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首页> 外文期刊>The Astrophysical journal >GALACTIC CENTER EXTINCTION: EVIDENCE OF METALLIC NEEDLES IN THE GENERAL INTERSTELLAR MEDIUM
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GALACTIC CENTER EXTINCTION: EVIDENCE OF METALLIC NEEDLES IN THE GENERAL INTERSTELLAR MEDIUM

机译：银河系中心灭绝：普通星际介质中金属针的证据

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摘要

The extinction curve derived from Infrared Space Observatory mid-infrared observations of the Galactic center (GC) exhibits a surprisingly flat behavior in the ～3-8 μm region, contrary to the deep minimum expected from standard interstellar dust models consisting of bare silicate and graphite dust particles. We show that this extinction is likely caused by the presence of metallic needles in the interstellar medium (ISM) toward the GC. If the needles contribute only to the 3-8 μm extinction, they must have a long-wavelength cutoff at ～8 μm and therefore a typical length over radius ratio of ～600, smaller than the ～3 x 10~3 aspect ratio determined for the needles in Cas A. Homogeneously distributed throughout the ISM, they comprise only a minor mass fraction of the ISM, with a needle-to-H mass ratio of ～5 x 10~(-6), which is equivalent to 0.14% of the silicate dust mass. Their total ISM abundance then can be readily explained by the combined production in supernovae and O-rich stellar outflows. The GC observations show that metallic needles, in spite of their low abundance or nonuniform distribution, can be the dominant source of opacity in the 3-8 μm wavelength region. However, expelled into the intergalactic medium, their abundance is too low to cause any dimming of cosmological sources, and their length is too short to make them a significant source of submilrimeter emission.
机译：来自银河中心（GC）的红外空间天文台中红外观测结果的消光曲线在〜3-8μm区域表现出令人惊讶的平坦行为，这与标准的星际尘埃模型（由裸露的硅酸盐和石墨组成）所预期的最小最小值相反灰尘颗粒。我们表明，这种灭绝很可能是由星际介质（ISM）中朝向GC的金属针的存在引起的。如果针仅对3-8μm消光有贡献，则它们必须在〜8μm处有长波长截止，因此典型的长度与半径之比为〜600，小于确定的〜3 x 10〜3长宽比。均匀分布在整个ISM中，它们仅占ISM的一小部分，针与H的质量比为〜5 x 10〜（-6），相当于质量分数的0.14％硅酸盐粉尘团。然后，它们的总ISM丰度可以通过超新星和富含O的恒星流出的联合生产来容易地解释。 GC的观察表明，尽管金属针的丰度低或分布不均匀，但它们仍可能是3-8μm波长区域中不透明的主要来源。但是，被驱逐到银河系中间介质中时，它们的丰度太低而无法导致宇宙学源变暗，并且它们的长度太短，不足以使其成为亚微米级发射的重要来源。

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