AGN feedback and multiphase gas in giant elliptical galaxies
AGN feedback and multiphase gas in giant elliptical galaxies
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DOI：
10.1093/mnras/sty2906
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发表时间：
2018-05
影响因子：
4.8
通讯作者：
Chaoran Wang;Yuan Li;M. Ruszkowski
中科院分区：
文献类型：
--
作者：
Chaoran Wang;Yuan Li;M. Ruszkowski
最近的观测发现，在很大一部分大质量椭圆星系中存在延伸的多相气体。为了研究热不稳定性的发展和多相结构的形成，我们对两个理想的椭圆星系进行了高分辨率的三维流体动力学模拟——一个代表了一个典型的星系，其初始条件有利于热不稳定性的发展，另一个则不太可能发展热不稳定性。我们分析了辐射冷却、动量驱动的AGN反馈、恒星形成以及来自年轻和年老恒星的恒星反馈之间的相互作用。我们发现在一类椭圆星系中，热晕气体的熵作为半径的函数急剧上升，热晕是热稳定的，失控冷却只能发生在星系的最中心。在其他类型的椭圆中，热晕气体的冷却时间与自由落体时间之比接近10，并且由AGN反馈驱动的非线性扰动会导致热晕气体频繁析出延伸的多相细丝。多相和单相椭圆星系都经历了由冷却驱动的AGN反馈循环。有趣的是，AGN反馈保持了晕的多相或单相性质，但不会将多相星系变成单相星系，反之亦然。多相星系中一些延伸的冷气体也形成了年轻的恒星。恒星形成的水平及其空间分布与哈勃对附近椭圆星系的观测结果非常吻合。
Recent observations have found extended multi-phase gas in a significant fraction of massive elliptical galaxies. We perform high-resolution three-dimensional hydrodynamical simulations of two idealized elliptical galaxies -- one representing a typical galaxy characterized by initial conditions conducive to the development of thermal instability and the other one less likely to develop thermal instability -- in order to study the development of thermal instability and the formation of multi-phase structures. We analyze the interplay between radiative cooling, momentum-driven AGN feedback, star formation, and stellar feedback from both young and old stars. We find that in one class of elliptical galaxies, the entropy of the hot halo gas rises sharply as a function of radius, and the hot halo is thermally stable and run-away cooling can only happen in the very center of the galaxy. In other class of ellipticals, the hot halo gas has a cooling to free-fall time ratio close to 10, and the non-linear perturbation driven by AGN feedback can cause the hot gas to frequently precipitate into extended multi-phase filaments. Both multi- and single-phase elliptical galaxies experience cooling-driven AGN feedback cycles. Interestingly, AGN feedback maintains the multi- or single-phase nature of the halo but does not turn multi-phase galaxies into single-phase ones or vice versa. Some of the extended cold gas in the multi-phase galaxy also forms young stars. The level of star formation and its spatial distribution are in excellent agreement with {\it Hubble} observations of nearby elliptical galaxies.