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arXiv 0804.0849astro-ph
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在用MERLIN观测的三个河外源方向上50- AU尺度的银河系HI

Galactic HI on the 50-AU scale in the direction of three extra-galactic sources observed with MERLIN

W. M. Goss, A. M. S. Richards, T. W. B. Muxlow, P. Thomasson

摘要:

我们提出银河系21厘米HI吸收的MERLIN观测,角分辨率为c。0.1-0.2角秒,速度分辨率为0.5km/s,观测到3个中低纬(-8< b <-12度)河外射电源3C 111、3C 123和3C 161,它们都是严重红化的。HI吸收观察到对解决的背景排放源高达c。在3C~123和3C~161的1- 1.5arcsec范围内,我们区分了不透明度分布的细节。这项研究是MERLIN对星际HI小尺度结构的第二次调查(早期的工作是在致密源3C 138和3C 147的方向上探测银河HI)。0.1角秒尺度介于用其他固定元件干涉仪进行的HI吸收研究(分辨率为1至10角秒)和VLBI研究(分辨率为10至20毫角秒)之间。在1角秒(约500天文单位)的尺度上,银河系HI不透明度的显著变化超过1-1.5,在3C 161方向上被确定,信噪比至少为10西格玛。在3C 123的方向上,在2.5-3西格玛水平检测到HI不透明度在约1水平的可能波动。

英文摘要:

We present MERLIN observations of Galactic 21-cm HI absorption at an angular resolution of c. 0.1-0.2 arcsec and a velocity resolution of 0.5 km/s, in the direction of three moderately low latitude (-8< b <-12 deg) extragalactic radio sources, 3C111, 3C123 and 3C161, all of which are heavily reddened. HI absorption is observed against resolved background emission sources up to c. 2 arcsec in extent and we distinguish details of the opacity distribution within 1-1.5 arcsec regions towards 3C~123 and 3C~161. This study is the second MERLIN investigation of small scale structure in interstellar HI (earlier work probed Galactic HI in the directions of the compact sources 3C138 and 3C147). The 0.1-arcsec scale is intermediate between HI absorption studies made with other fixed element interferometers with resolution of 1 to 10 arcsec and VLBI studies with resolutions of 10-20 milli-arcsec. At a scale of 1 arcsec (about 500 AU), prominent changes in Galactic HI opacity in excess of 1-1.5 are determined in the direction of 3C161 with a signal-to-noise ratio of at least 10 sigma. Possible fluctuations in the HI opacity at the level of about 1 are detected at the 2.5-3 sigma level in the direction of 3C123.

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