气体能阻止小合并对薄星盘的破坏吗？
Can Gas prevent the Destruction of Thin Stellar Discs by Minor Mergers?
摘要：
我们研究了盘星系在小合并过程中耗散气体物理对垂直加热和增厚的影响。我们产生了一套轻微的合并模拟银河系类星系。该套件包括无碰撞模拟以及流体动力学运行，包括银河系盘中的气体成分。我们发现，在无耗散模拟轻微合并导致磁盘的规模高度增加到一个因素~2。当考虑到盘中存在气体时，对于20%（40%）的初始盘气体分数，该增厚减少了25%（50%），导致在0.6和0.7kpc之间的最终刻度高度z 0，而与初始刻度高度无关。我们认为，气体的存在减少磁盘加热通过两种机制：吸收动能的气体和/或形成一个新的薄恒星盘，可以导致加热的恒星向盘平面重新收缩的冲击能量。我们表明，在我们的模拟中，大部分的气体被消耗在合并过程中，因此，一个新的薄盘的再生有一个可以忽略不计的影响合并后的星系的z 0。在我们的模拟中发现的最终盘标度高度与螺旋星系垂直结构的研究非常一致，其中大多数系统的标度高度为0.4 kpc <z 0 < 0.8 kpc。我们还发现，最近对银河系薄盘的尺度高度的测量与我们的流体动力学模拟结果之间没有紧张关系。我们的结论是，在银河系和外部星系薄盘的存在是不明显的冲突与CDM模型的预测。
英文摘要：
We study the effect of dissipational gas physics on the vertical heating and thickening of disc galaxies during minor mergers. We produce a suite of minor merger simulations for Milky Way-like galaxies. This suite consists of collisionless simulations as well as hydrodynamical runs including a gaseous component in the galactic disc. We find that in dissipationless simulations minor mergers cause the scale height of the disc to increase by up to a factor of ~2. When the presence of gas in the disc is taken into account this thickening is reduced by 25% (50%) for an initial disc gas fraction of 20% (40%), leading to a final scale height z0 between 0.6 and 0.7 kpc, regardless of the initial scale height. We argue that the presence of gas reduces disc heating via two mechanisms: absorption of kinetic impact energy by the gas and/or formation of a new thin stellar disc that can cause heated stars to recontract towards the disc plane. We show that in our simulations most of the gas is consumed during the merger and thus the regrowth of a new thin disc has a negligible impact on the z0 of the post merger galaxy. Final disc scale heights found in our simulations are in good agreement with studies of the vertical structure of spiral galaxies where the majority of the systems are found to have scale heights of 0.4 kpc < z0 < 0.8 kpc. We also found no tension between recent measurements of the scale height of the Milky Way thin disc and results coming from our hydrodynamical simulations. We conclude that the existence of a thin disc in the Milky Way and in external galaxies is not in obvious conflict with the predictions of the CDM model.
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