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arXiv 0908.2426astro-ph.CO
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具有双峰[O III ]线的2型活动星系核:窄线区动力学还是合并超大质量黑洞对?

Type 2 AGNs with Double-Peaked [O III] Lines: Narrow Line Region Kinematics or Merging Supermassive Black Hole Pairs?

Xin Liu, Yue Shen, Michael A. Strauss, Jenny E. Greene

摘要:

我们从斯隆数字巡天第七次数据中选取了167个具有双峰[O III] 4959,5007窄发射线的2型活动星系核样本。双峰分布可以很好地模拟两个速度分量,蓝移和红移的系统速度。这些天体中有一半有更突出的红移分量。在H-beta发射线很强的情况下,它还显示了两个速度分量,其视线(LOS)速度偏移与[O III]一致。两个分量之间的相对LOS速度偏移通常为几百km/s,比每个分量的半峰线全宽大约1.5倍。偏移量与宿主恒星速度色散σ * 相关。这个样本的宿主星系系统地显示出更大的sigma*、恒星质量和浓度,以及比在红移、[O III] 5007等效宽度和光度上匹配的常规2型活动星系核样本更老的光度加权平均恒星年龄;它们在射电性质上没有显着差异。这些双峰特征可能是由于窄线区域运动学,或二元黑洞。统计特性并没有显示出强烈的偏好或反对任何一种情况下,空间分辨光学成像,光谱,无线电或X射线后续需要得出明确的结论。

英文摘要:

We present a sample of 167 type 2 AGNs with double-peaked [O III] 4959,5007 narrow emission lines, selected from the Seventh Data Release of the Sloan Digital Sky Survey. The double-peaked profiles can be well modeled by two velocity components, blueshifted and redshifted from the systemic velocity. Half of these objects have a more prominent redshifted component. In cases where the H-beta emission line is strong, it also shows two velocity components whose line-of-sight (LOS) velocity offsets are consistent with those of [O III]. The relative LOS velocity offset between the two components is typically a few hundred km/s, larger by a factor of ~ 1.5 than the line full width at half maximum of each component. The offset correlates with the host stellar velocity dispersion sigma*. The host galaxies of this sample show systematically larger sigma*, stellar masses, and concentrations, and older luminosity-weighted mean stellar ages than a regular type 2 AGN sample matched in redshift, [O III] 5007 equivalent width and luminosity; they show no significant difference in radio properties. These double-peaked features could be due to narrow-line region kinematics, or binary black holes. The statistical properties do not show strong preference for or against either scenario, and spatially resolved optical imaging, spectroscopy, radio or X-ray followup are needed to draw firm conclusions.

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