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arXiv 0907.5186astro-ph.GAastro-ph.CO
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远紫外辐射对大麦云云30度区分子云性质的影响

The Influence of Far-Ultraviolet Radiation on the Properties of Molecular Clouds in the 30 Dor Region of the Large Magellanic Cloud

Jorge L. Pineda, Juergen Ott, Ulrich Klein, Tony Wong, Erik Muller, Annie Hughes

摘要:

我们提出了一个完整的12 CO J = 1-0的大麦云(LMC)的突出分子脊的地图获得的22米ATNF Mopra望远镜。该区域从剑鱼座30向南延伸约2度(或1.7kpc),这是本星系群中最活跃的恒星形成区域。这个分子脊的位置是独一无二的,因为它使我们能够研究分子气体的性质作为一个功能的环境辐射场在低金属环境。我们发现分子脊内的CO发射团的物理性质不随远紫外辐射场的强度而变化。由于团簇的峰值CO亮度与辐射场强度无关,因此沿脊的CO-H_2转换因子的观测值似乎需要分子气体的动力学温度升高,而CO发射的角填充因子的降低抵消了这一点。我们发现分子脊和外银河系中CO到H_2的转换因子之间的差异比以前的CO发射研究所报道的要小:将相同的云识别和分析方法应用于我们对LMC分子脊的CO观测和Dame等人(2001)的外星系巡天的CO数据,我们发现,分子脊中CO到H_2的平均转换因子为X_CO =(3.9+/-2.5 10 ^20 cm^-2(K km s^-1)^-1,大约是我们测定的银河系外层云的值的两倍。分子脊中的CO团块的质谱和性质之间的标度关系与银河系分子云的质谱和性质之间的标度关系相似,但不完全相同。

英文摘要:

We present a complete 12CO J = 1-0 map of the prominent molecular ridge in the Large Magellanic Cloud (LMC) obtained with the 22-m ATNF Mopra Telescope. The region stretches southward by ~2 degrees, (or 1.7kpc) from 30 Doradus, the most vigorous star-forming region in the Local Group. The location of this molecular ridge is unique insofar as it allows us to study the properties of molecular gas as a function of the ambient radiation field in a low-metallicity environment. We find that the physical properties of CO-emitting clumps within the molecular ridge do not vary with the strength of the far-ultraviolet (FUV) radiation field. Since the peak CO brightness of the clumps shows no correlation with the radiation field strength, the observed constant value for CO-to-H_2 conversion factor along the ridge seems to require an increase in the kinetic temperature of the molecular gas that is offset by a decrease in the angular filling factor of the CO emission. We find that the difference between the CO-to-H_2 conversion factor in the molecular ridge and the outer Milky Way is smaller than has been reported by previous studies of the CO emission: applying the same cloud identification and analysis methods to our CO observations of the LMC molecular ridge and CO data from the outer Galaxy survey by Dame et al. (2001), we find that the average CO-to-H_2 conversion factor in the molecular ridge is X_CO = (3.9+/-2.5)10^20 cm^-2 (K km s^-1)^-1, approximately twice the value that we determine for the outer Galaxy clouds. The mass spectrum and the scaling relations between the properties of the CO clumps in the molecular ridge are similar, but not identical, to those that have been established for Galactic molecular clouds.

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