GRAVITATIONAL CONTRACTION VERSUS SUPERNOVA DRIVING AND THE ORIGIN OF THE VELOCITY DISPERSION–SIZE RELATION IN MOLECULAR CLOUDS
GRAVITATIONAL CONTRACTION VERSUS SUPERNOVA DRIVING AND THE ORIGIN OF THE VELOCITY DISPERSION–SIZE RELATION IN MOLECULAR CLOUDS
复制标题
引力收缩与超新星驱动以及分子云中速度色散-尺寸关系的起源
DOI：
--
复制
发表时间：
2015
期刊：
影响因子：
--
通讯作者：
C. Baczynski
中科院分区：
文献类型：
--
作者：
J. C. Ibáñez;M. Mac Low;R. Klessen;C. Baczynski
分子云(MC)观测表明，在表面密度不变的情况下，云具有非热速度弥散，随云大小的变化为σ∝r1/2；对于不同的面密度尺度，随云的大小和表面密度的变化，σ2∝RΣ。推动这些混乱运动的能源仍然知之甚少。我们描述了在磁化、分层、超新星(SN)驱动的星际介质(包括扩散加热和辐射冷却)的数值模拟中观察到的云团中的速度色散，在我们包括气体自引力的影响之前和之后。我们比较了在模拟云团中测量的速度离散度、大小和表面密度之间的关系，以及在银河系MC观测中发现的关系。我们在自重力开始之前的模拟表明，外部SN爆炸本身并不能驱动稠密云中观测到的量级的湍流运动。另一方面，在我们的模型中，当重力约束的云开始崩塌时，自重力会导致非热运动，接近观察到的速度色散、大小和表面密度之间的关系。能量守恒表明，观察到的行为与动能与引力能成正比是一致的。然而，我们的模型中的云在任何时候都没有达到稳定平衡状态的迹象，即使是强磁化的云也是如此。我们的结论是，受引力约束的MC总是处于引力收缩状态，它们的性质是这种混沌崩溃的自然结果。为了与观测到的恒星形成效率一致，这一过程必须通过云的早期破坏来终止，假设是从内部恒星反馈。
Molecular cloud (MC) observations show that clouds have non-thermal velocity dispersions that scale with the cloud size as σ ∝ R1/2 at a constant surface density, and for varying surface density scale with both the cloud’s size and surface density, σ2 ∝ RΣ. The energy source driving these chaotic motions remains poorly understood. We describe the velocity dispersions observed in a cloud population formed in a numerical simulation of a magnetized, stratified, supernova (SN)-driven, interstellar medium, including diffuse heating and radiative cooling, before and after we include the effects of the self-gravity of the gas. We compare the relationships between velocity dispersion, size, and surface density measured in the simulated cloud population to those found in observations of Galactic MCs. Our simulations prior to the onset of self-gravity suggest that external SN explosions alone do not drive turbulent motions of the observed magnitudes within dense clouds. On the other hand, self-gravity induces non-thermal motions as gravitationally bound clouds begin to collapse in our model, approaching the observed relations between velocity dispersion, size, and surface density. Energy conservation suggests that the observed behavior is consistent with the kinetic energy being proportional to the gravitational energy. However, the clouds in our model show no sign of reaching a stable equilibrium state at any time, even for strongly magnetized clouds. We conclude that gravitationally bound MCs are always in a state of gravitational contraction and their properties are a natural result of this chaotic collapse. In order to agree with observed star formation efficiencies, this process must be terminated by the early destruction of the clouds, presumably from internal stellar feedback.
DOI：
10.1051/0004-6361/201321269
发表时间：
2015-04
期刊：
Proceedings of the International Astronomical Union
影响因子：
--
作者：
S. Bihr;H. Beuther;H. Linz;S. Ragan;J. Tackenberg;Rowan J. Smith;T. Henning;O. Krause
通讯作者：
S. Bihr;H. Beuther;H. Linz;S. Ragan;J. Tackenberg;Rowan J. Smith;T. Henning;O. Krause
影响因子：
4.8
作者：
S. Walch;T. Naab
通讯作者：
S. Walch;T. Naab