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arXiv 0903.0387astro-ph.GA
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椭圆星系和星系团中动力学和热AGN反馈的可观测结果

Observable consequences of kinetic and thermal AGN feedback in elliptical galaxies and galaxy clusters

Edward C. D. Pope

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Accepted for publication in MNRAS, 11 pages, 2 figures and 2 tables
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摘要：

我们建立了活动星系核反馈的解析模型，并研究了它对椭圆星系和星系团的意义。结果表明，当动量注入超过临界值时，低质量椭圆星系中的物质将被喷射出来，并产生X射线光度$L_{\rm X}$，即$\propto$ $σ^{8-10}$，这取决于活动星系核的加燃料机制，其中$σ$是热气体的速度色散。这一结果与观测结果和半解析模型吻合得很好。在更大质量的椭圆星系和星系团中，活动星系核外流很快变成浮力主导的。这必然意味着，由中心星系团活动星系核加热的星系团内介质（ICM）重新分布，使得在冷却半径内的热气体质量应该是$ \propto L_{\rm X}(<r_{\rm cool})/[g(r_{\rm cool})σ]$，其中$g(r_{\rm cool})$是冷却半径处的重力加速度。这一预测得到了证实，使用七个集群的观察。同样的机制也定义了$\sim 0.5$ Gyr的临界ICM冷却时间，这与最近的观测结果相一致，表明恒星形成和活动星系核活动在低于通用冷却时间阈值时被触发。

英文摘要：

We have constructed an analytical model of AGN feedback and studied its implications for elliptical galaxies and galaxy clusters. The results show that momentum injection above a critical value will eject material from low mass elliptical galaxies, and leads to an X-ray luminosity, $L_{\rm X}$, that is $\propto$ $σ^{8-10}$, depending on the AGN fuelling mechanism, where $σ$ is the velocity dispersion of the hot gas. This result agrees well with both observations and semi-analytic models. In more massive ellipticals and clusters, AGN outflows quickly become buoyancy-dominated. This necessarily means that heating by a central cluster AGN redistributes the intracluster medium (ICM) such that the mass of hot gas, within the cooling radius, should be $ \propto L_{\rm X}(<r_{\rm cool})/[g(r_{\rm cool})σ]$, where $g(r_{\rm cool})$ is the gravitational acceleration at the cooling radius. This prediction is confirmed using observations of seven clusters. The same mechanism also defines a critical ICM cooling time of $\sim 0.5$ Gyr, which is in reasonable agreement with recent observations showing that star formation and AGN activity are triggered below a universal cooling time threshold.

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