NGC253的恒星运动学中心和真星系核
The Stellar Kinematic Center and the True Galactic Nucleus of NGC253
摘要：
我们提出了第一个亚弧秒分辨率的二维恒星运动学和X射线观测的原型星暴星系NGC 253定义的星系核的位置和性质。我们得到了恒星运动学中心位置的估计，对应于一个区域的r~1.2”中心0.7”西南从无线电核心（TH 2）。新处理的钱德拉数据揭示了一个中央硬X射线源（X-1）位于运动中心西南0.4”处。无线电、红外线和X射线源之间非常精确的对准表明，TH 2、红外光度中心和X-1彼此之间没有关联。由于运动学中心与TH 2和X-1一致，我们认为这两个可能的星系核候选者。虽然TH 2是核区域中最强的射电源，但它没有任何红外，光学或X射线对应物。如果运动中心与这个源有关，通过类比，我们认为NGC 253的核类似于我们的银河系中心SgrA*。另一方面，X-1是一个严重吸收的物体，只能在能量>2 keV时探测到。如果X-1与运动中心相关，那么NGC 253的核心与一个被遮蔽的低光度活动星系核（AGN）或一个空间分辨的超级星团（SSC）相一致，它们在X射线中变亮，很可能是由于年轻的超新星或超新星遗迹。如果没有SSC与运动学中心相关联，我们可以得出结论，NGC 253是一个强星暴和弱活动星系核（TH 2或X-1）共存的星系。其他一些高分辨率的研究结果表明，在这些系统中的活动星系核，如果存在的话，总是在低光度制度。这可能表明星系核活动的开始与恒星形成的发生密切相关，我们正在目睹活动星系核的出现或消失。
英文摘要：
We present the first sub-arcsecond resolution two-dimensional stellar kinematics and X-ray observations of the prototypical starburst galaxy NGC253 which define the position and nature of the galactic nucleus. We get an estimate of the stellar kinematic center location corresponding to an area of r~1.2" centered 0.7" southwest from the radio core (TH2). Newly processed Chandra data reveal a central hard X-ray source (X-1) lying 0.4" southwest from the kinematic center. Very accurate alignment between radio, infrared and X-ray sources shows that TH2, the IR photometric center and X-1 are not associated with each other. As the kinematic center is consistent with TH2 and X-1, we consider the two as possible galactic nucleus candidates. Although TH2 is the strongest radio source in the nuclear region, it does not have any infrared, optical or X-ray counterparts. If the kinematic center is associated with this source, by analogy we suggest that the nucleus of NGC253 resembles our Galactic Center SgrA*. On the other hand, X-1 is a heavily absorbed object only detected at energies >2 keV. If X-1 is instead associated with the kinematic center, the nucleus of NGC253 is compatible with an obscured low luminosity active galactic nucleus (AGN) or a spatially resolved super star cluster (SSC) brightening up in X-rays most probably due to young supernovae or supernova remnants. If no SSC is associated with the kinematic center, we conclude that NGC253 is a galaxy in which a strong starburst and a weak AGN (either TH2 or X-1) coexist. Results from few other high resolution studies of nearby starburst galaxies indicate that the AGN in these systems, if present, is always in the low luminosity regime. This may indicate that the onset of nuclear activity in galaxies is closely related with the occurrence of star formation, and that we are witnessing the emergence or disappearance of an AGN.
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