Adaptive Optics Imaging and Spectroscopy of Cygnus A. I. Evidence for a Minor Merger
Adaptive Optics Imaging and Spectroscopy of Cygnus A. I. Evidence for a Minor Merger
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Cygnus A.I. 的自适应光学成像和光谱学小型合并的证据
DOI：
10.1086/378513
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发表时间：
2003
期刊：
影响因子：
--
通讯作者：
S. Dahm
中科院分区：
文献类型：
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作者：
G. Canalizo;C. Max;D. Whysong;R. Antonucci;S. Dahm
我们展示了 Keck II 自适应光学近红外成像和对强大射电星系 Cyg A 中心区域的光谱观测。0.”05 分辨率图像清楚地显示了两个壮观的电离/散射锥之间未解析的核。我们报告在射电核西南投影中发现了一个相对明亮（K′~19）的次级点源0.″4或400 pc。该物体在哈勃太空望远镜档案光学图像中也可见，尽管它很容易与宿主的底层结构混淆。尽管这个次要点源的近红外颜色与 L 矮星的近红外颜色大致一致，但其光谱和光学到红外光谱能量分布 (SED) 实际上排除了它可能是任何前景投影物体的可能性。我们得出的结论是，次要点源很可能是与 Cyg A 相关的河外天体。我们考虑了对该天体性质的几种解释，包括：一个年轻的星团透过电离锥边缘的尘埃凝视；一个较古老的大型球状星团；致密的尘埃或电子云，充当隐藏的活性核的镜子；以及正在与巨大椭圆星系合并的气体剥离卫星星系的致密核心。这里提供的数据与小型合并场景最为一致。该物体的光谱和SED表明，它可能是一个被尘埃严重灭绝的老恒星的密集聚集体，其高光度和致密性质与被剥离至潮汐半径的卫星的特征一致。然而，需要进一步的光谱观察来证实这种可能性。
We present Keck II adaptive optics near-infrared imaging and spectroscopic observations of the central regions of the powerful radio galaxy Cyg A. The 0.″05 resolution images clearly show an unresolved nucleus between two spectacular ionization/scattering cones. We report the discovery of a relatively bright (K′ ~ 19) secondary point source 0.″4 or 400 pc in projection southwest of the radio nucleus. The object is also visible in archival Hubble Space Telescope optical images, although it is easily confused with the underlying structure of the host. Although the near-infrared colors of this secondary point source are roughly consistent with those of an L dwarf, its spectrum and optical-to-infrared spectral energy distribution (SED) virtually rule out the possibility that it may be any foreground projected object. We conclude that the secondary point source is likely to be an extragalactic object associated with Cyg A. We consider several interpretations of the nature of this object, including: a young star cluster peering through the dust at the edge of one of the ionization cones; an older, large globular cluster; a compact cloud of dust or electrons that is acting as a mirror of the hidden active nucleus; and the dense core of a gas-stripped satellite galaxy that is merging with the giant elliptical host. The data presented here are most consistent with the minor merger scenario. The spectra and SED of the object suggest that it may be a densely packed conglomeration of older stars heavily extincted by dust, and its high luminosity and compact nature are consistent with those of a satellite that has been stripped to its tidal radius. Further spectroscopic observations are nevertheless necessary to confirm this possibility.