Radio structures of the nuclei of nearby Seyfert galaxies and the nature of the missing diffuse emission
Radio structures of the nuclei of nearby Seyfert galaxies and the nature of the missing diffuse emission
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DOI：
10.1111/j.1365-2966.2009.15837.x
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发表时间：
2009-11
影响因子：
4.8
通讯作者：
M. Orienti;M. Prieto;Iac;Inaf-Ira;Bologna
中科院分区：
文献类型：
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作者：
M. Orienti;M. Prieto;Iac;Inaf-Ira;Bologna
我们提供南半球最近、最亮的七个塞弗特星系核的高分辨率空间分辨率 VLA 和 VLBA 档案数据。在 VLA 分辨率（~0.1 角秒）下，Seyfert 星系的核尚未解析，但 MCG-5-23-16 和 NGC 7469 除外，它们显示出核心喷流结构。三个赛弗特核被与恒星形成区域相关的漫射无线电发射包围。具有秒差距尺度分辨率的 VLBA 观测表明，在 MRK 1239 中，原子核清楚地分解为相距约 30 pc 的两个部分，而 NGC 3783 的原子核则未分解。进一步比较这两个源的VLA和VLBA数据表明，秒差距尺度的通量密度仅为VLA测量的20%。这表明射电发射并不像椭圆形射电星系那样集中在单个中心组件中，并且必须存在额外的低表面亮度组件。赛弗特核与不同无线电频谱的比较表明，在陡频谱物体中，毫弧秒尺度上未检测到的通量的“存在”很常见，而在平频谱物体中，基本上所有无线电发射都被恢复。在陡峭光谱天体中，这种“缺失”的通量可能是由与活动星系核相关的非热辐射造成的，也可能是由于塞弗特星系中螺旋宿主环境更密集而被破坏的喷流造成的。
We present archival high-spatial-resolution VLA and VLBA data of the nuclei of seven of the nearest and brightest Seyfert galaxies in the Southern Hemisphere. At VLA resolution (∼0.1 arcsec), the nuclei of the Seyfert galaxies are unresolved, with the exception of MCG-5-23-16 and NGC 7469, which show a core-jet structure. Three Seyfert nuclei are surrounded by diffuse radio emission related to star-forming regions. VLBA observations with parsec-scale resolution demonstrate that in MRK 1239 the nucleus is clearly resolved into two components separated by ∼30 pc, whereas the nucleus of NGC 3783 is unresolved. Further comparison between VLA and VLBA data of these two sources shows that the flux density at parsec scales is only 20 per cent of that measured by the VLA. This suggests that the radio emission is not concentrated in a single central component, as in elliptical radio galaxies, and an additional low-surface-brightness component must be present. A comparison of Seyfert nuclei with different radio spectra shows that the 'presence' of undetected flux on a milliarcsecond scale is common in steep-spectrum objects, whereas in flat-spectrum objects essentially all the radio emission is recovered. In the steep-spectrum objects, this 'missing' flux probably results from non-thermal radiation related to active galactic nuclei , perhaps from a jet that is disrupted in Seyfert galaxies because of the denser environment of their spiral hosts.