Near-infrared K-Band Spectroscopic Investigation of Seyfert 2 Nuclei in the CfA and 12 Micron Samples
Near-infrared K-Band Spectroscopic Investigation of Seyfert 2 Nuclei in the CfA and 12 Micron Samples
复制标题
DOI：
10.1086/423424
复制
发表时间：
2004-07
期刊：
影响因子：
--
通讯作者：
M. Imanishi;A. Alonso-Herrero
中科院分区：
文献类型：
--
作者：
M. Imanishi;A. Alonso-Herrero
我们给出了25个塞弗特2星系核和12个μm样品的近红外K带狭缝光谱。由恒星产生的2.3-2.4μm的CO吸收特征的强度是用光谱CO指数来测量的。观测到的CO指数与核K-L色之间存在明显的反相关关系，这表明由活动星系核加热的无特征的热尘埃连续体对观测到的塞弗特2星系核中的K带通量有重要贡献。在对活动星系核的这一贡献进行校正后，我们估计了所有源的核恒星K带光度，并估计了观测到的CO指数相对较大的源的CO指数。10个(=40%)Seyfert 2核的修正CO指数与恒星形成星系或椭圆形星系中观测到的CO指数一样高。结合K波段数据和L波段3.3μm多环芳烃发射特征的测量，发现3.3μm多环芳烃与K波段恒星光度比明显小于星暴星系。我们的结果表明，3.3μm多环芳烃辐射起源于围绕活动星系核周围尘埃环带的核星暴，因为它的表面亮度很高，而在核内探测到的K波段CO吸收特征主要是由老的球状恒星构成的，因此可能不是核星暴的有力指示。我们在12μm Seyfert2星系和CFA星系之间的CO吸收和多环芳烃发射特征的强度上没有明显的区别。
We present near-infrared K-band slit spectra of the nuclei of 25 Seyfert 2 galaxies in the CfA and 12 μm samples. The strength of the CO absorption features at 2.3-2.4 μm produced by stars is measured in terms of a spectroscopic CO index. A clear anticorrelation between the observed CO index and the nuclear K - L color is present, suggesting that a featureless hot dust continuum heated by an active galactic nucleus (AGN) contributes significantly to the observed K-band fluxes in the nuclei of Seyfert 2 galaxies. After correction for this AGN contribution, we estimate nuclear stellar K-band luminosities for all sources and CO indices for sources with modestly large observed CO indices. The corrected CO indices for 10 (=40%) Seyfert 2 nuclei are found to be as high as those observed in star-forming or elliptical (=spheroidal) galaxies. We combine the K-band data with measurements of the L-band 3.3 μm polycyclic aromatic hydrocarbon (PAH) emission feature, another powerful indicator for star formation, and find that the 3.3 μm PAH to K-band stellar luminosity ratios are substantially smaller than those of starburst galaxies. Our results suggest that the 3.3 μm PAH emission originates in the putative nuclear starbursts in the dusty tori surrounding the AGNs, because of its high surface brightness, whereas the K-band CO absorption features detected at the nuclei are dominated by old bulge (=spheroid) stars and thus may not be a powerful indicator for the nuclear starbursts. We see no clear difference in the strength of the CO absorption and PAH emission features between the CfA and 12 μm Seyfert 2 galaxies.