data. This paper presents an extensive analysis of systematic effects, including the use of simulations to facilitate their removal and characterize the residuals. The polarized data, which presented a number of known problems in the 2015 Planck release, are very significantly improved. Calibration, based on the CMB dipole, is now extremely accurate and in the frequency range 100 to 353 GHz reduces intensity-to-polarization leakage caused by calibration mismatch. The Solar dipole direction has been determined in the three lowest HFI frequency channels to within one arc minute, and its amplitude has an absolute uncertainty smaller than $0.35\mu$K, an accuracy of order $10^{-4}$. This is a major legacy from the HFI for future CMB experiments. The removal of bandpass leakage has been improved by extracting the bandpass-mismatch coefficients for each detector as part of the mapmaking process; these values in turn improve the intensity maps. This is a major change in the philosophy of "frequency maps", which are now computed from single detector data, all adjusted to the same average bandpass response for the main foregrounds. Simulations reproduce very well the relative gain calibration of detectors, as well as drifts within a frequency induced by the residuals of the main systematic effect. Using these simulations, we measure and correct the small frequency calibration bias induced by this systematic effect at the $10^{-4}$ level. There is no detectable sign of a residual calibration bias between the first and second acoustic peaks in the CMB channels, at the $10^{-3}$ level.

研究动机与目标

• 通过先进的数据处理和系统误差抑制，提升普朗克HFI频段地图的准确性和可靠性。
• 利用CMB偶极子实现太阳偶极方向的亚角分精度测定和10−4量级的绝对校准精度。
• 通过探测器特定校准和端到端模拟，减少强度-偏振串扰和响应函数失配的影响。
• 通过零检验、交叉功率谱和基于模拟的一致性检验验证数据处理流程。
• 为宇宙学分析（特别是CMB各向异性和再电离研究）提供稳健、高保真的数据产品。

提出的方法

• 采用端到端模拟，对包括ADC非线性响应和热敏电阻漂移在内的仪器系统误差进行建模与校正。
• 实施一种新型地图制作方案（SRoll），对单探测器时间流进行处理，并引入频率相关的带通响应校正。
• 利用CMB偶极子作为主要光度参考，对HFI数据进行校准，实现偶极子振幅绝对不确定度为0.35 µK。
• 在地图制作过程中，为每个探测器提取频率依赖的带通失配系数，以校正光谱响应差异。
• 利用交叉功率谱和零检验（如奇偶环、观测段零检验）验证残余系统误差，并与输入模拟保持一致。
• 应用经验传递函数，校正光束响应中低多极矩的残余效应，降低串扰影响。

实验结果

研究问题

• RQ1 ADC非线性残差对HFI校准的影响如何？能否在10−4量级实现校正？
• RQ2 HFI数据对太阳偶极方向的测定精度如何？其对绝对校准的影响是什么？
• RQ3 带通失配和校准误差在地图中导致的强度-偏振串扰程度有多大？
• RQ4 端到端模拟能否准确再现探测器增益变化和数据中的系统效应？
• RQ5 在不同多极矩（ℓ = 4–5, 100, 2000）下，最终频段地图中的残余系统误差水平如何？

主要发现

• 在HFI三个最低频段中，太阳偶极方向的测定精度达到1角分钟以内，其绝对振幅不确定度低于0.35 µK，实现了10−4量级的校准精度。
• 强度-偏振串扰被降低至ℓ ≈ 100时低于1 × 10−3 µK2，ℓ ≈ 2000时低于5 × 10−2 µK2，主要通过带通失配系数拟合实现。
• 端到端模拟高保真地再现了探测器增益校准和漂移特性，使ADC非线性引起的偏差得以在10−4量级实现校正。
• 在CMB功率谱的前两个声学峰之间未发现可检测的残余校准偏差，其水平低于10−3量级。
• 在ℓ ≈ 2000处，总带通失配串扰估计为5 × 10−2 µK2（353 GHz频段），其中尘埃和CO贡献为主要成分。
• 经验传递函数有效降低了低多极矩残余，使奇偶观测段交叉功率谱中的振荡被抑制至低于1 × 10−5 µK2。