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arXiv 0907.4144astro-ph.CO
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探测Seyfert星系的近红外恒星星族

Probing the near infrared stellar population of Seyfert galaxies

R. Riffel, M. G. Pastoriza, A. Rodriguez-Ardila, C. Bonatto

摘要:

利用IRTF SpeX近红外光谱(0.8-2.4 μ m)研究了9个Sy 1和15个Sy 2星系的恒星星族(SP)、活动星系核(AGN)、无特征连续体(FC)和热尘埃的性质。星光代码和热尘埃作为额外的基本元素都是第一次在这个光谱范围内使用。我们发现了等效宽度(W)Si I 1.59微米x Mg I 1.58微米之间相关性的证据,这两种活性相同。部分W{Na I 2.21微米}和W {CO 2.3微米}强度可能与星系倾角有关。我们的综合结果显示了Sy 1和Sy 2星系之间的显著差异:约90%的Sy 1星系需要热尘成分来拟合K波段光谱,而Sy 2星系只有约25%需要热尘成分,约50%的Sy 2星系需要$FC$成分的贡献> 20%,而Sy 1中这一比例增加到60%;此外,在Sy 2的50%中,FC和年轻成分的组合贡献超过20%,而在Sy 1的90%中,这表明中心区域最近有恒星形成。我们星系样本的中央几百秒差距包含相当大一部分的中间年龄SP,其平均金属丰度接近太阳。我们的SP合成证实,1.1微米CN带可用作中间年龄SP的示踪剂。SP,FC和热尘埃成分的同时拟合增加了约150%的活动星系核的数量与热尘埃检测和质量估计。与通常严重衰减的光学范围相反,近红外光谱是研究Sy 1星系恒星星族的一个很好的窗口。我们的方法开辟了一个新的途径来调查和量化的三个最重要的近红外连续分量观测活动星系核的个人贡献。

英文摘要:

We employ IRTF SpeX NIR (0.8-2.4 microns) spectra to investigate the stellar population (SP), active galactic nuclei (AGN) featureless continuum (FC) and hot dust properties in 9 Sy 1 and 15 Sy 2 galaxies. Both the starlight code and the hot dust as an additional base element were used for the first time in this spectral range. We found evidence of correlation among the equivalent widths (W) Si I 1.59 microns x Mg I 1.58 microns, equally for both kinds of activity. Part of the W{Na I 2.21 microns} and W {CO 2.3 microns} strengths may be related to galaxy inclination. Our synthesis shows significant differences between Sy 1 and Sy 2 galaxies: the hot dust component is required to fit the K-band spectra of ~90% of the Sy 1 galaxies, and only of ~25% of the Sy 2; about 50 % of the Sy 2 galaxies require a $FC$ component contribution >20%, while this fraction increases to 60% in the Sy 1; also, in about 50 % of the Sy2, the combined FC and young components contribute with more than 20%, while this occurs in 90% of the Sy1, suggesting recent star formation in the central region. The central few hundred parsecs of our galaxy sample contain a substantial fraction of intermediate-age SPs with a mean metallicity near solar. Our SP synthesis confirms that the 1.1 micron CN band can be used as a tracer of intermediate-age SPs. The simultaneous fitting of SP, FC and hot dust components increased in ~150% the number of AGNs with hot dust detected and the mass estimated. The NIR emerges as an excellent window to study the stellar population of Sy 1 galaxies, as opposed to the usually heavily attenuated optical range. Our approach opens a new way to investigate and quantify the individual contribution of the three most important NIR continuum components observed in AGNs.

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