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arXiv 0910.4937astro-ph.GA
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CHAMP + M17 SW中暖气体的观测

CHAMP+ observations of warm gas in M17 SW

J. P. Pérez-Beaupuits, M. Spaans, M. R. Hogerheijde, R. Güsten, A. Baryshev, W. Boland

摘要:

由于气相的主要冷却线是银河系和河外源中星际介质的重要示踪剂,因此,对它们的发射以及发射气体的环境条件的适当和详细的了解,对于观测结果的可靠解释是必要的。利用高分辨率(7”-9”)的中J分子谱线图(~ 3x 3 pc^2),我们的目标是探测M17 SW星云界面区域中温暖(50到几百K)和致密气体(n(H_2)>10^5 cm^-3)的物理条件和空间分布。我们用APEX望远镜上的双色多象元接收机CHAMP+获得了~(12)CO J=6-5和J=7-6跃迁的5 ′.3 × 4 ′.7图,~(13)CO J=6-5谱线,M17 SW中[C I]的{^3P_2}-{^3P_1} 370 μ m精细结构跃迁,采用LTE和non-LTE辐射转移模型约束环境条件。温暖的气体延伸到距离M17西南脊约2.2 pc的地方。~(13)CO J=6-5和[Cl] 370 μ m谱线沿P.A=63 °的带状线具有约1.3pc的较窄的空间范围。[C I] {^3P_2}-{^3P_1} 370 um图的结构和分布表明,它的发射来自密度为10^3 cm^-3量级的团间介质。最热的气体位于云脊附近,靠近电离锋。LTE近似表明嵌入块的激发温度高达~120 K。非LTE模型表明,在密度n(H_2)~5x10^5 cm^-3的团块中,四个选定位置的动力学温度不可能超过230 K,而由J 12 CO中线追踪到的温暖的T_k>100 K且致密的(n(H_2)>10^4 cm^-3)气体仅占分子气体总量的2%左右。在这些位置,团块体积填充因子的范围在0.04和0.11之间。

英文摘要:

Since the main cooling lines of the gas phase are important tracers of the interstellar medium in Galactic and extragalactic sources, proper and detailed understanding of their emission, and the ambient conditions of the emitting gas, is necessary for a robust interpretation of the observations. With high resolution (7"-9") maps (~3x3 pc^2) of mid-J molecular lines we aim to probe the physical conditions and spatial distribution of the warm (50 to few hundred K) and dense gas (n(H_2)>10^5 cm^-3) across the interface region of M17 SW nebula. We have used the dual color multiple pixel receiver CHAMP+ on APEX telescope to obtain a 5'.3x4'.7 map of the J=6-5 and J=7-6 transitions of 12CO, the 13CO J=6-5 line, and the {^3P_2}-{^3P_1} 370 um fine-structure transition of [C I] in M17 SW. LTE and non-LTE radiative transfer models are used to constrain the ambient conditions. The warm gas extends up to a distance of ~2.2 pc from the M17 SW ridge. The 13CO J=6-5 and [C I] 370 um lines have a narrower spatial extent of about 1.3 pc along a strip line at P.A=63 deg. The structure and distribution of the [C I] {^3P_2}-{^3P_1} 370 um map indicate that its emission arises from the interclump medium with densities of the order of 10^3 cm^-3. The warmest gas is located along the ridge of the cloud, close to the ionization front. An LTE approximation indicates that the excitation temperature of the embedded clumps goes up to ~120 K. The non-LTE model suggests that the kinetic temperature at four selected positions cannot exceed 230 K in clumps of density n(H_2)~5x10^5 cm^-3, and that the warm T_k>100 K and dense (n(H_2)>10^4 cm^-3) gas traced by the mid-J 12CO lines represent just about 2% of the bulk of the molecular gas. The clump volume filling factor ranges between 0.04 and 0.11 at these positions.

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