Magnetic field amplification and star bursts induced by mergers of disk galaxies

我们计划通过数值模拟的方法来探索盘状星系合并过程中磁场的演化、恒星的形成活动和分子气体。理论和观测研究都表明，合并在星系的演化中起着重要的作用，并且在合并过程中有磁场放大的迹象。基于没有暗物质晕的绝热气体盘的初步数值模拟，我们提出了一个实质上更现实的星系合并模型，通过引入暗物质晕模型的粒子，更详细的化学反应处理，特别是分子氢的形成，以及包含湍流，恒星形成和反馈的亚网格物理。我们将使用磁流体动力学自适应网格细化代码Enzo，包括一个新的磁流体动力学湍流亚网格尺度模型和天体化学包KROME，以比以前的星系模拟更详细地模拟分子气体的形成。此外，我们将应用一个恒星形成的动力学模型，该模型不是基于与观测到的孤立星系的kennicut - schmidt关系相对应的固定效率参数。该方法已成功地应用于无磁场的孤立盘状星系的模拟中，模型重现了正确的效率。在这个项目中，我们将把模型扩展到磁流体动力学的情况下，在孤立的磁盘模拟中进行测试，然后将其应用于合并。概述的方法将使我们能够揭示不同的湍流产生通道对磁场放大的影响（基本上是不稳定性与反馈），对合并参数（如磁盘方向和冲击参数）的依赖，以及合并系统中恒星形成与分子气体含量之间的关系。

We plan to explore the evolution of the magnetic field, the star formation activity, and the molecular gas during mergers of disk galaxies by means of numerical simulations. Both theoretical and observational studies showed that mergers play a significant role in the evolution of galaxies and there are indications of magnetic field amplification during mergers. Based on preliminary numerical simulations of adiabatic gaseous disks without dark matter halos, we propose a substantially more realistic model of galaxy mergers by introducing dark-matter halos modelled be particles, a more detailed treatment of chemical reactions, particularly the formation of molecular hydrogen, and subgrid physics encompassing turbulence, star formation, and feedback. We will employ the magnetohydrodynamical adaptive mesh refinement code Enzo, including a novel subgrid-scale model for magnetohydrodynamical turbulence and the astrochemistry package KROME to model the formation of molecular gas in greater detail than in previous galaxy simulations. Moreover, we will apply a dynamical model of star formation that is not based on a fixed efficiency parameter corresponding to the observed Kennicutt-Schmidt relation for isolated galaxies. This approach was successfully applied in simulations of isolated disk galaxies without magnetic fields, for which the correct efficiency is reproduced by the model. In this project, we will extend the model to the magnetohydrodynamical case, test it in isolated disk simulations and then apply it to mergers. The outlined methodology will allow us to unravel the impact of different channels of turbulence production on magnetic field amplification (basically instabilities vs feedback), the dependence on merger parameters such as disk orientation and impact parameter, and the relation between star formation and molecular gas content in merging systems.