Distributed Star Formation throughout the Galactic Center Cloud Sgr B2
Distributed Star Formation throughout the Galactic Center Cloud Sgr B2
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DOI：
10.3847/1538-4357/aaa6d4
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发表时间：
2018-01
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通讯作者：
A. Ginsburg;J. Bally;A. Barnes;N. Bastian;C. Battersby;H. Beuther;C. Brogan;Y. Contreras;J. Corby;J. Darling;C. D. De Pree;R. Galv'an-Madrid;G. Garay;J. Henshaw;T. Hunter;J. Kruijssen;S. Longmore;Xing Lu;F. Meng;Elisabeth A. C. Mills;J. Ott;J. E. Pineda;Á. Sánchez-Monge;P. Schilke;A. Schmiedeke;D. Walker;D. Wilner
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作者：
A. Ginsburg;J. Bally;A. Barnes;N. Bastian;C. Battersby;H. Beuther;C. Brogan;Y. Contreras;J. Corby;J. Darling;C. D. De Pree;R. Galv'an-Madrid;G. Garay;J. Henshaw;T. Hunter;J. Kruijssen;S. Longmore;Xing Lu;F. Meng;Elisabeth A. C. Mills;J. Ott;J. E. Pineda;Á. Sánchez-Monge;P. Schilke;A. Schmiedeke;D. Walker;D. Wilner
我们报道了分辨率≈0的ALMA观测结果。在中央分子带（CMZ）扩展的Sgr B2云的3mm处″5。我们发现了271个致密源，其中大多数小于5000 au。通过排除其他可能性，我们得出结论，这些源由超致密H区和年轻恒星天体（yso）的混合组成。大多数新探测到的源都是带有气体包层的yso，根据它们的光度，它们一定包含恒星质量为M * > 8 M⊙的天体。它们的空间分布分布在约12 × 3 pc的区域，表明Sgr B2正在经历一个扩展的恒星形成事件，而不仅仅是原星团区域内孤立的“星暴”。利用这个新样本，我们研究了Sgr B2中的恒星形成阈值和表面密度关系。虽然所有的YSOs都存在于高柱密度区域（N (h2)≥2 × 10 23 cm−2），但并非所有的高柱密度区域都含有YSOs。观测到的恒星形成的柱密度阈值大大高于太阳附近的云，这意味着要么是高质量恒星形成需要更高的柱密度，要么是CMZ中的任何恒星形成阈值都必须高于附近的云。气体和恒星表面密度之间的关系与局地云的外推是不相容的，相反，Sgr B2中的恒星密度遵循线性Σ * - Σ气体关系，比局地云中观测到的要浅。总之，这些观点表明，需要更高的体积密度阈值来解释CMZ云中的恒星形成。
We report ALMA observations with resolution ≈0.″5 at 3 mm of the extended Sgr B2 cloud in the Central Molecular Zone (CMZ). We detect 271 compact sources, most of which are smaller than 5000 au. By ruling out alternative possibilities, we conclude that these sources consist of a mix of hypercompact H ii regions and young stellar objects (YSOs). Most of the newly detected sources are YSOs with gas envelopes that, based on their luminosities, must contain objects with stellar masses M * ≳ 8 M ⊙ . Their spatial distribution spread over a ∼12 × 3 pc region demonstrates that Sgr B2 is experiencing an extended star formation event, not just an isolated “starburst” within the protocluster regions. Using this new sample, we examine star formation thresholds and surface density relations in Sgr B2. While all of the YSOs reside in regions of high column density ( N ( H 2 ) ≳ 2 × 10 23 cm − 2 ), not all regions of high column density contain YSOs. The observed column density threshold for star formation is substantially higher than that in solar vicinity clouds, implying either that high-mass star formation requires a higher column density or that any star formation threshold in the CMZ must be higher than in nearby clouds. The relation between the surface density of gas and stars is incompatible with extrapolations from local clouds, and instead stellar densities in Sgr B2 follow a linear Σ * – Σ gas relation, shallower than that observed in local clouds. Together, these points suggest that a higher volume density threshold is required to explain star formation in CMZ clouds.