盛宴与饥饿：低红移星系中黑洞生长的调控
Feast and Famine: Regulation of Black Hole Growth in Low Redshift Galaxies
摘要：
我们分析了观测到的分布爱丁顿比作为超大质量黑洞质量的函数的附近星系的大样本从斯隆数字巡天。我们证明了在邻近星系中有两种不同的黑洞生长机制。第一个是与在其中央千秒差距区域有显著恒星形成的星系有关，其特征是吸积率呈广泛的对数正态分布，峰值约为爱丁顿极限的1%。在这个制度下，爱丁顿比分布是独立的质量的黑洞，并显示没有进一步依赖于中央恒星星族的星系。第二个制度是与星系的老中央恒星星族，其特点是由幂律分布函数的爱丁顿比。在这种情况下，黑洞的时间平均质量吸积率与星系核中恒星的质量成正比，比例常数取决于恒星的平均年龄。这个结果再次与黑洞质量无关。我们发现，无论是斜率的幂律和吸积率下降到黑洞在老星系是一致的人口合成模型预测的恒星质量损失率下降的函数平均恒星年龄。我们的结果导致一个非常简单的黑洞在本地宇宙的增长图片。如果星系核球中的冷气体供应充足，黑洞会调节自己的生长速度，使其不再依赖于星际介质的性质。一旦气体耗尽，黑洞的增长就受到演化恒星失去质量的速度的调节。
英文摘要：
We analyze the observed distribution of Eddington ratios as a function of supermassive black hole mass for a large sample of nearby galaxies drawn from the Sloan Digital Sky Survey. We demonstrate that there are two distinct regimes of black hole growth in nearby galaxies. The first is associated with galaxies with significant star formation in their central kiloparsec regions, and is characterized by a broad log-normal distribution of accretion rates peaked at about one percent of the Eddington limit. In this regime, the Eddington ratio distribution is independent of the mass of the black hole and shows no further dependence on the central stellar population of the galaxy. The second regime is associated with galaxies with old central stellar populations, and is characterized by a power-law distribution function of Eddington ratios. In this regime, the time-averaged mass accretion rate onto black holes is proportional to the mass of stars in the galaxy bulge, with a constant of proportionality that depends on the mean stellar age of the stars. This result is once again independent of black hole mass. We show that both the slope of the power-law and the decrease in the accretion rate onto black holes in old galaxies are consistent with population synthesis model predictions of the decline in stellar mass loss rates as a function of mean stellar age. Our results lead to a very simple picture of black hole growth in the local Universe. If the supply of cold gas in a galaxy bulge is plentiful, the black hole regulates its own growth at a rate that does not further depend on the properties of the interstellar medium. Once the gas runs out, black hole growth is regulated by the rate at which evolved stars lose their mass.
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