龙之母：龙云（红外暗云 G028.37+00.07）中一个巨大的宁静核心
Mother of Dragons: A Massive, quiescent core in the dragon cloud (IRDC G028.37+00.07)
AI总结：
本文利用 ALMA 高角分辨率观测分析龙云中的大质量核心 C2c1，发现其碎裂为两个致密核心且维里参数小于1，为存在大质量前恒星核心提供了证据。
摘要：
背景：大质量恒星形成的核心吸积模型要求分子云中存在大质量、无恒星的核心。然而，目前已知的此类真正大质量、单体核心的候选体数量很少。目的：本文分析了一个位于被广泛研究的红外暗云（IRDC）——“龙云”（也称为 G028.37+00.07 或“Cloud C”）中的大质量核心。该核心（C2c1）位于 IRDC 中心附近一条大致等间距的活跃恒星形成核心链的末端。方法：我们展示了该大质量核心新的高角分辨率 1 mm ALMA 尘埃连续谱和分子谱线观测。结果：高角分辨率观测显示该区域碎裂为两个核心 C2c1a 和 C2c1b，它们分别保留了显著的本底扣除后质量 23 Msun 和 2 Msun（未扣除本底时为 31 Msun 和 6 Msun）。在我们最高角分辨率图像（0.200 角秒，0.005 pc ~ 1000 AU）的尺度上，这些核心似乎没有进一步碎裂。我们发现这些核心非常致密（nH2 > 10^6 cm-3），并且只有跨声速的非热运动（Ms ~ 1）。质量、密度和内部运动共同表明维里参数 < 1，这暗示核心处于引力不稳定状态，除非受到强度约 1 - 10 mG 的强磁场支撑。通过 CO 谱线观测，我们发现有初步证据表明朝向质量较小的核心存在微弱的分子外流，而质量较大的核心仍然没有任何恒星形成指示。结论：我们提供了存在一个大质量、前恒星核心的证据，这对大质量恒星形成理论具有重要意义。该源值得后续更高角分辨率观测，以进一步评估其单体和前恒星性质。
英文摘要：
Context: Core accretion models of massive star formation require the existence of massive, starless cores within molecular clouds. Yet, only a small number of candidates for such truly massive, monolithic cores are currently known. Aims: Here we analyse a massive core in the well-studied infrared-dark cloud (IRDC) called the 'dragon cloud' (also known as G028.37+00.07 or 'Cloud C'). This core (C2c1) sits at the end of a chain of a roughly equally spaced actively star-forming cores near the centre of the IRDC. Methods: We present new high-angular resolution 1 mm ALMA dust continuum and molecular line observations of the massive core. Results: The high-angular resolution observations show that this region fragments into two cores C2c1a and C2c1b, which retain significant background-subtracted masses of 23 Msun and 2 Msun (31 Msun and 6 Msun without background subtraction), respectively. The cores do not appear to fragment further on the scales of our highest angular resolution images (0.200 arcsec, 0.005 pc ~ 1000 AU). We find that these cores are very dense (nH2 > 10^6 cm-3) and have only trans-sonic non-thermal motions (Ms ~ 1). Together the mass, density and internal motions imply a virial parameter of < 1, which suggests the cores are gravitationally unstable, unless supported by strong magnetic fields with strengths of ~ 1 - 10 mG. From CO line observations, we find that there is tentative evidence for a weak molecular outflow towards the lower-mass core, and yet the more massive core remains devoid of any star formation indicators. Conclusions: We present evidence for the existence of a massive, pre-stellar core, which has implications for theories of massive star formation. This source warrants follow-up higher-angular-resolution observations to further assess its monolithic and pre-stellar nature.
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