模拟超大质量黑洞的增长：改进的次网格公式
Modelling supermassive black hole growth: towards an improved sub-grid prescription
摘要：
在星系形成的模拟中，超大质量黑洞的吸积过程经常采用Bondi-Hoyle模型。在这里，我们研究这种方法的有效性分析和数值。我们认为，字符的流动，其中一个评估的气体性质是不可能满足简单的邦迪-霍伊尔模型。只有在特定的情况下，热维里化的气体与零角动量和可忽略的辐射冷却是邦迪-霍伊尔解决方案有关。在另一个极端中，由于有效的冷却和周围晕的主导重力，气体在评估半径处处于自由落体状态，邦迪-霍伊尔形式主义在任何一个方向上都可能是错误的。这可能会在宇宙学模拟中对晕质量施加人为的趋势，因为不同的晕质量会有不同的因素。我们提出了一个表达式的次网格吸积率之间的自由落体制度和邦迪-霍伊尔制度，因此考虑到的贡献晕的气体动力学。
英文摘要：
Accretion onto supermassive black holes (SMBHs) in galaxy formation simulations is frequently modelled by the Bondi-Hoyle formalism. Here we examine the validity of this approach analytically and numerically. We argue that the character of the flow where one evaluates the gas properties is unlikely to satisfy the simple Bondi-Hoyle model. Only in the specific case of hot virialised gas with zero angular momentum and negligible radiative cooling is the Bondi-Hoyle solution relevant. In the opposite extreme, where the gas is in a state of free-fall at the evaluation radius due to efficient cooling and the dominant gravity of the surrounding halo, the Bondi-Hoyle formalism can be erroneous by orders of magnitude in either direction. This may impose artificial trends with halo mass in cosmological simulations by being wrong by different factors for different halo masses. We propose an expression for the sub-grid accretion rate which interpolates between the free-fall regime and the Bondi-Hoyle regime, therefore taking account of the contribution of the halo to the gas dynamics.
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