AARTFAAC宇宙探测器：EDGES吸收槽中21厘米功率谱的观测
The AARTFAAC Cosmic Explorer: observations of the 21-cm power spectrum in the EDGES absorption trough
摘要：
EDGES合作报告的21厘米吸收特征比传统天体物理模型预测的要强好几倍。如果是真的，更深的吸收可能会导致21厘米信号在度数尺度上的更强波动（高达1开尔文均方根），使这些波动能够在比以前预测短近50倍的积分时间内被检测到。我们开始了“AARTFAAC宇宙探索者”（ACE）计划，该计划采用AARTFAAC宽视场成像仪，测量或设定在红移范围$z = 17.9-18.6$（$Δν= 72.36-75.09$ ~MHz）中对应于EDGES吸收特征的深部的21厘米波动的功率谱的限制。在这里，我们提出了第一个结果，从两个LST箱：23.5- 23.75小时和23.5- 23.75小时，每个与2小时的数据，记录在'半漂移扫描'模式。我们展示了新的ACE数据处理管道（改编自LOFAR-EoR管道）在AARTFAAC数据上的应用。我们观察到，噪声估计从信道和时间差分斯托克斯~ $V$ vitriles同意彼此。经过2小时的积分和明亮前景的减法，我们获得了在$k = 0.144~h\,\textrm{cMpc}^{-1}$处的$Δ_{21}^2 < (8139~\textrm{mK})^2$和$Δ_{21}^2 < (8549~\textrm{mK})^2$的21厘米功率谱上的两个LST仓的$2σ$上限。对两个LST仓的噪声偏置校正功率谱进行非相干平均，在$k = 0.144~h\,\textrm{cMpc}^{-1}$处产生$Δ_{21}^2 < (7388~\textrm{mK})^2$的上限。这是迄今为止这些红移的最深上限。
英文摘要：
The 21-cm absorption feature reported by the EDGES collaboration is several times stronger than that predicted by traditional astrophysical models. If genuine, a deeper absorption may lead to stronger fluctuations on the 21-cm signal on degree scales (up to 1~Kelvin in rms), allowing these fluctuations to be detectable in nearly 50~times shorter integration times compared to previous predictions. We commenced the "AARTFAAC Cosmic Explorer" (ACE) program, that employs the AARTFAAC wide-field imager, to measure or set limits on the power spectrum of the 21-cm fluctuations in the redshift range $z = 17.9-18.6$ ($Δν= 72.36-75.09$~MHz) corresponding to the deep part of the EDGES absorption feature. Here, we present first results from two LST bins: 23.5-23.75h and 23.5-23.75h, each with 2~h of data, recorded in `semi drift-scan' mode. We demonstrate the application of the new ACE data-processing pipeline (adapted from the LOFAR-EoR pipeline) on the AARTFAAC data. We observe that noise estimates from the channel and time-differenced Stokes~$V$ visibilities agree with each other. After 2~h of integration and subtraction of bright foregrounds, we obtain $2σ$ upper limits on the 21-cm power spectrum of $Δ_{21}^2 < (8139~\textrm{mK})^2$ and $Δ_{21}^2 < (8549~\textrm{mK})^2$ at $k = 0.144~h\,\textrm{cMpc}^{-1}$ for the two LST bins. Incoherently averaging the noise bias-corrected power spectra for the two LST bins yields an upper limit of $Δ_{21}^2 < (7388~\textrm{mK})^2$ at $k = 0.144~h\,\textrm{cMpc}^{-1}$. These are the deepest upper limits thus far at these redshifts.
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