Ram Pressure如何驱动存活星系盘中的径向气体运动
How Ram Pressure Drives Radial Gas Motions in the Surviving Disk
AI总结：
本研究通过高分辨率风洞流体动力学模拟，发现ram压力剥离会通过介质混合与压力扭矩增强驱动星系中心气体内流，同时指出现有黑洞吸积估算模型的不足，提出需构建新模型。
摘要：
星系演化会受到环境的显著影响，尤其是星系团的致密环境。近期观测研究表明，经历强ram pressure stripping（RPS， ram压力剥离）的大质量星系，其核活动出现的频率也有所升高。本文中，我们利用一组风洞流体动力学模拟对这一课题展开研究，模拟对象为单个恒星质量$M_\text{star} = 10^{11} M_\odot$的大质量盘星系，分辨率达39秒差距，同时纳入了恒星形成与恒星反馈过程。我们发现，无论风的冲击角度如何，RPS都会增加向星系中心的气体内流。这种内流增强由两方面驱动：一是在所有风入射角下，星际介质与无转动的星系团内介质（ICM）发生混合；二是内盘气体受到的扭矩增大，当ICM风存在侧向（edge-on）分量时，这种扭矩主要来自局地压力梯度。而压力扭矩的增大，又是由ram压力梯度的升高所驱动的。我们采用Bondi-Hoyle模型与扭矩模型估算了黑洞（BH）的吸积率，并将其与中心140秒差距区域的质量通量进行对比。结果发现，对于经历RPS的星系，扭矩模型估算出的黑洞吸积量远低于Bondi-Hoyle估算值。但我们认为这两种模型都存在局限性：常用的扭矩模型未考虑气体分布或局地压力梯度产生的扭矩，而Bondi-Hoyle估算值依赖于热气体的声速——在被剥离的星系中，热气体包含了ICM成分，因此需要构建新的估算模型。
英文摘要：
Galaxy evolution can be dramatically affected by the environment, especially by the dense environment of a galaxy cluster. Recent observational studies show that massive galaxies undergoing strong ram pressure stripping (RPS) also show an enhanced frequency of nuclear activity. Here, we investigate this topic using a suite of wind-tunnel hydrodynamical simulations of an individual massive $M_\text{star} = 10^{11} M_\odot$ disk galaxy with 39 pc resolution and including star formation and stellar feedback. We find that RPS increases the inflow of gas to the galaxy centre regardless of the wind impact angle. This increase is driven by the mixing of interstellar and non-rotating intracluster media at all wind angles, and by increased torque on the inner disk gas, mainly from local pressure gradients when the ICM wind has an edge-on component. In turn, the increase in pressure torques is driven by rising gradient of ram pressure. We estimate the black hole (BH) accretion using Bondi-Hoyle and torque models, and compare it with the mass flux in the central 140 pc region. We find that the torque model estimates much less accretion onto the BH of a RPS galaxy than the Bondi-Hoyle estimator. However, we argue that both models are incomplete because the commonly used torque model does not account for torques caused by the gas distribution or local pressure gradients and the Bondi-Hoyle estimator depends on the the sound speed of the hot gas, which includes the ICM in stripped galaxies, thus a new estimator would be required.
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