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COLD FRONTS AND GAS SLOSHING IN GALAXY CLUSTERS WITH ANISOTROPIC THERMAL CONDUCTION

机译:具有各向异性热传导的银团簇中的冷前壁和气体逸出

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Cold fronts in cluster cool cores should be erased on short timescales by thermal conduction, unless protected by magnetic fields that are "draped" parallel to the front surfaces, suppressing conduction perpendicular to the sloshing fronts. We present a series of MHD simulations of cold front formation in the core of a galaxy cluster with anisotropic thermal conduction, exploring a parameter space of conduction strengths parallel and perpendicular to the field lines. Including conduction has a strong effect on the temperature distribution of the core and the appearance of the cold fronts. Though magnetic field lines are draping parallel to the front surfaces, preventing conduction directly across them, the temperature jumps across the fronts are nevertheless reduced. The geometry of the field is such that the cold gas below the front surfaces can be connected to hotter regions outside via field lines along directions perpendicular to the plane of the sloshing motions and along sections of the front that are not perfectly draped. This results in the heating of this gas below the front on a timescale of a Gyr, but the sharpness of the density and temperature jumps may nevertheless be preserved. By modifying the gas density distribution below the front, conduction may indirectly aid in suppressing Kelvin-Helmholtz instabilities. If conduction along the field lines is unsuppressed, we find that the characteristic sharp jumps seen in Chandra observations of cold front clusters do not form. Therefore, the presence of cold fronts in hot clusters is in contradiction with our simulations with full Spitzer conduction. This suggests that the presence of cold fronts in hot clusters could be used to place upper limits on conduction in the bulk of the intracluster medium. Finally, the combination of sloshing and anisotropic thermal conduction can result in a larger flux of heat to the core than either process in isolation. While still not sufficient to prevent a cooling catastrophe in the very central (r ~ 5?kpc) regions of the cool core (where something else is required, such as active galactic nucleus feedback), it reduces significantly the mass of gas that experiences a cooling catastrophe outside those small radii.
机译:除非通过平行于前表面“悬垂”的磁场提供保护,否则束状冷却芯中的冷锋应在短时间内通过热传导消除,从而抑制垂直于倾斜前锋的传导。我们提出了一系列各向异性各向异性热传导的星系团核心冷锋形成的MHD模拟,探索了平行于和垂直于磁力线的传导强度的参数空间。包括传导在内,对铁心的温度分布和冷锋的出现都有很大的影响。尽管磁场线平行于前表面悬垂,从而阻止了直接穿过前表面的传导,但仍然减小了前表面的温度跳变。场的几何形状使得前表面下方的冷气可以通过场线沿着垂直于晃动平面的方向并沿着前部未完全披覆的部分连接到外部较热的区域。这导致该气体在Gyr的时间尺度上加热到前下方以下,但是仍然可以保持密度的锐度和温度跃变。通过修改正面下方的气体密度分布,传导可以间接帮助抑制Kelvin-Helmholtz不稳定性。如果沿磁力线的传导没有受到抑制,我们发现在钱德拉观测到的冷锋团簇中不会形成特征性的急剧跳跃。因此,在热星团中冷锋的存在与我们对斯皮策全导通的模拟相矛盾。这表明,热簇中冷锋的存在可以用来在整个簇内介质中设置传导的上限。最后,晃荡和各向异性热传导的组合比隔离的任何一种方法都能导致更大的通向铁心的热通量。虽然仍然不足以防止在冷却核心的中心区域(r〜5?kpc)(需要其他条件,例如活跃的银河核反馈)造成冷却灾难,但它显着降低了经历冷却过程的气体质量。在那些小半径之外冷却灾难。

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