I-GALFA Hi 21 cm测线中的Hi壳和Supershell：I.与超新星遗迹有关的快速膨胀Hi壳层
Hi Shells and Supershells in the I-GALFA Hi 21-cm Line Survey: I. Fast-Expanding Hi Shells Associated with Supernova Remnants
摘要：
我们使用来自内星系阿雷西博L波段馈源阵列（I-GALFA）Hi巡天的21厘米线数据，在1 \approx 32 \arcdeg到77 \arcdeg经度范围内搜索与银河系超新星遗迹（SNR）相关的快速膨胀Hi壳层。在该区域已知的39个银河系SNRs中，我们在四个SNRs中发现了这样的Hi壳层：W 44，G54.4-0.3，W51 C和CTB 80。所有这四个都是以前在低分辨率调查中发现的，其中三个（不包括G54.4-0.3）以前用阿雷西博望远镜研究过。然而，一个显着的新的结果是，在非常高的正和负的速度在W 44从后退和接近部分的Hi膨胀壳，分别检测到Hi排放。这是第一次检测到的双方扩大壳与SNR在高21厘米发射。高分辨率I-GALFA测量数据还揭示了一个与G54.4-0.3相关的突出的具有高度圆对称性的膨胀Hi壳。我们探讨了四个信噪比的物理特性，并讨论了什么区别于其他信噪比在调查区域。我们的结论是，这四个SNR很可能是核心坍缩超新星与相对致密（>~1 cm^-3）的环境介质相互作用的残留物，我们还讨论了Hi 21 cm谱线中SNR的可见性。
英文摘要：
We search for fast-expanding Hi shells associated with Galactic supernova remnants (SNRs) in the longitude range l \approx 32\arcdeg to 77\arcdeg using 21-cm line data from the Inner-Galaxy Arecibo L-band Feed Array (I-GALFA) Hi survey. Among the 39 known Galactic SNRs in this region, we find such Hi shells in four SNRs: W44, G54.4-0.3, W51C, and CTB 80. All four were previously identified in low-resolution surveys, and three of those (excluding G54.4-0.3) were previously studied with the Arecibo telescope. A remarkable new result, however, is the detection of Hi emission at both very high positive and negative velocities in W44 from the receding and approaching parts of the Hi expanding shell, respectively. This is the first detection of both sides of an expanding shell associated with an SNR in Hi 21-cm emission. The high-resolution I-GALFA survey data also reveal a prominent expanding Hi shell with high circular symmetry associated with G54.4-0.3. We explore the physical characteristics of four SNRs and discuss what differentiates them from other SNRs in the survey area. We conclude that these four SNRs are likely the remnants of core-collapse supernovae interacting with a relatively dense (>~1 cm^-3) ambient medium, and we discuss the visibility of SNRs in the Hi 21-cm line.
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