湍流多相流ISM中的压力关系和垂直平衡
Pressure Relations and Vertical Equilibrium in the Turbulent, Multiphase ISM
摘要：
我们使用的湍流，多相，自引力气体模型盘星系轨道的数值模拟研究压力，垂直气体分布，和密度扩散气体的比例之间的关系。我们表明，磁盘的高度和平均中面压力是一致的有效流体静力平衡，提供了湍流的垂直速度色散和气体自重。质量加权压力比中平面压力高一个数量级，因为自重力集中了气体并增加了云中的压力。我们还研究了Rmol=M（H2）/M（H1）的比值。Blitz和Rosolowsky（2006）表明，Rmol与估计的中平面压力成正比。对于模型系列中的周转频率，卡帕，和气体表面密度，西格玛，成比例，我们恢复的经验关系。对于kappa和Sigma独立的其他模型系列，中平面压力和Rmol相关性不好。我们的结论是，分子分数-和恒星形成率-星系盘固有地取决于它的旋转状态，而不仅仅是本地值的西格玛和恒星密度ρ *。Rmol和中平面压力之间的经验相关性意味着“环境参数”Kappa，Sigma和rho* 在真实星系中是相互依赖的，可能是由于Toomre Q接近统一的状态演变的结果。我们注意到，Rmol在静态模型中远远超过我们的湍流模拟和观测值的值，这意味着湍流是至关重要的，以获得一个现实的分子分数在ISM。
英文摘要：
We use numerical simulations of turbulent, multiphase, self-gravitating gas orbiting in model disk galaxies to study the relationships among pressure, the vertical gas distribution, and the ratio of dense to diffuse gas. We show that the disk height and mean midplane pressure are consistent with effective hydrostatic equilibrium, provided that the turbulent vertical velocity dispersion and gas self-gravity are included. Mass-weighted pressures are an order of magnitude higher than the midplane pressure because self-gravity concentrates gas and increases the pressure in clouds. We also investigate the ratio Rmol=M(H2)/M(HI) for our simulations. Blitz and Rosolowsky (2006) showed that Rmol is proportional to the estimated midplane pressure. For model series in which the epicyclic frequency, kappa, and gas surface density, Sigma, are proportional, we recover the empirical relation. For other model series in which kappa and Sigma are independent, the midplane pressure and Rmol are not well correlated. We conclude that the molecular fraction -- and star formation rate -- of a galactic disk inherently depends on its rotational state, not just the local values of Sigma and the stellar density rho*. The empirical correlation between Rmol and midplane pressure implies that the "environmental parameters" kappa, Sigma, and rho* are interdependent in real galaxies, presumably as a consequence of evolution toward states with Toomre Q near unity. We note that Rmol in static models far exceeds both the values in our turbulent simulations and observed values, implying that turbulence is crucial to obtaining a realistic molecular fraction in the ISM.
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