论文标题
使用Murchison Wideffield阵列,从回报时期的21〜cm信号的多频角功率谱
Multi-frequency angular power spectrum of the 21~cm signal from the Epoch of Reionisation using the Murchison Widefield Array
论文作者
论文摘要
多频角功率谱(MAP)是球形平均功率谱的替代方案,并且在无需视线光谱变换的情况下计算角功率光谱中的局部波动。测试不同的方法以对前景污染的地图和处理,并与球形平均功率谱和单频角功率谱进行比较。我们将地图应用于$ z = 6.2-7.5 $的110〜小时数据,用于默奇森广场的重新离子化实验时期,以计算21〜cm亮度温度波动的统计功率。在存在明亮的前景的情况下,应用了一个过滤器,以在应用之前删除大规模模式,从而大大降低了由于系统学的地图功率。与模拟的21 〜cm宇宙学信号相对于滤波器后的光谱间隔,图显示了10 $^2 $ -10 $^3 $的对比度为0-厘米的宇宙学信号,这反映了球形平均功率谱的结果。还计算了单频角功率谱。在$ z = 7.5 $和$ l = 200 $时,我们找到了53〜mk $^2 $的角功率,超过了模拟的宇宙信号功率一千倍。残留的光谱结构是校准数据固有的,而不是大规模模式的光谱泄漏,是系统功率偏置的主要来源。与球形平均功率谱相比,单频角功率谱的结果略差,并且在应用光谱滤波器以减少前景后。对其他过滤器的探索可能会改善此结果,并考虑更宽的带宽。
The Multi-frequency Angular Power Spectrum (MAPS) is an alternative to spherically-averaged power spectra, and computes local fluctuations in the angular power spectrum without need for line-of-sight spectral transform. To test different approaches to MAPS and treatment of the foreground contamination, and compare with the spherically-averaged power spectrum, and the single-frequency angular power spectrum. We apply the MAPS to 110~hours of data in $z=6.2-7.5$ obtained for the Murchison Widefield Array Epoch of Reionisation experiment to compute the statistical power of 21~cm brightness temperature fluctuations. In the presence of bright foregrounds, a filter is applied to remove large-scale modes prior to MAPS application, significantly reducing MAPS power due to systematics. The MAPS shows a contrast of 10$^2$--10$^3$ to a simulated 21~cm cosmological signal for spectral separations of 0--4~MHz after application of the filter, reflecting results for the spherically-averaged power spectrum. The single-frequency angular power spectrum is also computed. At $z=7.5$ and $l=200$, we find an angular power of 53~mK$^2$, exceeding a simulated cosmological signal power by a factor of one thousand. Residual spectral structure, inherent to the calibrated data, and not spectral leakage from large-scale modes, is the dominant source of systematic power bias. The single-frequency angular power spectrum yields slightly poorer results compared with the spherically-averaged power spectrum, having applied a spectral filter to reduce foregrounds. Exploration of other filters may improve this result, along with consideration of wider bandwidths.