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arXiv 1104.3899astro-ph.GA
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大质量恒星形成团的物理性质:分子示踪剂的系统比较

The Physical Properties of High-Mass Star-Forming Clumps: A Systematic Comparison of Molecular Tracers

Megan Reiter, Yancy Shirley, Jingwen Wu, Crystal Brogan, Alwyn Wootten, Ken'ichi Tatematsu

摘要:

我们对27个与水脉泽发射相一致的高质量团簇样品进行了HCO+和H^13CO+、N2 H+、HCS+、HCN和HN^13C、SO和^34SO、CCH、SO_2和CH_3OH-E的观测。所有转换都以几乎相同的分辨率(30”)观察或卷积,从而允许对从映射转换导出的块属性进行相互比较。我们发现N2 H+的排放是空间分化的灰尘和其他分子相比,对一些非常明亮的核心(10 27)和N2 H+的积分强度不相关以及灰尘连续通量。我们计算有效激发密度,n_eff,所需的密度激发1 K线在T_kin=20 K气体的每个分子示踪剂。具有较大有效激发密度(n_eff > 10^5 cm^-3)的分子示踪剂的强度似乎与亚毫米尘埃连续谱强度的相关性更强。团块的中值大小与示踪剂的n_eff(其跨越超过三个数量级)反相关。维里质量与n_eff不相关,特别是在线光学厚的情况下,因为线宽可以通过非维里运动显著加宽。团块的中值质量表面密度和中值体积密度与n_eff相关,这表明在导出核的集合的平均性质时理解分子示踪剂的激发条件的重要性。

英文摘要:

We present observations of HCO+ and H^13CO+, N2H+, HCS+, HCN and HN^13C, SO and ^34SO, CCH, SO_2, and CH_3OH-E towards a sample of 27 high-mass clumps coincident with water maser emission. All transitions are observed with or convolved to nearly identical resolution (30"), allowing for inter-comparison of the clump properties derived from the mapped transitions. We find N2H+ emission is spatially differentiated compared to the dust and the other molecules towards a few very luminous cores (10 of 27) and the N2H+ integrated intensity does not correlate well with dust continuum flux. We calculate the effective excitation density, n_eff, the density required to excite a 1 K line in T_kin=20 K gas for each molecular tracer. The intensity of molecular tracers with larger effective excitation densities (n_eff > 10^5 cm^-3) appear to correlate more strongly with the submillimeter dust continuum intensity. The median sizes of the clumps are anti-correlated with the n_eff of the tracers (which span more than three orders of magnitude). Virial mass is not correlated with n_eff, especially where the lines are optically thick as the linewidths may be broadened significantly by non-virial motions. The median mass surface density and median volume density of the clumps is correlated with n_eff indicating the importance of understanding the excitation conditions of the molecular tracer when deriving the average properties of an ensemble of cores.

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