Dynamical Studies of Molecular Cloud Formation in Spiral Galaxies

AST-0205972 Ostriker几条观测和理论证据表明，巨型分子云（GMC）的寿命很短，在几千万年内形成和分离。主流的理论观点倾向于在螺旋臂中形成GMC的不稳定机制，但现有的工作受到技术限制，并且以前没有直接证明具有GMC性质的凝聚确实形成。 马里兰州大学的Eve Ostriker博士将领导一系列线性稳定性分析、非线性数值模拟和支持诊断的调查，以解决有关螺旋星系中GMC形成的悬而未决的问题。模型将包括几个重要的技术创新。o利用直接数值模拟研究三维帕克不稳定性的发展，通过星系的臂和臂间区域与大尺度密度梯度自洽的真实旋转剪切，还结合自引力研究帕克和吉恩模式的线性和非线性耦合; o利用谱方法、剪切小波积分和磁流体动力学模拟，全面调查星系盘中磁旋转不稳定性的潜在影响，o在自引力和磁驱动星系盘不稳定性的二维和三维模拟中，将一种现实的多相气体介质作为初始条件;直接面对随机凝聚与集体不稳定机制形成GMC-通过在有和没有自引力和磁效应的情况下进行多相演化的受控实验来研究尺度凝聚。由于GMC的形成与星星的形成密切相关，而冷ISM是盘星系中最具动力学响应的组成部分，该项目的成果将对银河系和河外天文学研究产生广泛的影响，对理解星星形成的全球规律和哈勃序列中螺旋星系的结构和演化具有重要意义。

AST-0205972OstrikerSeveral lines of observational and theoretical evidence suggest that giant molecular clouds (GMCs) have short lifetimes, forming and dissociating within a few tens of millions of years. Prevailing theoretical arguments favor instability mechanisms in spiral arms to form GMCs, but existing work has suffered from technical limitations, and has not previously directly demonstrated that condensations with the properties of GMCs indeed form. Dr. Eve Ostriker, at the University of Maryland, will lead an investigation of a series of linear stability analyses, nonlinear numerical simulations, and supporting diagnostics to address outstanding questions concerning GMC formation in spiral galaxies. The modeling will include several important technical innovations. These researchers will, for the first time:o Use direct numerical simulations to study development of the Parker instability in 3D with realistic rotational shear self-consistent with large-scale density gradients through arm and interarm regions of galaxies, also incorporating self-gravity to study linear and nonlinear coupling of Parker and Jeans modes;o Comprehensively survey, using spectral methods, shearing-wavelet integrations, and magneto-hydrodynamic (MHD) simulations, the potential effects of the magnetorotational instability in galactic disks, focusing on coupling to self-gravitating modes in both secular-growth and saturated-state regimes;o Incorporate a realistic multi-phase gaseous medium for the initial conditions in two and three- dimensional simulations of self-gravitating and magnetically-driven galactic disk instabilities;o Directly confront stochastic coagulation vs. collective instability mechanisms for forming GMC-scale condensations by performing controlled experiments of multiphase evolution with and without self-gravity and magnetic effects.As GMC formation is intimately coupled to star formation, and the cold ISM is the most dynamically-responsive component of a disk galaxy, the results of this project will have broad impacts on both Galactic and extragalactic astronomical research, with implications for understanding the global regulation of star formation and the structure and evolution of spiral galaxies across the Hubble sequence.***