Dynamical Evolution and Activities in Gas-Rich Galaxies

通过包括星际气体和恒星形成过程在内的数值模拟，研究了富气星系的动力学演化和活动。首先，以银河系、大小麦哲伦云之间的动力学相互作用为例进行了研究。其次，模拟了大椭圆星系和小盘状星系之间的合并。这个研究项目的后半部分集中在星际气体的引力如何影响孤立星系的动力学演化。研究发现，演化早期气体量的大小对非轴对称结构的产生有很大影响，特别是对棒状结构的影响更大。初始气体量本身由盘形成的时间尺度决定。这一结果导致了一个统一的图景，即早期类型星系的条形是由星系-星系相遇产生的，而晚期类型星系的条形是由于盘状星系的引力不稳定而自发形成的。还对原星系的崩塌和随后盘星系的形成进行了模拟。这项研究产生了一种新的演化模型，在该模型中，由于引力不稳定，早期盘中包含的丰富星际气体形成了大量的团块，这些团块充当了演化的主要驱动力。这个模型解释了年轻星系特殊的形态和光度学特征，并为类星体等活动的出现和宿主星系的动力学演化之间的因果关系提供了一幅新的图景。

Dynamical evolution and activities of gas-rich galazies have been investigated by numerical simulations which include interstellar gas and star formation process. First, the dynamical interactions between the Galaxy, Large and Small Magellanic Clouds have been examined as a case study. Second, mergers between large elliptical galaxies and small disk galaxies have been simulated. The second half of this research project has been focused on how the gravity of the interstellar gas affects the dynamical evolution of isolated galaxies. It was found that the amount of the gas existent in the early evolutionary phase strongly affects the occurrence of non-axisymmetric structures, especially bars. The initial gas amount itself is determined by the timescale of disk formation. This result leads to a unified picture that the bars of early-type galaxies have been created by galaxy-galaxy encounters, whereas the late-type galaxies have developed their bars spontaneously by the gravitational instability of the disk. Simulations have been performed also on the collapse of protogalaxies and subsequent formation of disk galaxies. This research resulted into a new evolution model, in which the copious interstellar gas contained in the early disk forms massive clumps due to gravitational instability, and these clumps act as the major driving force of the evolution. This model explains peculiar morphology and photometric characteristics of young galaxies, and provides a new picture on the causal relationship between the emergence of activities such as quasars and the dynamical evolution of host galaxies.