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arXiv 0910.0580astro-ph.COastro-ph.GA
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双峰窄线活动星系核:它们是双重活动星系核吗?

Active Galactic Nuclei with Double-peaked Narrow Lines: Are They Dual AGNs?

J. -M Wang, Y. -M. Chen, C. Hu, W. -M. Mao, S. Zhang, W. -H. Bian

摘要:

双峰[O III]5007,活动星系核(AGN)的剖面可能提供双重AGN存在的证据,但目前缺乏一个很好的诊断选择他们。从SDSS DR 7中的$\sim$ 7000个活动星系出发,我们收集了87个具有双峰[O III]5007型活动星系核的样本。2型活动星系核的核遮蔽使我们能够通过恒星吸收线来确定宿主星系的红移。我们通常会发现,相对于宿主星系,一个峰红移,另一个峰蓝移。我们发现的位移和双峰通量的比率之间有很强的相关性。这种相关性可以很自然地用同向旋转对偶活动星系核模型所预言的开普勒关系来解释。目前的样本统计上支持大多数[O III]双峰源是双重活动星系核,而不支持其他解释,如旋转盘和外流。这些对偶活动星系核的分离距离为$\sim 1$ kpc尺度,显示了合并系统的中间阶段。对偶活动星系核的出现大约是$\sim 10^{-2}$,以$\sim 10^{-4}$的概率影响了目前对双星超大质量黑洞的观测不足(Boroson & Lauer)。

英文摘要:

Double-peaked [O III]5007, profiles in active galactic nuclei (AGNs) may provide evidence for the existence of dual AGNs, but a good diagnostic for selecting them is currently lacking. Starting from $\sim$ 7000 active galaxies in SDSS DR7, we assemble a sample of 87 type 2 AGNs with double-peaked [O III]5007, profiles. The nuclear obscuration in the type 2 AGNs allows us to determine redshifts of host galaxies through stellar absorption lines. We typically find that one peak is redshifted and another is blueshifted relative to the host galaxy. We find a strong correlation between the ratios of the shifts and the double peak fluxes. The correlation can be naturally explained by the Keplerian relation predicted by models of co-rotating dual AGNs. The current sample statistically favors that most of the [O III] double-peaked sources are dual AGNs and disfavors other explanations, such as rotating disk and outflows. These dual AGNs have a separation distance at $\sim 1$ kpc scale, showing an intermediate phase of merging systems. The appearance of dual AGNs is about $\sim 10^{-2}$, impacting on the current observational deficit of binary supermassive black holes with a probability of $\sim 10^{-4}$ (Boroson & Lauer).

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