Planck early results. XVII.Origin of the submillimetre excess dust emission in the Magellanic Clouds
Planck early results. XVII.Origin of the submillimetre excess dust emission in the Magellanic Clouds
复制标题
普朗克的早期成果。
DOI：
10.1051/0004-6361/201116473
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发表时间：
2011
影响因子：
6.5
通讯作者：
et al
中科院分区：
文献类型：
--
作者：
Planck Collaboration ; Ade;P.A.R.;et al
综合光谱能量分布（SED）的大麦哲伦云（LMC）和小麦哲伦云（SMC）出现显着平坦比预期的尘埃模型的基础上，他们的远红外和无线电发射。在这里，我们用普朗克的数据来研究这个毫米过剩的仍然无法解释的起源。在减去前景（银河系）和背景（CMB波动）发射之前，这两个星系的综合SED与以前的测定结果吻合得很好，证实了毫米过剩的存在。在这个初步分析的背景下，我们不提出一个完整的多分量拟合的数据，而是减去无关的星系和尘埃排放的贡献。背景CMB的贡献减去使用内部线性组合（ILC）的方法进行本地周围的星系。从银河系的前景发射被减去作为银河系Hi模板，并在两个星系周围的区域中导出尘埃发射率，并由银河系发射占主导地位。相减后，两个星系的剩余发射与大麦哲伦星云和小麦哲伦星云的原子和分子气体发射密切相关。在LMC毫米过剩可以解释为CMB波动，但一个显着的过剩仍然存在于SMC SED。利用Planck和IRAS-IRIS的100μm数据，合成了这两个星系的热尘埃温度和光学深度图。LMC的温度图显示了一个温暖的内臂的存在，这是斯皮策数据已经发现的，但它也显示了一个以前未被发现的冷外臂的存在。沿着这个臂发现了几个冷区域，其中一些与已知的分子云有关。利用沙尘光学厚度图来约束沙尘热发射率的幂律指数（β）。在500μm以下，LMC和SMC的平均光谱指数分别为β= 1.5和β= 1.2，比银河系中观测到的值明显平坦。此外，在SMC中有证据表明SED在亚毫米级进一步变平，这与SED保持β= 1.5一致的LMC不同。SMC中毫米级粉尘的空间分布遵循气体和热粉尘的分布规律。不同的模型进行了探索，以适应在SMC粉尘排放。它的结论是，毫米的过剩是不太可能造成的非常冷的尘埃排放，它可能是由于旋转的尘埃排放和热尘埃排放的组合，更多的无定形尘埃颗粒比那些存在于我们的银河系。
The integrated spectral energy distributions (SED) of the Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC) appear significantly flatter than expected from dust models based on their far-infrared and radio emission. The still unexplained origin of this millimetre excess is investigated here using thePlanckdata. The integrated SED of the two galaxies before subtraction of the foreground (Milky Way) and background (CMB fluctuations) emission are in good agreement with previous determinations, confirming the presence of the millimetre excess. In the context of this preliminary analysis we do not propose a full multi-component fitting of the data, but instead subtract contributions unrelated to the galaxies and to dust emission. The background CMB contribution is subtracted using an internal linear combination (ILC) method performed locally around the galaxies. The foreground emission from the Milky Way is subtracted as a Galactic Hi template, and the dust emissivity is derived in a region surrounding the two galaxies and dominated by Milky Way emission. After subtraction, the remaining emission of both galaxies correlates closely with the atomic and molecular gas emission of the LMC and SMC. The millimetre excess in the LMC can be explained by CMB fluctuations, but a significant excess is still present in the SMC SED. ThePlanckand IRAS–IRIS data at 100μm are combined to produce thermal dust temperature and optical depth maps of the two galaxies. The LMC temperature map shows the presence of a warm inner arm already found with theSpitzerdata, but which also shows the existence of a previously unidentified cold outer arm. Several cold regions are found along this arm, some of which are associated with known molecular clouds. The dust optical depth maps are used to constrain the thermal dust emissivity power-law index (β). The average spectral index is found to be consistent withβ= 1.5 andβ= 1.2 below 500μm for the LMC and SMC respectively, significantly flatter than the values observed in the Milky Way. Also, there is evidence in the SMC of a further flattening of the SED in the sub-mm, unlike for the LMC where the SED remains consistent withβ= 1.5. The spatial distribution of the millimetre dustexcess in the SMC follows the gas and thermal dust distribution. Different models are explored in order to fit the dust emission in the SMC. It is concluded that the millimetre excess is unlikely to be caused by very cold dust emission and that it could be due to a combination of spinning dust emission and thermal dust emission by more amorphous dust grains than those present in our Galaxy.