理解SKA-LOW 21厘米宇宙学实验中的频谱伪影：电缆反射的影响
Understanding spectral artefacts in SKA-LOW 21-cm cosmology experiments: the impact of cable reflections
AI总结：
本文研究SKA-Low中同轴电缆反射对21厘米宇宙学EoR窗口的污染，通过端到端仿真和散射参数建模表明，即使0.1%的电缆长度公差也会在所有k模式上造成约10%的污染。
摘要：
宇宙黎明以第一批恒星的形成作为标志，并早于再电离纪元（EoR），当时宇宙因这些首批恒星和星系产生的辐射而经历了一次根本性转变。干涉式21厘米实验旨在探测来自这些时期的红移中性氢信号，从而约束早期宇宙的条件。平方公里阵列（SKA）的SKA-Low仪器被设想为在米波和厘米波波段最大且最灵敏的射电望远镜。最新的孔径阵列验证系统采用7米同轴传输线，将低噪声放大器连接到模拟接收链前部的光发射机。这些组件之间的阻抗失配会导致部分反射的电磁信号，从而在仪器带通中引入色差。这会使前景信号的功率出现在更高的延迟处，可能污染“EoR窗口”，即21厘米信号应当可被探测的区域。我们提出了一个面向SKA-Low的端到端仿真流水线，使用一个复合天空模型，该模型结合了来自银河系和河外全天MWA（GLEAM）巡天、Haslam 408 MHz以及由21cmSPACE模拟器生成的1.5 cGpc 21厘米亮温度数据立方体的射电前景。我们根据同轴传输线的规格和体材料特性，推导出其散射参数模型。假设使用长度≤15.0米、阻抗失配≤10 Ω的相同电缆，反射被限制在EoR窗口以下。然而，我们证明，即使0.1%的长度公差也会在所有可访问的k模式上引入绝对分数差异约为10%的污染。
英文摘要：
The Cosmic Dawn was marked by the formation of the first stars, and preceded the Epoch of Reionization (EoR), when the Universe underwent a fundamental transformation caused by the radiation from these first stars and galaxies. Interferometric 21-cm experiments aim to probe redshifted neutral hydrogen signals from these periods, constraining the conditions of the early Universe. The SKA-Low instrument of the Square Kilometre Array (SKA) is envisaged to be the largest and most sensitive radio telescope at metre and centimetre wavelengths. The latest Aperture Array Verification Systems feature 7-m coaxial transmission lines connecting the low noise amplifiers to optical transmitters at the front of the analogue-receiving chain. An impedance mismatch between these components results in a partially reflected electromagnetic signal, introducing chromatic aberrations into the instrument bandpass. This causes power from the foreground signals to appear at higher delays, potentially contaminating the 'EoR window', a region in which the 21-cm signal should be detectable. We present an end-to-end simulation pipeline for SKA-Low using a composite sky model combining radio foregrounds from the Galactic and Extragalactic All-Sky MWA (GLEAM) Survey, Haslam $408\,$MHz, and a 1.5-cGpc 21-cm brightness temperature cube generated with the 21cmSPACE simulator. We derive a model for the scattering parameters of a coaxial transmission line in terms of its specifications and bulk material properties. Assuming identical cables of length $\leq 15.0\,$m with impedance mismatch $\leq 10\, Ω$, the reflection is confined below the EoR window. However, we demonstrate that even a 0.1 per cent length tolerance introduces contamination with an absolute fractional difference of $\sim 10$ per cent across all accessible k-modes.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
