Effects of CO-dark Gas on Measurements of Molecular Cloud Stability and the Size–Linewidth Relationship
Effects of CO-dark Gas on Measurements of Molecular Cloud Stability and the Size–Linewidth Relationship
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DOI：
10.3847/1538-4357/ac745f
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发表时间：
2022-05
期刊：
影响因子：
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通讯作者：
T. O’Neill;R. Indebetouw;A. Bolatto;S. Madden;T. Wong
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作者：
T. O’Neill;R. Indebetouw;A. Bolatto;S. Madden;T. Wong
恒星在分子云中形成，因此描述分子云的物理状态对于理解恒星形成过程至关重要。云的结构和稳定性经常使用包括位力参数以及云半径、速度弥散和表面密度之间的拉尔森标度关系等指标来评估。在低金属丰度环境中已经观测到这些量之间偏离典型的银河系关系。在这种条件下，预计在没有相应一氧化碳发射的云包层中氢气的量会很高；因此，这种一氧化碳暗气体可能是所观测到的云特性变化的原因。我们推导出了一些简单的修正方法，这些方法可应用于经验性的团块特性（质量、半径、速度弥散、表面密度和位力参数），以考虑遵循幂律和普卢默质量密度分布的团块中的一氧化碳暗气体。我们发现一氧化碳暗气体不太可能是低金属丰度区域中偏离拉尔森关系的原因，但位力参数可能被系统性地高估了。我们证明，对一氧化碳暗气体进行修正对于准确比较不同环境中分子云的动力学状态和演化至关重要。
Stars form within molecular clouds, so characterizing the physical states of molecular clouds is key to understanding the process of star formation. Cloud structure and stability are frequently assessed using metrics including the virial parameter and Larson scaling relationships between cloud radius, velocity dispersion, and surface density. Departures from the typical Galactic relationships between these quantities have been observed in low-metallicity environments. The amount of H2 gas in cloud envelopes without corresponding CO emission is expected to be high under these conditions; therefore, this CO-dark gas could plausibly be responsible for the observed variations in cloud properties. We derive simple corrections that can be applied to empirical clump properties (mass, radius, velocity dispersion, surface density, and virial parameter) to account for CO-dark gas in clumps following power-law and Plummer mass density profiles. We find that CO-dark gas is not likely to be the cause of departures from Larson’s relationships in low-metallicity regions, but that virial parameters may be systematically overestimated. We demonstrate that correcting for CO-dark gas is critical for accurately comparing the dynamical state and evolution of molecular clouds across diverse environments.