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arXiv 0910.3771astro-ph.COastro-ph.GA
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最近的AGN中心秒差距的谱能量分布

The spectral energy distribution of the central parsecs of the nearest AGN

M. A. Prieto, J. Reunanen, K. R. W. Tristram, N. Neumayer, J. A. Fernandez-Ontiveros, M. Orienti, K. Meisenheimer

摘要:

本文给出了一些最近的、研究得最好的活动星系核(AGN)中心几十秒差距区域的光谱能量分布(SED)。这些真正的活动星系核SEDs,主要来自塞弗特星系,其特征在于两个主要特征:一个最大值在2-10微米范围内的红外凸起,以及在1至~200 keV区域内增加的X射线光谱。这些主要特征是共同的塞弗特1型和2型物体一样。2型活动星系核表现出2微米的急剧下降,光学到UV区域被完全吸收,而1型活动星系核则表现出2微米的轻微下降,随后是次级的、部分吸收的光学到UV发射凸起。假设在这些活动星系核中产生的大部分光学到紫外光子被尘埃再处理,并以各向同性的方式在红外线中重新发射,红外线凸块亮度占这些物体总能量输出的70%以上,而20 keV以上的高能量是第二大能量贡献。星系核通常被归类为活动星系核,因为它们的暖红外颜色,即在12至60微米范围内呈现相对平坦的通量分布。这些高空间分辨率SED的结果质疑这一标准作为一个一般规则。研究发现,活动星系核的红外辐射能量的固有形状和由此推断的辐射光度与大口径观测结果有很大的偏差。活动星系核的光度,如果依赖于红外卫星数据,可以高估两个数量级。我们发现,这些差异是关键的AGN光度低于或约10^{44}尔格/秒。超过这个极限,活动星系核倾向于支配其宿主星系的光,而不管使用的孔径大小。我们尝试性地将这个光度标记为识别星系光与活动星系核主导天体的阈值。

英文摘要:

Spectral energy distributions (SEDs) of the central few tens of parsec region of some of the nearest, most well studied, active galactic nuclei (AGN) are presented. These genuine AGN-core SEDs, mostly from Seyfert galaxies, are characterised by two main features: an IR bump with the maximum in the 2-10 micron range, and an increasing X-ray spectrum in the 1 to ~200 keV region. These dominant features are common to Seyfert type 1 and 2 objects alike. Type 2 AGN exhibit a sharp drop shortward of 2 micron, with the optical to UV region being fully absorbed, while type 1s show instead a gentle 2 micron drop ensued by a secondary, partially-absorbed optical to UV emission bump. Assuming the bulk of optical to UV photons generated in these AGN are reprocessed by dust and re-emitted in the IR in an isotropic manner, the IR bump luminosity represents >70% of the total energy output in these objects while the high energies above 20 keV are the second energetically important contribution. Galaxies selected by their warm IR colours, i.e. presenting a relatively-flat flux distribution in the 12 to 60 micron range have often being classified as AGN. The results from these high spatial resolution SEDs question this criterion as a general rule. It is found that the intrinsic shape of the IR SED of an AGN and inferred bolometric luminosity largely depart from those derived from large aperture data. AGN luminosities can be overestimated by up to two orders of magnitude if relying on IR satellite data. We find these differences to be critical for AGN luminosities below or about 10^{44} erg/s. Above this limit, AGNs tend to dominate the light of their host galaxy regardless of the aperture size used. We tentatively mark this luminosity as a threshold to identify galaxy-light- vs AGN- dominated objects.

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