$z\sim 2$三重类星体合并形成的超大质量黑洞
Ultramassive black holes formed by triple quasar mergers at $z\sim 2$
摘要：
罕见而难以捉摸的超大质量黑洞（UMBH，MBH > 1 e 10 Msun）的起源是一个悬而未决的问题。利用大体积宇宙流体动力学模拟ASTRID，我们报道了一个极大质量的UMBH的形成，MBH ~ 1 e11 Msun在z~2。UMBH是由两个恒星质量M* > 3e 11 Msun的大质量星系连续合并而成的，它们也产生了一个明亮而罕见的三重类星体系统，由三个~10^9 Msun的黑洞提供动力。超大质量黑洞（SMBH）的第二次合并是在1.5亿年后的第一次合并之后。合并事件导致中央SMBH上持续的爱丁顿吸积，在M* > 2 e12 Msun的大质量致密恒星核中心形成UMBH。UMBH的强烈反馈将周围的恒星形成淬灭到内部50 kpc/h区域的< 10 Msun/yr。在ASTRID中还有两个在z>2处MBH > 5e 10 Msun的UMBH也是由星系合并产生的，它们的祖先可以作为低光度的类星体三联体被观测到。很少被观测到的类星体多重体可能是高红移的UMBH的摇篮，并可能最终位于最大质量星系团的中心。
英文摘要：
The origin of rare and elusive ultramassive black holes (UMBH, with MBH > 1e10 Msun) is an open question. Using the large volume cosmological hydrodynamic simulation ASTRID, we report on the formation of an extremely massive UMBH with MBH ~ 1e11 Msun at z~2. The UMBH is assembled as a result of two successive mergers of massive galaxies each with stellar mass M* > 3e11 Msun that also produces a bright, rare triple quasar system powered by three ~10^9 Msun black holes. The second merger of supermassive black holes (SMBHs) follows the first after 150 Myrs. The merger events lead to sustained Eddington accretion onto the central SMBH, forming an UMBH in the center of a massive compact stellar core with M* > 2e12 Msun. The strong feedback of the UMBH quenches the surrounding star formation to < 10 Msun/yr in the inner 50 kpc/h region. There are two more UMBHs with MBH > 5e10 Msun at z>2 in ASTRID which are also produced by major mergers of galaxies, and their progenitors can be observed as quasar triplets of lower luminosity. The rarely observed quasar multiples can be the cradle of UMBHs at high redshift, and likely end up in the center of the most massive clusters.
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