直接观测致密核中向相干态的急剧转变
Direct observation of a sharp transition to coherence in Dense Cores
摘要：
我们目前的NH3观测英仙座B5区域获得的绿岸望远镜（GBT）。这张地图覆盖了一个足够大的区域（~11'x14'），它包含了在以前的尘埃连续体调查中观察到的整个致密核心。NH3（1，1）追踪的致密气体覆盖的区域比测辐射热计观测中发现的尘埃连续特征大得多。核心中心区域的速度频散较小，呈现出与尺度无关的亚音速非热运动。然而，正是由于观测的覆盖范围和高灵敏度，我们才首次探测到相干核心与其周围致密但更湍流的气体之间的跃迁。这种跃迁是尖锐的，在不到0.04 pc的范围内将速度色散增加了2倍（英仙座距离处的31”光束尺寸，约为250 pc）。在转换速度分散的变化是~3公里/秒/秒差距。转捩的存在提供了致密核心的自然定义：具有近似恒定的亚音速非热速度色散的区域。从这里提出的分析，我们不能确认，也不能排除相应的急剧密度过渡。
英文摘要：
We present NH3 observations of the B5 region in Perseus obtained with the Green Bank Telescope (GBT). The map covers a region large enough (~11'x14') that it contains the entire dense core observed in previous dust continuum surveys. The dense gas traced by NH3(1,1) covers a much larger area than the dust continuum features found in bolometer observations. The velocity dispersion in the central region of the core is small, presenting subsonic non-thermal motions which are independent of scale. However, it is thanks to the coverage and high sensitivity of the observations that we present the detection, for the first time, of the transition between the coherent core and the dense but more turbulent gas surrounding it. This transition is sharp, increasing the velocity dispersion by a factor of 2 in less than 0.04 pc (the 31" beam size at the distance of Perseus, ~250 pc). The change in velocity dispersion at the transition is ~3 km/s/pc. The existence of the transition provides a natural definition of dense core: the region with nearly-constant subsonic non-thermal velocity dispersion. From the analysis presented here we can not confirm nor rule out a corresponding sharp density transition.
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