Herschel/HIFI observations of interstellar OH+ and H2O+ towards W49N: a probe of diffuse clouds with a small molecular fraction
Herschel/HIFI observations of interstellar OH+ and H2O+ towards W49N: a probe of diffuse clouds with a small molecular fraction
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DOI：
10.1051/0004-6361/201015077
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发表时间：
2010-10-01
影响因子：
6.5
通讯作者：
Zmuidzinas, J.
中科院分区：
文献类型：
--
作者：
Neufeld, D. A.;Goicoechea, J. R.;Zmuidzinas, J.
我们报告的吸收星际羟基阳离子和水的阳离子，沿着视线明亮的连续光源W 49 N的检测。我们用Herschel的HIFI仪器，在双光束开关模式下，观测了972 GHz的OH ~+的N = 1-0跃迁和1115 GHz的ortho-H_2 O ~+的1（11）-0（00）跃迁。由此产生的光谱显示邻-H2O+的吸收，和强烈的吸收OH+，在前景材料的速度在0至70公里秒（-1）相对于当地标准的休息。推断的OH+/H2O+丰度比范围从接近3到接近15，这意味着观测到的OH+出现在小分子分数的云中，在2-8%的范围内。OH+和H2O+在多普勒速度空间中的分布证实了这一结论，这与通过21 cm吸收测量观察到的原子氢的分布相似，而与其他分子示踪剂的典型分布不同。观测到的OH+/H丰度比只有几个x10（-8），这表明氢原子的宇宙射线电离率为0.6-2.4 x10（-16）s（-1），这与之前通过对星际H-3（+）和其他物质的观测推断出的银河系盘中弥漫云的估计非常一致。
We report the detection of absorption by interstellar hydroxyl cations and water cations, along the sight-line to the bright continuum source W49N. We have used Herschel's HIFI instrument, in dual beam switch mode, to observe the 972 GHz N = 1-0 transition of OH+ and the 1115 GHz 1(11)-0(00) transition of ortho-H2O+. The resultant spectra show absorption by ortho-H2O+, and strong absorption by OH+, in foreground material at velocities in the range 0 to 70 km s(-1) with respect to the local standard of rest. The inferred OH+/H2O+ abundance ratio ranges from similar to 3 to similar to 15, implying that the observed OH+ arises in clouds of small molecular fraction, in the 2-8% range. This conclusion is confirmed by the distribution of OH+ and H2O+ in Doppler velocity space, which is similar to that of atomic hydrogen, as observed by means of 21 cm absorption measurements, and dissimilar from that typical of other molecular tracers. The observed OH+/H abundance ratio of a few x10(-8) suggests a cosmic ray ionization rate for atomic hydrogen of 0.6-2.4 x 10(-16) s(-1), in good agreement with estimates inferred previously for diffuse clouds in the Galactic disk from observations of interstellar H-3(+) and other species.