高z圆盘星系团迁移和吸积生长过程中的定常外流
Steady Outflows in Giant Clumps of High-z Disk Galaxies During Migration and Growth by Accretion
摘要：
我们预测了在高z引力不稳定盘星系中经历恒星驱动外流的巨大团块的演化。我们发现，预计发生的质量损失，通过一个稳定的风超过几十个自由落体时间（t_ff ~ 10万年），而不是由一个或几个t_ff的爆炸性破坏。我们的分析是基于模拟的发现，辐射捕获是可以忽略不计的，因为它使风不稳定（Krumholz & Thompson 2012，2013）。因此，每个光子只能对风的动量贡献一次，所以辐射力被限制在L/c。当结合辐射，原恒星和主序星风，和超新星，我们估计的总动量直接注入流出率为2.5 L/c。超新星和主序星风的绝热阶段可以使这个速率加倍。由此产生的外流质量负载因子是单位阶的，如果这些团块耗尽了它们的气体，时间尺度将是几个盘轨道时间，以恒星中原始团块质量的一半结束。然而，团块迁移到盘中心的时间是轨道时间的顺序，约2.5亿年，所以团块预计将完成其迁移之前耗尽。此外，由于来自盘的吸积和团-团合并，团在盘轨道时间内的质量预计会增加一倍，因此它们的质量实际上会随着时间和半径的减小而增加。从6-7个观测到流出的巨大团块中，有5个与这些预测一致，其中一个具有更高的质量加载因子和动量注入率。后者要么表明，估计的外流是一个高估（1西格玛误差内），SFR已经下降，因为流出时，推出的时间，或驱动机制是不同的，例如超新星反馈产生的腔。
英文摘要：
We predict the evolution of giant clumps undergoing star-driven outflows in high-z gravitationally unstable disk galaxies. We find that the mass loss is expected to occur through a steady wind over many tens of free-fall times (t_ff ~ 10 Myr) rather than by an explosive disruption in one or a few t_ff. Our analysis is based on the finding from simulations that radiation trapping is negligible because it destabilizes the wind (Krumholz & Thompson 2012, 2013). Each photon can therefore contribute to the wind momentum only once, so the radiative force is limited to L/c. When combining radiation, protostellar and main-sequence winds, and supernovae, we estimate the total direct injection rate of momentum into the outflow to be 2.5 L/c. The adiabatic phase of supernovae and main-sequence winds can double this rate. The resulting outflow mass-loading factor is of order unity, and if the clumps were to deplete their gas the timescale would have been a few disk orbital times, to end with half the original clump mass in stars. However, the clump migration time to the disk center is on the order of an orbital time, about 250 Myr, so the clumps are expected to complete their migration prior to depletion. Furthermore, the clumps are expected to double their mass in a disk orbital time by accretion from the disk and clump-clump mergers, so their mass actually grows in time and with decreasing radius. From the 6-7 giant clumps with observed outflows, 5 are consistent with these predictions, and one has a much higher mass-loading factor and momentum injection rate. The latter either indicates that the estimated outflow is an overestimate (within the 1-sigma error), that the SFR has dropped since the time when the outflow was launched, or that the driving mechanism is different, e.g. supernova feedback in a cavity generated by the other feedbacks.
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