Visibility of old supernova remnants in H i 21‐cm emission line
Visibility of old supernova remnants in H i 21‐cm emission line
复制标题
H i 21 厘米发射线中旧超新星遗迹的可见度
DOI：
10.1111/j.1365-2966.2004.07579.x
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发表时间：
2003
期刊：
影响因子：
--
通讯作者：
B. Kang
中科院分区：
文献类型：
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作者：
B. Kang
我们估计了银河系中H i 21-cm发射线中可探测到的老辐射超新星遗迹（SNRs）的数量。我们假设，旧的信噪比包括扩大H i壳，他们是可见的，如果视线速度是足够的银河系背景H i发射的速度范围之外。这一能见度标准使得计算背景污染和与观测结果进行比较成为可能。在我们的模型中，银盘充满了中等密度（约0.1 cm−3）的原子气体，代表温暖的中性星际介质。我们假设，只有Ia型超新星产生孤立的SNR与扩大H i壳，或'H i SNR'。根据我们的研究结果，由于银河系背景H i辐射的污染，可见SNR的数量限制在10270，或总H i SNR的109%。它们沿着切点的轨迹集中。望远镜的灵敏度进一步限制了数量。通过与观测值的比较发现，观测到的H i SNR数（≤25）远小于预期值。一个合理的解释是，以前的观测研究，主要是在无线电连续谱中识别的SNR，错过了大部分的H i SNR，因为它们太微弱了，在无线电连续谱中是可见的。我们提出，在大尺度（l，v）图中，从银河系背景H i发射中突出的微弱的，扩展的H i 21-cm发射线翼可能是H i SNR的可能候选者，尽管我们的初步结果表明，它们的数量比银河系内部预期的要少得多。我们的结论是，一个可能的解释是，在银河系内部的H i SNR的数量少，星际空间有很大程度上充满了一个非常稀薄的气体在三相星际介质（ISM）模型，而不是与温暖的中性介质的中等密度。
We estimate the number of old, radiative supernova remnants (SNRs) detectable in H i 21-cm emission line in the Galaxy. We assume that old SNRs consist of expanding H i shells and that they are visible if the line-of-sight velocities are sufficiently outside the velocity range of the Galactic background H i emission. This criterion of visibility makes it possible to calculate the background contamination and to make a comparison with observation. The Galactic disc in our model is filled with atomic gas of moderate (∼0.1 cm−3) density representing the warm neutral interstellar medium. We assume that only Type Ia supernovae produce isolated SNRs with expanding H i shells, or ‘H i SNRs’. According to our result, the contamination due to the Galactic background H i emission limits the number of visible SNRs to ≃270, or ≃9 per cent of the total H i SNRs. They are concentrated along the loci of tangential points. The telescope sensitivity further limits the number. We compare the result with observations to find that the observed number (≤25) of H i SNRs is much less than expected. A plausible explanation is that previous observational studies, which were made towards the SNRs identified mostly in radio continuum, missed most of the H i SNRs because they are too faint to be visible in radio continuum. We propose that the faint, extended H i 21-cm emission line wings protruding from the Galactic background H i emission in large-scale (l, v) diagrams could be possible candidates for H i SNRs, although our preliminary result shows that their number is considerably less than expected in the inner Galaxy. We conclude that a possible explanation for the small number of H i SNRs in the inner Galaxy is that the interstellar space there is largely filled with a very tenuous gas as in the three-phase interstellar medium (ISM) model, not with the warm neutral medium of moderate density.