在高红移星系中观测到的活动星系核与剧烈盘不稳定性之间的联系
An Observed Link between Active Galactic Nuclei and Violent Disk Instabilities in High-Redshift Galaxies
摘要：
我们提供的证据之间的相关性存在的巨大团块和活动星系核（AGN）的盘星系。10^8-9兆太阳质量的巨大团块来自于富含气体的星系中剧烈的引力不稳定性，有人提出这种不稳定性可以为超大质量黑洞（BH）提供能量。我们使用发射线诊断比较样本的14个cloudies（不稳定）磁盘和样本的13个平滑（稳定）磁盘在红移z~0.7。在我们的样本中，大部分的星团盘有很高的概率包含活动星系核。它们的[OIII]发射线被强烈激发，与低金属量恒星形成不一致。[NeIII]激发也更高。稳定磁盘很少有这样的属性。叠加超灵敏的钱德拉观测（4 M）揭示了在cluerous星系中的X射线过剩，这不能仅仅是由于恒星形成，并证实了AGN的存在。在我们的中红移样本中的cluerous星系具有典型的富气盘星系的性质，而不是合并，特别是在恒星形成的主序列上。这表明，我们的研究结果适用于物理上相似的和众多的富含气体的不稳定盘在z>1。利用观测到的[OIII]和X射线光度，我们保守地估计，活动星系核的主盘具有典型的辐射热光度，大约为10^43 erg/s，BH的增长率约为10^-2 Msun/yr，而且这些活动星系核在X射线中基本上是模糊的。这种中等光度模式可能足以在几个Gyr上提供今天BH质量的很大一部分，因为我们的观测表明占空比很高（>10%），在较短的阶段内可能发生具有较高光度的吸积爆发。观测到的盘不稳定性随质量和红移的演化可以解释恒星形成和BH生长的同时缩小。
英文摘要：
We provide evidence for a correlation between the presence of giant clumps and the occurrence of active galactic nuclei (AGN) in disk galaxies. Giant clumps of 10^8-9 Msun arise from violent gravitational instability in gas-rich galaxies, and it has been proposed that this instability could feed supermassive black holes (BH). We use emission line diagnostics to compare a sample of 14 clumpy (unstable) disks and a sample of 13 smoother (stable) disks at redshift z~0.7. The majority of clumpy disks in our sample have a high probability of containing AGN. Their [OIII] emission line is strongly excited, inconsistent with low-metallicity star formation alone. [NeIII] excitation is also higher. Stable disks rarely have such properties. Stacking ultra sensitive Chandra observations (4 Ms) reveals an X-ray excess in clumpy galaxies, which cannot be solely due to star formation and confirms the presence of AGN. The clumpy galaxies in our intermediate-redshift sample have properties typical of gas-rich disk galaxies rather than mergers, being in particular on the Main Sequence of star formation. This suggests that our findings apply to the physically-similar and numerous gas-rich unstable disks at z>1. Using the observed [OIII] and X-ray luminosities, we conservatively estimate that AGN hosted by clumpy disks have typical bolometric luminosities of the order of a few 10^43 erg/s, BH growth rates ~10^-2 Msun/yr, and that these AGN are substantially obscured in X-rays. This moderate-luminosity mode could be sufficient to provide a large fraction of today's BH mass over a couple of Gyr given that our observations suggest a high duty cycle (>10%), accretion bursts with higher luminosities being possible over shorter phases. The observed evolution of disk instabilities with mass and redshift could explain the simultaneous downsizing of star formation and of BH growth.
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