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宇宙学模拟中活动星系核射电反馈的影响：盘状星系的形成

The impact of radio feedback from active galactic nuclei in cosmological simulations: Formation of disk galaxies

Takashi Okamoto, Rodrigo S. Nemmen, Richard G. Bower

备注：
22 pages, 16 figures, accepted version for publication in MNRAS, animation available at http://star-www.dur.ac.uk/~takashi/research/movies.html#agn
发表信息：
Mon.Not.Roy.Astron.Soc. 385 (2008) 161-180
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摘要：

在本文中，我们提出了一种新的在星系形成的宇宙学模拟中实现活动星系核（AGN）反馈的方法。我们假设活动星系核产生的喷流能量的一部分作为热能传递给周围的气体。结合质量吸积到黑洞与恒星形成气体的多相描述的理论模型，我们自洽地遵循两个星系和它们的中央黑洞的演化。在我们的模型中的新颖之处是，我们考虑两种不同的吸积模式：标准的辐射有效的薄吸积盘和辐射效率低下的吸积流，我们将一般称为RIAF的理论模型的动机在吸积盘的喷气生产，我们假设只有RIAF是负责AGN的反馈。我们发现，爆炸恒星形成的初始插曲后，吸积率到中央黑洞下降，使吸积盘切换到RIAF结构。在这一点上，来自活动星系核的反馈变得有效，并稍微抑制了星系盘中的恒星形成，几乎完全停止了凸起中的恒星形成。因此，核心成为一个随机燃料的低光度活动星系（塞弗特星系）与周期性的短寿命发作后，恒星爆发。我们的模型预测了低光度活动星系核的一些性质，包括辐射光度、喷流功率、射电喷流对kpc尺度的影响以及活动星系核的寿命，这些结果与Seyfert星系及其射电活动的观测结果基本一致。我们还发现，无论超新星反馈或活动星系核反馈的强度如何，中心黑洞与宿主球体在z = 0处的质量比都约为10^{-3}。（节略）

英文摘要：

In this paper, we present a new implementation of feedback due to active galactic nuclei (AGN) in cosmological simulations of galaxy formation. We assume that a fraction of jet energy, which is generated by an AGN, is transferred to the surrounding gas as thermal energy. Combining a theoretical model of mass accretion onto black holes with a multiphase description of star-forming gas, we self-consistently follow evolution of both galaxies and their central black holes. The novelty in our model is that we consider two distinct accretion modes: standard radiatively efficient thin accretion disks and radiatively inefficient accretion flows which we will generically refer to as RIAFs; motivated by theoretical models for jet production in accretion disks, we assume that only the RIAF is responsible for the AGN feedback. We find that, after an initial episode of bursting star formation, the accretion rate onto the central black hole drops so that the accretion disk switches to a RIAF structure. At this point, the feedback from the AGN becomes efficient and slightly suppresses star formation in the galactic disk and almost completely halts star formation in the bulge. As a result, the nucleus becomes a stochastically fuelled low-luminosity AGN (Seyfert galaxy) with recurrent short-lived episodes of activity after the star bursts. Our model predicts several properties of the low-luminosity AGN including the bolometric luminosity, jet powers, the effect on kpc-scale of the radio jet and the AGN lifetime, which are in broad agreement with observations of Seyfert galaxies and their radio activity. We also find that the mass ratios between the central black hole and the the host spheroid at z = 0 are ~10^{-3} regardless of the strength of either supernova feedback or AGN feedback. (abridged)

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