LABOCA observations of giant molecular clouds in the southwest region of the Small Magellanic Cloud
LABOCA observations of giant molecular clouds in the southwest region of the Small Magellanic Cloud
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LABOCA 观测小麦哲伦星云西南地区巨分子云
DOI：
10.1051/0004-6361/200913372
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发表时间：
2010
影响因子：
6.5
通讯作者：
中科院分区：
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背景分子气体的数量是了解星系中未来恒星形成的关键。由于在稠密且寒冷的云层中很难直接观测到 H2，因此使用了 CO 分子等示踪剂。然而，特别是在金属丰度较低的情况下，二氧化碳只能追踪云层的屏蔽内部。在这种情况下，毫米级尘埃排放可以用作示踪剂来揭示总的致密气体质量。然而，之前的研究对小麦哲伦星云 (SMC) 巨分子云样本中的连续 SIMBA 1.2 毫米发射推导出的质量和维里质量（理解为追踪云的全部潜力）进行了比较，发现这两个量之间存在差异，需要解释。目的我们试图更准确地评估在 SMC 巨分子云样本中观察到的尘埃发射中可能存在的不确定性。我们重点对巨分子云中检测到CO的最致密部分进行质量比较，以证实之前观测到的质量差异。方法利用APEX望远镜上的LABOCA相机获得了SMC西南区域的新观测结果。之前在 CO 中观察到的所有巨型分子云均被检测到，并将它们在 870μm 处的发射与辅助数据进行比较。估计对亚毫米发射的不同贡献以及灰尘特性（温度、发射率），以精确确定分子云质量。结果在 SMC 西南地区的巨型分子云中观测到的（亚）毫米发射主要是灰尘发射，并推导出每个云中检测到 CO 的部分的质量，并将其与维里质量进行比较。使用 LABOCA 观测结果证实了两种方法之间的质量差异为 870μm：维里质量平均比从尘埃排放推断出的致密气体质量低 4 倍，这与我们银河系中等效云的观测结果形成鲜明对比。结论目前，SMC 中这种质量差异的根源仍然未知。这种效应的直接解释是用于计算维里质量的 CO 线宽并不能测量气体的完整速度分布。还讨论了灰尘特性的几何效应和不确定性。
ContextThe amount of molecular gas is a key to understanding the future star formation in a galaxy. Because H2is difficult to observe directly in dense and cold clouds, tracers such as the CO molecule are used. However, at low metallicities especially, CO only traces the shielded interiors of the clouds. In this context, millimeter dust emission can be used as a tracer to unveil the total dense gas masses. However, the comparison of masses deduced from the continuum SIMBA 1.2 mm emission and virial masses (understood to trace the entire potential of the clouds) in a sample of giant molecular clouds in the Small Magellanic Cloud (SMC) by previous studies found a discrepancy between these two quantities that requires explanation.AimsWe attempt to more accurately assess possible uncertainties in the dust emission observed in the sample of giant molecular clouds from the SMC. We focus on the mass comparison in the densest parts of the giant molecular clouds where CO is detected to confirm the mass discrepancy previously observed.MethodsNew observations of the southwest region of the SMC were obtained with the LABOCA camera on the APEX telescope. All the giant molecular clouds previously observed in CO are detected and their emission at 870μm is compared to ancillary data. The different contributions to the sub-millimeter emission are estimated, as well as dust properties (temperatures, emissivities), to determine molecular cloud masses precisely.ResultsThe (sub-)millimeter emission observed in the giant molecular clouds in the southwest region of the SMC is dominated by dust emission, and masses are deduced for the part of each cloud where CO is detected and compared to the virial masses. The mass discrepancy between both methods is confirmed at 870μm using the LABOCA observations: the virial masses are on average 4 times lower than the masses of dense gas inferred from dust emission, in contrast to what is observed for equivalent clouds in our Galaxy.ConclusionsAt present, the origin of this mass discrepancy in the SMC remains unknown. The direct interpretation of this effect is that the CO linewidth used to compute virial masses do not measure the full velocity distribution of the gas. Geometrical effects and uncertainties in the dust properties are also discussed.
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DOI：
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发表时间：
2007
期刊：
影响因子：
--
作者：
V. Lebouteiller;J. Bernard;B. Brandl;D. Whelan;Yanling Wu;V. Charmandaris;D. Devost;J. Houck
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影响因子：
6.5
作者：
S. Nikolić;G. Garay;M. Rubio;L. Johansson
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DOI：
10.1086/321715
发表时间：
2001-06
期刊：
The Astrophysical Journal Letters
影响因子：
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作者：
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通讯作者：
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DOI：
--
发表时间：
2003
期刊：
影响因子：
--
作者：
W. Rolleston;K. Venn;E. Tolstoy;P. Dufton
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P. Dufton
毫米尘埃连续发射揭示了小麦哲伦星云中巨分子云的真实质量
DOI：
--
发表时间：
2007
期刊：
影响因子：
--
作者：
C. Bot;C. Bot;F. Boulanger;Mónica Rubio;F. Rantakyrö
通讯作者：
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