arXiv 1801.096992018-01astro-ph.GA

无膨胀星系中的正常黑洞：宇宙时间内黑洞的大部分静止、无合并增长

Normal black holes in bulge-less galaxies: the largely quiescent, merger-free growth of black holes over cosmic time

G. Martin, S. Kaviraj, M. Volonteri, B. D. Simmons, J. E. G. Devriendt, C. J. Lintott, R. J. Smethurst, Y. Dubois, C. Pichon

备注：: 12 pages, 9 figures, accepted for publication in MNRAS
DOI：: 10.1093/mnras/sty324

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摘要：

理解黑洞形成的驱动过程是观测宇宙学的一个关键课题。虽然观测到的$M_{\mathrm{BH}}$ - $M_{\mathrm{Bulge}}$相关性在膨胀为主的星系被认为是产生的主要合并，一个$M_{\mathrm{BH}}$ -$M_{\star}$关系的存在，在所有的星系形态类型，表明BH可能主要是由长期的过程。最近的证据表明，没有膨胀的星系，不太可能有重大的合并，是从$M_{\mathrm{BH}}$ - $M_{\mathrm{Bulge}}$关系的偏移，但躺在$M_{\mathrm{BH}}$ - $M_{\star}$关系，加强了这一假设。然而，目前数据集的小尺寸和异质性，加上难以测量精确的BH质量，使得仅使用经验研究来解决这个问题具有挑战性。在这里，我们使用地平线活动星系核，宇宙学流体动力学模拟探索的作用，合并在宇宙时间的BH增长。结果表明：（1）与观测结果一致，模拟的无球星系偏离了主$M_{\mathrm{BH}}$ - $M_{\mathrm{Bulge}}$关系，但偏离了主$M_{\mathrm{BH}}$- $M_{\star}$关系;（2）星系在$M_{\mathrm{BH}}$ - $M_{\star}$关系中的位置不受星系合并历史的影响;在今天的大质量星系中，只有$\sim$ 35%的BH质量是直接归因于合并的--大多数因此，BH的增长（$\sim$ 65%）是在宇宙时间内通过长期过程逐渐发生的。

英文摘要：

Understanding the processes that drive the formation of black holes (BHs) is a key topic in observational cosmology. While the observed $M_{\mathrm{BH}}$--$M_{\mathrm{Bulge}}$ correlation in bulge-dominated galaxies is thought to be produced by major mergers, the existence of a $M_{\mathrm{BH}}$--$M_{\star}$ relation, across all galaxy morphological types, suggests that BHs may be largely built by secular processes. Recent evidence that bulge-less galaxies, which are unlikely to have had significant mergers, are offset from the $M_{\mathrm{BH}}$--$M_{\mathrm{Bulge}}$ relation, but lie on the $M_{\mathrm{BH}}$--$M_{\star}$ relation, has strengthened this hypothesis. Nevertheless, the small size and heterogeneity of current datasets, coupled with the difficulty in measuring precise BH masses, makes it challenging to address this issue using empirical studies alone. Here, we use Horizon-AGN, a cosmological hydrodynamical simulation to probe the role of mergers in BH growth over cosmic time. We show that (1) as suggested by observations, simulated bulge-less galaxies lie offset from the main $M_{\mathrm{BH}}$--$M_{\mathrm{Bulge}}$ relation, but on the $M_{\mathrm{BH}}$--$M_{\star}$ relation, (2) the positions of galaxies on the $M_{\mathrm{BH}}$--$M_{\star}$ relation are not affected by their merger histories and (3) only $\sim$35 per cent of the BH mass in today's massive galaxies is directly attributable to merging -- the majority ($\sim$65 per cent) of BH growth, therefore, takes place gradually, via secular processes, over cosmic time.

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