CHANDRA REVEALS HEAVY OBSCURATION AND CIRCUMNUCLEAR STAR FORMATION IN SEYFERT 2 GALAXY NGC 4968
CHANDRA REVEALS HEAVY OBSCURATION AND CIRCUMNUCLEAR STAR FORMATION IN SEYFERT 2 GALAXY NGC 4968
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DOI：
10.3847/1538-4357/835/1/91
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发表时间：
2016-12
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通讯作者：
S. LaMassa;T. Yaqoob;N. Levenson;P. Boorman;T. Heckman;P. Gandhi;J. R. Rigby;C. Urry;A. Ptak
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作者：
S. LaMassa;T. Yaqoob;N. Levenson;P. Boorman;T. Heckman;P. Gandhi;J. R. Rigby;C. Urry;A. Ptak
本文给出了NGC 4968（z = 0.00986）Seyfert 2星系的Chandra成像和光谱分析。我们发现在软带（0.5-2 keV），既不符合窄线区，也没有扩展的无线电发射的扩展（101 kpc）的X射线发射。根据光谱模型，它与正在形成的星星有关（大约2.6-4 M yr−1）。在环核尺度（内部约400 pc）的软发射来自热气体，kT约0.7 keV，而最广泛的热发射是较冷的（kT约0.3 keV）。我们改进了之前对该源中极端Fe Kα等效宽度的测量（），这表明中心引擎完全嵌入康普顿厚度的遮蔽层中。使用符合钱德拉光谱的物理模型，我们得到了康普顿厚度的柱密度（NH > 1.25 × 1024 cm−2）和内禀硬X射线光度（2-10 keV）为1.33 -8 × 1042 erg s−1（取决于假设的遮蔽物的几何形状），这比观测到的大了两个数量级。大的Fe Kα EW表明了一种球形覆盖几何结构，这可以用10 keV以上的X射线测量来证实。NGC 4968类似于其他表现出极端Fe Kα EWs的活动星系（即，>2 keV），因为它们也包含正在进行的星星形成。这项工作支持了这样一种观点，即与核星星形成有关的气体可能会增加包围气体的覆盖因子，并在遮蔽活动星系核方面发挥作用。
We present the Chandra imaging and spectral analysis of NGC 4968, a nearby (z = 0.00986) Seyfert 2 galaxy. We discover extended (∼1 kpc) X-ray emission in the soft band (0.5–2 keV) that is neither coincident with the narrow line region nor the extended radio emission. Based on spectral modeling, it is linked to on-going star formation (∼2.6–4 M⊙ yr−1). The soft emission at circumnuclear scales (inner ∼400 pc) originates from hot gas, with kT ∼ 0.7 keV, while the most extended thermal emission is cooler (kT ∼ 0.3 keV). We refine previous measurements of the extreme Fe Kα equivalent width in this source ( ), which suggests the central engine is completely embedded within Compton-thick levels of obscuration. Using physically motivated models fit to the Chandra spectrum, we derive a Compton-thick column density (NH > 1.25 × 1024 cm−2) and an intrinsic hard (2–10 keV) X-ray luminosity of ∼3–8 × 1042 erg s−1 (depending on the presumed geometry of the obscurer), which is over two orders of magnitude larger than that observed. The large Fe Kα EW suggests a spherical covering geometry, which could be confirmed with X-ray measurements above 10 keV. NGC 4968 is similar to other active galaxies that exhibit extreme Fe Kα EWs (i.e., >2 keV) in that they also contain on-going star formation. This work supports the idea that gas associated with nuclear star formation may increase the covering factor of the enshrouding gas and play a role in obscuring active galactic nuclei.