PROPERTIES OF DUST GRAINS PROBED WITH EXTINCTION CURVES
PROPERTIES OF DUST GRAINS PROBED WITH EXTINCTION CURVES
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DOI：
10.1088/0004-637x/770/1/27
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发表时间：
2013-01
期刊：
影响因子：
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通讯作者：
T. Nozawa;M. Fukugita
中科院分区：
文献类型：
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作者：
T. Nozawa;M. Fukugita
为了研究银河系(MW)和小麦哲伦星云(SMC)中尘埃颗粒的性质，重新查阅了从紫外线到近红外的消光曲线的现代数据。我们证实了石墨-硅酸盐颗粒混合物产生的消光曲线符合简单的幂函数分布，但在某些最大尺寸处有一个截止点：对于尺寸分布a−Q，参数严格约束为Q=3.5±0.2，对于MW和SMC，最大半径max x=0.2 4±0.0 5μm。颗粒的丰度，因此元素的丰度，受到发红与氢柱密度E(B−V)/NH的限制。如果我们以太阳元素丰度作为兆瓦的标准，>；56%的碳应该在石墨尘中，而根据其可用丰度估计，它在SMC中的<；40%。这一差异和C/Si的相对丰度解释了这两条曲线的不同。我们发现，50%-60%的碳可能不一定在石墨中，而是在无定形或玻璃相中。铁也可能在金属相中，或高达80%的∼在磁铁矿中，而不是在硅酸盐中，因此天文橄榄石中的镁/铁比例是任意的。有了这些替代，晶粒度参数保持不变。尘埃颗粒相对于氢的质量密度是在元素丰度约束下的相对分子质量和相对分子质量。我们强调了近红外消光曲线的波长依赖性在构建尘埃模型中的重要性：如果Aλ∝λ−γ与γ≃1.6，则幂函数粒度模型失败，而当γ≃1.8-2.0时，它是可行的。
Modern data of the extinction curve from the ultraviolet to the near-infrared are revisited to study properties of dust grains in the Milky Way (MW) and the Small Magellanic Cloud (SMC). We confirm that the graphite–silicate mixture of grains yields the observed extinction curve with the simple power-law distribution of the grain size but with a cutoff at some maximal size: the parameters are tightly constrained to be q = 3.5 ± 0.2 for the size distribution a−q and the maximum radius amax = 0.24 ± 0.05 μm, for both MW and SMC. The abundance of grains, and hence the elemental abundance, is constrained from the reddening versus hydrogen column density, E(B − V)/NH. If we take the solar elemental abundance as the standard for the MW, >56% of carbon should be in graphite dust, while it is <40% in the SMC using its available abundance estimate. This disparity and the relative abundance of C to Si explain the difference of the two curves. We find that 50%–60% of carbon may not necessarily be in graphite but in the amorphous or glassy phase. Iron may also be in the metallic phase or up to ∼80% in magnetite rather than in silicates, so that the Mg/Fe ratio in astronomical olivine is arbitrary. With these substitutions, the parameters of the grain size remain unchanged. The mass density of dust grains relative to hydrogen is for the MW and for the SMC under the elemental abundance constraints. We underline the importance of the wavelength dependence of the extinction curve in the near-infrared in constructing the dust model: if Aλ∝λ−γ with γ ≃ 1.6, the power-law grain-size model fails, whereas it works if γ ≃ 1.8–2.0.