论文标题
光束形成方法是通过无线电阵列望远镜从宇宙黎明中检测21厘米的全局信号
Beamforming approaches toward detecting the 21-cm global signal from Cosmic Dawn with radio array telescopes
论文作者
论文摘要
人们认为，“宇宙黎明”期间的第一批恒星和星系的形成被认为在早期宇宙中从原子氢气中赋予了微弱的信号。从观察上讲，应在仪表波长下的天空平均温度（即全球）温度中的频率依赖性来测量吸收特征。该信号应与平滑的（但更明亮的阶）可分开 - 通过将对数多项式和吸收槽共同拟合到辐射计光谱中。测量全局21-CM信号的大多数方法在偶极样天线上使用辐射计系统。在这里，我们认为基于波束形成的方法可以允许无线电阵列测量全局21-CM信号。我们使用基于Zenith的阵列模拟了50--100 MHz的无线电天空的端到端漂移扫描观察，并发现复杂的侧侧结构引入了显着的频率依赖性系统。但是，频率频率宽度的λ/d演变不会混淆检测。我们得出的结论是，在主梁下方50 dB左右的横梁阵列中，可能会提供一种测量全局21-CM信号的替代方法。使用O（10^5）天线的阵列可以达到此级别。
The formation of the first stars and galaxies during 'Cosmic Dawn' is thought to have imparted a faint signal onto the 21-cm spin temperature from atomic Hydrogen gas in the early Universe. Observationally, an absorption feature should be measurable as a frequency-dependence in the sky-averaged (i.e. global) temperature at meter wavelengths. This signal should be separable from the smooth -- but orders of magnitude brighter -- foregrounds by jointly fitting a log-polynomial and absorption trough to radiometer spectra. A majority of approaches to measure the global 21-cm signal use radiometer systems on dipole-like antennas. Here, we argue that beamforming-based methods may allow radio arrays to measure the global 21-cm signal. We simulate an end-to-end drift-scan observation of the radio sky at 50--100 MHz using a zenith-phased array, and find that the complex sidelobe structure introduces a significant frequency-dependent systematic. However, the λ/D evolution of the beam width with frequency does not confound detection. We conclude that a beamformed array with a median sidelobe level around 50 dB below the main beam may offer an alternative method to measure the global 21-cm signal. This level is achievable by arrays with O(10^5) antennas.
