arXiv 1203.20122012-03-09astro-ph.GA

来自NGC 2024的[12 CII]和[13 CII] 158 μ m发射：离子化碳的大柱密度

[12CII] and [13CII] 158 mum emission from NGC 2024: Large column densities of ionized carbon

U. U. Graf, R. Simon, J. Stutzki, S. W. J. Colgan, X. Guan, R. Güsten, R. Hartogh, C. E. Honingh, H. -W. Hübers

DOI：: 10.1051/0004-6361/201218930

摘要：

背景：我们使用[12 CII]和[13 CII]观测分析了NGC 2024 HII区域和分子云界面。目的：我们试图深入了解分子云和HII区之间的界面层的物理结构。方法.在158 μm处观测到的高空间和光谱分辨率的[12 CII]和[13 CII]发射使我们能够研究电离锋的详细结构，并估计PDR中电离碳层的柱密度和温度。结果：[12 CII]发射密切遵循8妈妈的连续分布。在大部分的源，谱线有两个速度峰值类似于罕见的CO同位素线。[13 CII]发射在边缘电离前沿附近被检测到。它只有一个单一的速度分量，这意味着[12 CII]线的形状是由自吸收引起的。在[13 CII]中观察到的异常超精细线强度比尚不能解释。结论：我们对这两种同位素的分析结果表明，在发射[CII]线的气体中，总柱密度为N（H）~1.6 \times 10^23 cm^-2。这种气体的大部分必须处于几百K的温度下。自吸收是由温度较低（T<=100 K）的前景成分引起的，其柱密度为N（H）~10^22 cm^-2。

英文摘要：

Context: We analyze the NGC 2024 HII region and molecular cloud interface using [12CII] and [13CII] observations. Aims: We attempt to gain insight into the physical structure of the interface layer between the molecular cloud and the HII region. Methods. Observations of [12CII] and [13CII] emission at 158 μm with high spatial and spectral resolution allow us to study the detailed structure of the ionization front and estimate the column densities and temperatures of the ionized carbon layer in the PDR. Results: The [12CII] emission closely follows the distribution of the 8 mum continuum. Across most of the source, the spectral lines have two velocity peaks similar to lines of rare CO isotopes. The [13CII] emission is detected near the edge-on ionization front. It has only a single velocity component, which implies that the [12CII] line shape is caused by self-absorption. An anomalous hyperfine line-intensity ratio observed in [13CII] cannot yet be explained. Conclusions: Our analysis of the two isotopes results in a total column density of N(H)~1.6\times10^23 cm^-2 in the gas emitting the [CII] line. A large fraction of this gas has to be at a temperature of several hundred K. The self-absorption is caused by a cooler (T<=100 K) foreground component containing a column density of N(H)~10^22 cm^-2.

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