arXiv 0806.28632008-06-17astro-ph

用核星暴遮蔽活动星系核

Obscuring Active Galactic Nuclei with Nuclear Starburst Disks

D. R. Ballantyne

备注：: 13 pages, 12 figures, 3 in color; accepted by ApJ
DOI：: 10.1086/591048

摘要：

我们评估核星爆盘的潜力，以掩盖主导的硬X射线背景在z~1的Seyfert-like活动星系核。超过1200个星爆盘模型，基于汤普森等人开发的理论，计算的五个输入参数：黑洞质量，星爆盘的径向尺寸，尘埃气体比，角动量传输的效率在磁盘，和气体分数在外部磁盘半径。我们发现，一个大的尘埃-气体比，一个相对较小的星爆盘，一个显着的气体质量分数，和有效的角动量传输都是重要的，以产生一个星爆盘，可以潜在地掩盖活动星系核。典型的最大恒星形成速率是每年约10个太阳质量。假设没有由于外流而造成的质量损失，星爆盘以足以产生10^{43}-10 ^<$44}尔格·秒^{-1}的硬X射线光度的速率向黑洞输送气体。星暴盘本身应该可以在中红外线和无线电波段探测到;在z=0.8时，预测的通量在24微米处约为1 mJy，在1.4GHz处约为10-30 microJy。因此，我们预测很大一部分的无线电/X射线匹配在未来的深无线电调查。在赫歇尔未来的100微米巡天中，星暴盘应该很容易与活动星系核区分开来，预计通量约为5 mJy。任何活动星系核遮蔽的星暴都将与热尘埃有关，独立于活动星系核的加热，从而产生可观察到的分离星系和核恒星形成的特征。最后，由于气体和恒星形成之间的竞争，核恒星爆发将与低光度活动星系核相关联。因此，这种现象是一个自然的解释所观察到的减少的部分模糊AGN的光度。

英文摘要：

We assess the potential of nuclear starburst disks to obscure the Seyfert-like AGN that dominate the hard X-ray background at z~1. Over 1200 starburst disk models, based on the theory developed by Thompson et al., are calculated for five input parameters: the black hole mass, the radial size of the starburst disk, the dust-to-gas ratio, the efficiency of angular momentum transport in the disk, and the gas fraction at the outer disk radius. We find that a large dust-to-gas ratio, a relatively small starburst disk, a significant gas mass fraction, and efficient angular momentum transport are all important to produce a starburst disk that can potentially obscure an AGN. The typical maximum star-formation rate in the disks is ~10 solar masses per year. Assuming no mass-loss due to outflows, the starburst disks feed gas onto the black hole at rates sufficient to produce hard X-ray luminosities of 10^{43}-10^{44} erg s^{-1}. The starburst disks themselves should be detectable at mid-infrared and radio wavelengths; at z=0.8, the predicted fluxes are ~1 mJy at 24microns and ~10-30 microJy at 1.4GHz. Thus, we predict a large fraction of radio/X-ray matches in future deep radio surveys. The starburst disks should be easily distinguished from AGN in future 100microns surveys by Herschel with expected fluxes of ~5 mJy. Any AGN-obscuring starbursts will be associated with hot dust, independent of AGN heating, resulting in observable signatures for separating galactic and nuclear star-formation. Finally, because of the competition between gas and star-formation, nuclear starbursts will be associated with lower-luminosity AGN. Thus, this phenomenon is a natural explanation for the observed decrease in the fraction of obscured AGN with luminosity.

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