红星系中存在H α宽变的局部活动星系核
Local Active Galactic Nuclei with Large Broad-Hα Variability Reside in Red Galaxies
摘要：
我们在寻找中等质量黑洞的过程中，偶然发现了6个具有不同宽Halpha通量的活动星系核，受到这些发现的启发，我们对变貌活动星系核和大变率活动星系核进行了系统的研究。我们收集了所有z<0.15的CL活动星系核和混响映射的活动星系核，并对其图像和光谱进行了仔细的分解拟合。我们发现了两个观测事实：（1）本地CL和大变活动星系核的宿主星系，主要是Seyfert星系，位于一般Seyfert星系群的红尾（贫气体）。(2)相比之下，有一个显着的趋势，他们更明亮的对应物，即CL和极变类星体（CLQ和EVQ）是不同的：CLQ通常在蓝色星系中;在SFR和M* 图中，本地CL塞弗特星系位于绿谷，而CLQ宿主位于恒星形成的主序列中。我们提出的解释，这些强可变的Seyferts和类星体，分别根据吸积盘广泛依赖于核燃料模式的思想。局部大变率和CL Seyferts处于核饥荒模式，其中冷气团可以在燃料流中随机形成，并且它们的偶发性下降在吸积率曲线中产生尖峰。CLQ和EVQ处于盛宴加油模式，这可能解释了它们对蓝色星系的偏好和它们的变化模式（连续分布的高振幅尾部）。最后，我们提出了一种新的思路：利用光学变率在红星系中寻找IMBH。
英文摘要：
Inspired by our serendipitous discovery of six AGNs with varying broad-Halpha fluxes over years out of our searching for intermediate-mass black holes (IMBHs), we conduct a systematic investigation of changing-look (CL) and large-variability AGNs. We collect all the CL AGNs at z<0.15 and the reverberation mapped AGNs with strongly variable broad Halpha, and perform careful decomposition fittings to both their images and spectra. We find two observational facts: (1) The host galaxies of local CL and large-variability AGNs, mainly being Seyferts, are in the red (gas-poor) tail of the general Seyfert galaxy population. (2) In contrast, there is a significant trend that their more luminous counterparts namely CL and extremely variable quasars (CLQs and EVQs) are different: CLQs are generally in blue galaxies; in terms of the diagram of SFR and M* local CL Seyfert galaxies are located in the green valley, whereas CLQ hosts are in the star-forming main sequence. We propose explanations for those strongly variable Seyferts and quasars, respectively, under the thought that accretion disks broadly depend on nuclear fueling modes. Local large-variability and CL Seyferts are in nuclear famine mode, where cold-gas clumps can be formed stochastically in the fueling flow, and their episodic infall produces sharp peaks in the accretion-rate curve. CLQs and EVQs are in feast fueling mode, which may account for both their preference to blue galaxies and their variability pattern (high-amplitude tail of the continuous distribution). Lastly, we propose a new thinking: to search for IMBHs by optical variability in red galaxies.
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