HiFAST：一个用于FAST的HI数据校准与成图流水线
HiFAST: an HI data calibration and imaging pipeline for FAST
AI总结：
本文提出了专用于FAST望远镜的模块化HI数据校准与成图流水线HiFAST，其校准精度和测量结果与Arecibo望远镜高度一致，将助力宇宙中性氢研究产生重要科学发现。
摘要：
五百米口径球面射电望远镜（FAST）拥有最大的口径和19波束L波段接收机，使其在研究宇宙中的中性氢原子气体（HI）方面具有强大的能力。我们提出了HiFAST（https://hifast.readthedocs.io），这是一个专用、模块化且自包含的校准与成图流水线，用于处理FAST的HI数据。该流水线包括随频率变化的噪声二极管校准、基线拟合、使用基于FFT方法去除驻波、流量密度校准、杂散辐射校正以及网格化以生成数据立方体。这些模块可以根据需要组合，以处理大多数FAST观测模式的数据：跟踪、漂移扫描、On-The-Fly mapping以及它们的大多数变体。使用HiFAST，来自所有19个波束的已校准光谱的RMS噪声仅比理论预期略高（约5%）。对于扩展源M33和点源的结果与Arecibo的结果一致。M33的矩图（0、1和2）与Arecibo星系环境巡天（AGES）的结果非常吻合，相对差异小于10%。对于来自Arecibo Legacy Fast ALFA（ALFALFA）巡天中信噪比S/N >10的221个共同样本源，两个数据集之间积分流量密度$S_{\mathrm{int}}$相对差异的平均值约为0.005%，离散度为15.4%。对具有七次观测的23个源的积分流量密度的进一步检查表明，具有明亮天体的源（$S_\mathrm{int}$ $ > 2.5$ Jy km s$^{-1}$）的流量密度方差小于5%。我们的测试表明，配备高效、精确且用户友好的HiFAST流水线的FAST望远镜，将在宇宙HI研究中产生大量重要的科学发现。
英文摘要：
The Five-hundred-meter Aperture Spherical radio Telescope (FAST) has the largest aperture and a 19-beam L-band receiver, making it powerful for investigating the neutral hydrogen atomic gas (HI) in the universe. We present HiFAST (https://hifast.readthedocs.io), a dedicated, modular, and self-contained calibration and imaging pipeline for processing the HI data of FAST. The pipeline consists of frequency-dependent noise diode calibration, baseline fitting, standing wave removal using an FFT-based method, flux density calibration, stray radiation correction, and gridding to produce data cubes. These modules can be combined as needed to process the data from most FAST observation modes: tracking, drift scanning, On-The-Fly mapping, and most of their variants. With HiFAST, the RMS noises of the calibrated spectra from all 19 beams were only slightly (~ 5%) higher than the theoretical expectation. The results for the extended source M33 and the point sources are consistent with the results from Arecibo. The moment maps (0,1 and 2) of M33 agree well with the results from the Arecibo Galaxy Environment Survey (AGES) with a fractional difference of less than 10%. For a common sample of 221 sources with signal-to-noise ratio S/N >10 from the Arecibo Legacy Fast ALFA (ALFALFA) survey, the mean value of fractional difference in the integrated flux density, $S_{\mathrm{int}}$, between the two datasets is approximately 0.005 %, with a dispersion of 15.4%. Further checks on the integrated flux density of 23 sources with seven observations indicate that the variance in the flux density of the source with luminous objects ($S_\mathrm{int}$ $ > 2.5$ Jy km s$^{-1}$) is less than 5%. Our tests suggest that the FAST telescope, with the efficient, precise, and user-friendly pipeline HiFAST, will yield numerous significant scientific findings in the investigation of the HI in the universe.
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