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Dense cloud cores revealed by CO in the low metallicity dwarf galaxy WLM

机译：低金属矮矮星系WLM中CO揭示的致密云芯

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摘要

Understanding stellar birth requires observations of the clouds in which they form. These clouds are dense and self-gravitating, and in all existing observations they are molecular, with H-2 the dominant species and carbon monoxide (CO) the best available tracer(1,2). When the abundances of carbon and oxygen are low compared with that of hydrogen, and the opacity from dust is also low, as in primeval galaxies and local dwarf irregular galaxies(3), CO forms slowly and is easily destroyed, so it is difficult for it to accumulate inside dense clouds(4). Here we report interferometric observations of CO clouds in the local group dwarf irregular galaxy Wolf-Lundmark-Melotte (WLM)(5), which has a metallicity that is 13 per cent of the solar value(6,7) and 50 per cent lower than the previous CO detection threshold. The clouds are tiny compared to the surrounding atomic and H-2 envelopes, but they have typical densities and column densities for CO clouds in the Milky Way. The normal CO density explains why star clusters forming in dwarf irregulars have similar densities to star clusters in giant spiral galaxies. The low cloud masses suggest that these clusters will also be low mass, unless some galaxy-scale compression occurs, such as an impact from a cosmic cloud or other galaxy. If the massive metal-poor globular clusters in the halo of the Milky Way formed in dwarf galaxies, as is commonly believed, then they were probably triggered by such an impact.
机译：了解恒星的诞生需要观察它们形成的云层。这些云是密集的并且是自引力的，在所有现有观测中它们都是分子，H-2是主要物质，一氧化碳（CO）是最好的示踪剂（1,2）。当碳和氧的丰度比氢的丰度低，并且对灰尘的不透明性也很低时，例如在原始星系和局部矮不规则星系中（3），CO形成缓慢且容易被破坏，因此很难它聚集在密云中（4）。在这里，我们报告了在局部群矮不规则星系Wolf-Lundmark-Melotte（WLM）（5）中对CO云进行干涉测量的观测结果，该金属的金属度为太阳值的13％（6,7），低了50％比之前的CO检测阈值高。与周围的原子和H-2包层相比，云很小，但是在银河系中，它们具有典型的CO云密度和柱密度。正常的CO密度解释了为什么在不规则矮星中形成的星团具有与巨型旋涡星系中的星团相似的密度。低云量表明这些星团也将是低质量，除非发生某些星系规模的压缩，例如来自宇宙云或其他星系的撞击。如果人们普遍认为，如果银河系晕圈中大量的贫金属球状星团在矮星系中形成，那么它们很可能是由这种撞击触发的。

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  • 来源
    《Nature》 |2015年第7568期|218-221|共4页
  • 作者

    Rubio Monica; Elmegreen Bruce G.; Hunter Deidre A.; Brinks Elias; Cortes Juan R.; Cigan Phil;

  • 作者单位

    Univ Chile, Dept Astron, Santiago 8320000, Chile;

    IBM Corp, Div Res, TJ Watson Res Ctr, Yorktown Hts, NY 10598 USA;

    Lowell Observ, Flagstaff, AZ 86001 USA;

    Univ Hertfordshire, Ctr Astrophys Res, Hatfield AL10 9AB, Herts, England;

    Joint ALMA Observ, Santiago 7630355, Chile|Natl Radio Astron Observ, Santiago 7630197, Chile;

    New Mexico Inst Min & Technol, Socorro, NM 87801 USA;

  • 收录信息 美国《科学引文索引》(SCI);美国《工程索引》(EI);美国《生物学医学文摘》(MEDLINE);美国《化学文摘》(CA);
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  • 正文语种 eng
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