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λ21-cm Interstellar HI Profiles, Critical Ionization Velocities, and Derived Electron Densities
IEEE Transactions on Plasma Science ( IF 1.5 ) Pub Date : 2021-04-14 , DOI: 10.1109/tps.2021.3070237
Gerrit L. Verschuur , Joan T. Schmelz , Mahboubeh Asgari-Targhi

Analysis of neutral hydrogen $\lambda 21$ -cm profiles at high northern and southern Galactic latitudes reveals unexpected properties, connects unanticipated associations, and confirms the fundamental parameters of the interstellar medium. Gaussian decomposition of profiles from the second data release of the Galactic Arecibo $L$ -Band Feed Array (GALFA) confirms earlier results of a pervasive component with a linewidth of order 34 km s −1 , consistent with the critical ionization velocity (CIV) of helium. The ratio of the column density of this component to the entire profile is proportional to the interstellar helium abundance. The results are comparable to the accepted value of the cosmic abundance, 0.085, in the southern Galactic hemisphere, but different for directions in the northern Galactic hemisphere. Normalizing to the cosmic abundance allows us to estimate how much HI is “missing” from the $\lambda 21$ -cm observations in the northern sky, confirming an asymmetry that has been known for decades. These CIV results also predict the volume density of interstellar electrons along different lines of site, which match values derived from pulsar dispersion measures and $\text{H}\alpha $ observations. These results provide strong support for the hypothesis that interstellar $\lambda 21$ -cm HI profile linewidths are modulated by the CIV plasma phenomenon.

中文翻译:

λ21-cm星际HI剖面,临界电离速度和导出的电子密度

中性氢的分析 $ \ lambda 21 $ 北银河和南银河高纬度的cm剖面显示出意料之外的性质,连接了意料之外的关联,并确认了星际介质的基本参数。来自银河Arecibo的第二次数据发布的轮廓的高斯分解 $ L $ -带进料阵列(GALFA)证实了线宽为34 km s -1的弥散成分的早期结果,该线宽 与氦的临界电离速度(CIV)一致。该组分的柱密度与整个剖面的比值与星际氦的丰度成正比。结果与南部银河半球的宇宙丰度的可接受值0.085相当,但对于北部银河半球的方向则有所不同。对宇宙丰度进行归一化可以让我们估算出HI中“缺失”了多少HI。 $ \ lambda 21 $ -cm观测到的北部天空,证实了几十年来已知的不对称性。这些CIV结果还预测了沿不同站点线的星际电子的体积密度,该密度与从脉冲星色散测度和 $ \ text {H} \ alpha $ 观察。这些结果为星际假说提供了有力的支持。 $ \ lambda 21 $ -cm HI轮廓线宽由CIV等离子体现象调制。
更新日期:2021-05-11
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