CHANG-ES VIII：揭示射电极化中隐藏的AGN活动
CHANG-ES VIII: Uncovering Hidden AGN Activity in Radio Polarization
摘要：
本文报道了对NGC 2992星系的C波段（5 - 7 GHz）观测结果。这个星系在其螺旋盘中显示出嵌入的核双叶射电形态，如线偏振发射所揭示的，但在总强度发射中{ \it not}。射电瓣大小为千帕秒差距，与过去观测到的其他塞弗特星系相似，并显示出有序的磁场。NGC~2992以前曾显示过活动星系核相关活动的证据，但没有我们在这里提出的线性极化射电特征。我们提请注意这个星系作为第一个明确的例子（和原型）的双极无线电流出，揭示了线偏振发射。这样的偏振观测，这是未被尘埃掩盖，提供了一个新的工具，揭示隐藏的弱活动星系核活动，否则可能被掩盖的更明亮的非偏振的发射，它是嵌入。在NGC~2992中观测到的射电瓣与周围的星际介质相互作用，为研究核外流与邻近星系ISM之间的相互作用提供了新的机会。我们还比较了无线电发射与一个新的CHANNEL X射线图像的这个星系。最后还简要地给出了NGC~3079的一张新的CHANG-ES图像，作为另一个例子，说明了相对于总强度而言，线偏振的射电瓣出现得更为明显。
英文摘要：
We report on C-band (5 - 7 GHz) observations of the galaxy, NGC~2992, from the CHANG-ES sample. This galaxy displays an embedded nuclear double-lobed radio morphology within its spiral disk, as revealed in linearly polarized emission but {\it not} in total intensity emission. The radio lobes are kpc-sized, similar to what has been observed in the past for other Seyfert galaxies, and show ordered magnetic fields. NGC~2992 has shown previous evidence for AGN-related activity, but not the linearly polarized radio features that we present here. We draw attention to this galaxy as the first clear example (and prototype) of bipolar radio outflow that is revealed in linearly polarized emission only. Such polarization observations, which are unobscured by dust, provide a new tool for uncovering hidden weak AGN activity which may otherwise be masked by brighter unpolarized emission within which it is embedded. The radio lobes observed in NGC~2992 are interacting with the surrounding interstellar medium and offer new opportunities to investigate the interactions between nuclear outflows and the ISM in nearby galaxies. We also compare the radio emission with a new CHANDRA X-ray image of this galaxy. A new CHANG-ES image of NGC~3079 is also briefly shown as another example as to how much more obvious radio lobes appear in linear polarization as opposed to total intensity.
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