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arXiv 1303.7112astro-ph.CO
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关于红色的性质,2 MASS在本地宇宙I中选择了AGN:光谱研究

On the nature of the red, 2MASS selected AGN in the local Universe I: an optical spectroscopic study

Marvin Rose, Clive Tadhunter, Joanna Holt, Javier Rodríguez Zaurín

摘要:

我们给出了一个具有代表性的27个附近(z < 0.2)2 MASS选择的活动星系核的光谱,这些活动星系核具有红色的近红外颜色(J-K 2.0)。这些光谱是用WHT上的ISIS摄谱仪拍摄的,目的是确定红色2 MASS活动星系核的性质,特别是它们是否是被气体和尘埃的出生茧所掩盖的年轻类星体。我们比较我们的研究结果与PG类星体和未遮蔽的1型活动星系核的比较样本。光谱显示出显著的多样性,包括适度变红的1型天体(45%),与传统的紫外/光学选择活动星系核相似的1型天体(11%),窄线Seyfert 1活动星系核(15%),2型活动星系核(22%)和HII/复合天体(7%)。我们在许多1型天体中测量到的高巴耳末衰减与它们的红色J-KS颜色一致,这是由于中等程度的尘埃消光(0.2 < E(B-V)< 1.2)。然而,我们仅测量了与比较样品中测量的类似的较宽[OIII]λ5007发射线分量的适度速度偏移和宽度。这表明,在红色的2 MASS对象的外流是不寻常的光学/紫外选择AGN类似的光度相比。此外,2 MASS样品的爱丁顿比相对适中。总的来说,基于它们的光谱,我们没有发现明确的证据表明,在低红移的红色,2 MASS选择AGN的人口代表年轻的类星体。最有可能的是,这些物体是正常的1型活动星系核,被环核环面外层或宿主星系盘中的物质适度遮蔽。

英文摘要:

We present optical spectra for a representative sample of 27 nearby (z < 0.2) 2MASS-selected AGN with red near-IR colours (J-K 2.0). The spectra were taken with the ISIS spectrograph on the WHT with the aim of determining the nature of the red 2MASS AGN, in particular whether they are young quasars obscured by their natal cocoon of gas and dust. We compare our findings with those obtained for comparison samples of PG quasars and unobscured type 1 AGN. The spectra show a remarkable variety, including moderately reddened type 1 objects (45%), type 1 objects that appear similar to traditional UV/optical selected AGN (11%), narrow-line Seyfert 1 AGN (15%), type 2 AGN (22%) and HII/composite objects (7%). The high Balmer decrements that we measure in many of the type 1 objects are consistent with their red J-KS colours being due to moderate levels of dust extinction (0.2 < E(B-V) < 1.2). However, we measure only modest velocity shifts and widths for the broader [OIII]λ5007 emission line components that are similar to those measured in the comparison samples. This suggests that the outflows in the red 2MASS objects are not unusual compared with those of optical/UV selected AGN of similar luminosity. In addition, the Eddington ratios for the 2MASS sample are relatively modest. Overall, based on their optical spectra, we find no clear evidence that the population of red, 2MASS selected AGN at low redshifts represents young quasars. Most plausibly, these objects are normal type 1 AGN that are moderately obscured by material in the outer layers of the circum-nuclear tori or in the disks of the host galaxies.

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