The mass ratio distribution of MBH binaries in the hierarchical model

作     者：Sheng-Nian Xu Ye-Fei Yuan Jing-Meng Hao Ning-Yu Tang 

作者机构：Key Laboratory for Research in Galaxies and Cosmology University of Science and Technology of China Chinese Academy of Sciences Academy of Mathematics and Systems Science Chinese Academy of Sciences 

出 版 物：《Research in Astronomy and Astrophysics》 (天文和天体物理学研究（英文版）)

年 卷 期：2015年第15卷第6期

页      面：773-784页

核心收录：

学科分类：07[理学] 070401[理学-天体物理] 0704[理学-天文学] 

基　　金：Supported by the National Natural Science Foundation of China 

主　　题：cosmology theory -- black hole physics -- galaxies interaction 

摘      要：We present different mass ratio distributions of massive black hole （MBH） binaries due to different mechanisms involved in binary evolution. A binary system of MBHs forms after the merger of two galaxies, which has three stages： the dynamical friction stage, the stellar scattering or circumbinary disk stage, and the gravitational radiation stage. The second stage was once believed to be the ＂final parsec problem＂ （FPP） as the binary stalled at this stage because of the depletion of stars. Now, the FPP has been shown to no longer be a problem. Here we get two different mass ratio distributions of MBH binaries under two mechanisms, stellar scattering and the cir- cumbinary disk interaction. For the circumbinary disk mechanism, we assume that the binary shrinks by interaction with a circumbinary disk and the two black holes （BHs） have different accretion rates in the simulation. We apply this simple assumption to the hierarchical coevolution model of MBHs and dark matter halos, and we find that there will be more equal-mass MBH binaries in the final coalescence for the case where the circumbinary mechanism operates. This is mainly because the secondary BH in the circumbinary disk system accretes at a higher rate than the primary one.