Gravity drives the evolution of infrared dark hubs: JVLA observations of SDC13
Gravity drives the evolution of infrared dark hubs: JVLA observations of SDC13
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DOI：
10.1051/0004-6361/201731587
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发表时间：
2018-01
影响因子：
6.5
通讯作者：
G. M. Williams;N. Peretto;A. Avison;A. Duarte-Cabral;G. Fuller
中科院分区：
文献类型：
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作者：
G. M. Williams;N. Peretto;A. Avison;A. Duarte-Cabral;G. Fuller
上下文。星际纤维汇聚的网络，也就是中枢，最近被认为与星系团和大质量恒星的形成有关。了解这些系统的演化与它们内部核心和恒星的形成之间的关系是当前恒星形成研究的核心。目标。目标是研究SDC13原型中心在高角分辨率下的运动学和密度结构，以确定是什么驱动了它的演化和碎裂。方法：研究方法。我们用Jansky甚大阵列和绿岸望远镜在NH_3(1，1)和NH_3(2，2)发射线上绘制了~1000M⊙红外暗中心SDC_(13)。在组合数据集中实现的高角度分辨率使我们能够将探测尺度降至0.07 pC。在对氨气谱线进行拟合后，我们计算了积分强度、质心速度和谱线宽度，以及气体温度和氢气塔密度。结果。所有四个轮毂细丝的单位长度质量在温度上都是超临界的，这与沿途发现的数十个引力束缚核心的存在是一致的。这些地核的规则间隔约为0.37±0.16pC，这表明沿这些超临界细丝运行的引力不稳定性是它们碎裂的原因。观测到的致密气体速度弥散向无星核心的局部增加被认为是这种碎裂过程的结果。利用能量守恒原理，我们估计SDC13岩芯的引力-动能转换效率约为35%。在细丝碎裂的早期阶段，我们看到速度梯度峰值朝向约63%的岩芯，这是预期的。另一个明显的观测特征是在细丝交界处存在最大质量的核心，那里的速度分散最大。我们将其解释为轮毂形态在轮毂中心附近产生最大的加速度梯度的结果。结论。我们提出了一种SDC13中心的演化方案，在该方案中，细丝首先在超音速湍流中形成激波后结构。由于激波中的湍流能量耗散，细丝内的致密气体最初主要是亚音速的。然后，引力接管并开始塑造中枢的演化，既碎裂了细丝，又将气体拉向引力井的中心。通过这样做，引力能在局部(核心)和全局(枢纽中心)势垒极小值中转换为动能。此外，在细丝结合处产生更大的重力加速度梯度，促进了更大质量核心的形成。
Context. Converging networks of interstellar filaments, that is hubs, have been recently linked to the formation of stellar clusters and massive stars. Understanding the relationship between the evolution of these systems and the formation of cores and stars inside them is at the heart of current star formation research. Aims. The goal is to study the kinematic and density structure of the SDC13 prototypical hub at high angular resolution to determine what drives its evolution and fragmentation. Methods. We have mapped SDC13, a ~1000 M⊙ infrared dark hub, in NH3(1,1) and NH3(2,2) emission lines, with both the Jansky Very Large Array and Green Bank Telescope. The high angular resolution achieved in the combined dataset allowed us to probe scales down to 0.07 pc. After fitting the ammonia lines, we computed the integrated intensities, centroid velocities and line widths, along with gas temperatures and H2 column densities. Results. The mass-per-unit-lengths of all four hub filaments are thermally super-critical, consistent with the presence of tens of gravitationally bound cores identified along them. These cores exhibit a regular separation of ~0.37 ± 0.16 pc suggesting gravitational instabilities running along these super-critical filaments are responsible for their fragmentation. The observed local increase of the dense gas velocity dispersion towards starless cores is believed to be a consequence of such fragmentation process. Using energy conservation arguments, we estimate that the gravitational to kinetic energy conversion efficiency in the SDC13 cores is ~35%. We see velocity gradient peaks towards ~63% of cores as expected during the early stages of filament fragmentation. Another clear observational signature is the presence of the most massive cores at the filaments’ junction, where the velocity dispersion is largest. We interpret this as the result of the hub morphology generating the largest acceleration gradients near the hub centre. Conclusions. We propose a scenario for the evolution of the SDC13 hub in which filaments first form as post-shock structures in a supersonic turbulent flow. As a result of the turbulent energy dissipation in the shock, the dense gas within the filaments is initially mostly sub-sonic. Then gravity takes over and starts shaping the evolution of the hub, both fragmenting filaments and pulling the gas towards the centre of the gravitational well. By doing so, gravitational energy is converted into kinetic energy in both local (cores) and global (hub centre) potential well minima. Furthermore, the generation of larger gravitational acceleration gradients at the filament junctions promotes the formation of more massive cores.