矮星系中的磁化风
Magnetised winds in dwarf galaxies
摘要：
星系间磁场的起源和大小在磁场演化的全球图景中至关重要，因为它被认为是星系磁场和星系团磁场之间在更大尺度上缺失的一环。我们正在测试矮星系是否是解释IGM富集的好候选者：在它们的圆盘形成并触发星系发电机之后，超新星反馈将发射强风，驱逐IGM中的磁场线。我们已经进行了MHD模拟孤立的矮星系，形成自洽内冷却晕。使用RAMSES代码，我们第一次模拟了磁化超新星驱动的星系外流的形成。这种模拟是使用完全宇宙学模拟进行更真实建模的重要一步。我们的模拟很好地再现了观测到的螺旋星系中磁场的性质。模拟盘的形成和演化导致了强磁场放大：末级风泡中的磁场比初始值大一个数量级。圆盘中的磁场基本上是环形的，由于差动旋转而随时间线性增长。我们讨论的后果，这个简单的机制上的宇宙演化的磁场：我们提出了一个新的方案的演化的磁场，矮星系发挥了关键作用，在IGM放大和喷射磁能，导致我们所谓的“宇宙发电机”，可能有助于相当高的磁场强度，今天在星系和星系团。
英文摘要：
The origin and the magnitude of the inter-galactic magnetic field is of primordial importance in the global picture of magnetic field evolution, as it is considered to be the missing link between galactic magnetic fields and cluster magnetic fields on much larger scales. We are testing whether dwarf galaxies are good candidates to explain the enrichment of the IGM: after their discs form and trigger galactic dynamos, supernova feedback will launch strong winds, expelling magnetic field lines in the IGM. We have performed MHD simulations of an isolated dwarf galaxy, forming self-consistently inside a cooling halo. Using the RAMSES code, we have for the first time simulated the formation of a magnetised supernova-driven galactic outflow. This simulation is an important step towards a more realistic modelling using fully cosmological simulations. Our simulations reproduce well the observed properties of magnetic fields in spiral galaxies. The formation and the evolution of our simulated disc lead to a strong magnetic field amplification: the magnetic field in the final wind bubble is one order of magnitude larger than the initial value. The magnetic field in the disc, essentially toroidal, is growing linearly with time as a consequence of differential rotation. We discuss the consequence of this simple mechanism on the cosmic evolution of the magnetic field: we propose a new scenario for the evolution of the magnetic field, with dwarf galaxies playing a key role in amplifying and ejecting magnetic energy in the IGM, resulting in what we call a "Cosmic Dynamo" that could contribute to the rather high field strengths observed in galaxies and clusters today.
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