在银河系附近对活动星系核进行全面普查：大量光学上无法识别的活动星系核
Towards a Complete Census of AGNs in Nearby Galaxies: A Large Population of Optically Unidentified AGNs
摘要：
利用Spitzer-IRS光谱技术，我们研究了在一个完整的（约94%）体积有限的最亮的测辐射热星系（L_IR >（0.3-20）x 10^10 L_sun）（D < 15 Mpc）样本中活动星系核（AGN）的普遍性。我们的分析是基于高激发发射线[NeV]（λ14.32 μ m; 97.1 eV）的检测，以明确地确定活动星系核的活动。我们发现在我们的样本中的64个红外亮星系中有17个星系有活动星系核活动（~27^{+8}_{-6}%），其中超过50%的星系不能被光谱学识别为活动星系核。大的活动星系核分数表明，活动星系核活动和红外光度之间的联系更紧密的星系在本地宇宙比以前发现的，可能表明活动星系核活动和恒星形成之间的密切联系。这些光学上未被确认的活动星系核跨越了广泛的星系类型（S 0-Ir），并且通常是以恒星爆发为主的系统，具有中等亮度的活动星系核活动（L_[NeV] ~ 10^37 - 10^39 erg s^-1）。在大多数这些星系的光学活动星系核签名的非识别似乎是由于对活动星系核的消光，而不是本质上的低光度活动星系核活动。光学图像的检查表明，光学身份不明的活动星系核与灭绝的证据是托管在高度倾斜的星系或星系的尘埃带，表明活动星系核的模糊不一定是由于一个模糊的环面。因此，我们的结论是，光学光谱调查错过了大约一半的活动星系核人口仅仅是由于通过宿主星系的灭绝。
英文摘要：
Using Spitzer-IRS spectroscopy, we investigate the ubiquity of Active Galactic Nuclei (AGN) in a complete (~94%), volume-limited sample of the most bolometrically-luminous galaxies (L_IR > (0.3-20) x 10^10 L_sun) to D < 15 Mpc. Our analyses are based on the detection of the high-excitation emission line [NeV](λ14.32 um; 97.1 eV) to unambiguously identify AGN activity. We find that 17 of the 64 IR-bright galaxies in our sample host AGN activity (~27^{+8}_{-6}%), >50% of which are not identified as AGNs using optical spectroscopy. The large AGN fraction indicates a tighter connection between AGN activity and IR luminosity for galaxies in the local Universe than previously found, potentially indicating a close association between AGN activity and star formation. The optically unidentified AGNs span a wide range of galaxy type (S0-Ir) and are typically starburst-dominated systems hosting modest-luminosity AGN activity (L_[NeV] ~ 10^37 - 10^39 erg s^-1). The non-identification of optical AGN signatures in the majority of these galaxies appears to be due to extinction towards the AGN, rather than intrinsically low-luminosity AGN activity. Examination of optical images shows that the optically unidentified AGNs with evidence for extinction are hosted in either highly inclined galaxies or galaxies with dust lanes, indicating that obscuration of the AGN is not necessarily due to an obscuring torus. We therefore conclude that optical spectroscopic surveys miss approximately half of the AGN population simply due to extinction through the host galaxy.
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