Mitigating the effects of antenna-to-antenna variation on redundant-baseline calibration for 21 cm cosmology
Mitigating the effects of antenna-to-antenna variation on redundant-baseline calibration for 21 cm cosmology
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DOI：
10.1093/mnras/stz1287
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发表时间：
2018-09
影响因子：
4.8
通讯作者：
Naomi Orosz;J. Dillon;A. Ewall-Wice;A. Parsons;N. Thyagarajan
中科院分区：
文献类型：
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作者：
Naomi Orosz;J. Dillon;A. Ewall-Wice;A. Parsons;N. Thyagarajan
从天体物理前景的宇宙学信号的分离是一个根本的挑战，任何努力，以探测在宇宙黎明和时代的再电离（EoR）使用21厘米超精细过渡中性氢的演变。前景分离是可能的，因为它们内在的光谱平滑性，使它们与光谱复杂的宇宙信号区分开来，即使它们比宇宙信号亮5个数量级。精确校准的无线电干涉仪对于保持前景的平滑性和可分离性至关重要。一种强大的校准策略是在具有相同物理间隔的天线对之间使用冗余测量，以便在不参考天空模型的情况下求解每个天线的频谱响应。这一战略正在由氢时代再电离阵列（HERA）采用，这是南非的一个大型射电望远镜，目前正在进行观测，同时正在建造350个14米的碟形天线。然而，任何真实的射电望远镜固有的完全冗余的偏差使校准问题复杂化。使用HERA的模拟，我们展示了如何校准与天线天线的变化，在碟形天线的建设和放置一般会导致光谱结构，否则平滑的前景，显着减少了宇宙模式的数量可用于21厘米的测量。然而，我们也表明，这种影响可以在很大程度上消除了修改后的冗余基线校准策略，主要依赖于短基线。
The separation of cosmological signal from astrophysical foregrounds is a fundamental challenge for any effort to probe the evolution of neutral hydrogen during the Cosmic Dawn and epoch of reionization (EoR) using the 21 cm hyperfine transition. Foreground separation is made possible by their intrinsic spectral smoothness, making them distinguishable from spectrally complex cosmological signal even though they are ~5 orders of magnitude brighter. Precisely calibrated radio interferometers are essential to maintaining the smoothness and thus separability of the foregrounds. One powerful calibration strategy is to use redundant measurements between pairs of antennas with the same physical separation in order to solve for each antenna's spectral response without reference to a sky model. This strategy is being employed by the Hydrogen Epoch of Reionization Array (HERA), a large radio telescope in South Africa that is now observing while being built out to 350 14-m dishes. However, the deviations from perfect redundancy inherent in any real radio telescope complicate the calibration problem. Using simulations of HERA, we show how calibration with antenna-to-antenna variations in dish construction and placement generally lead to spectral structure in otherwise smooth foregrounds that significantly reduces the number of cosmological modes available to a 21 cm measurement. However, we also show that this effect can be largely eliminated by a modified redundant-baseline calibration strategy that relies predominantly on short baselines.