半人马座A与IRSF/SIRIUS的氢复合近红外谱线作图
Hydrogen recombination near-infrared line mapping of Centaurus A with IRSF/SIRIUS
摘要：
半人马座A（Centaurus A）是最著名的拥有活动星系核（AGN）的星系之一。最近的研究报告探测到了来自星系晕云的Hα发射，这些云位于岑A核的东北和西南方向，这表明活动星系核喷流可能触发了那里的恒星形成。我们用IRSF 1.4-m望远镜对Cen A进行了近红外谱线成像，并对Paβ进行了窄带滤波，发现在东北和西南区域都没有明显的Paβ辐射。东北区Paβ/Hα比值的上限与典型HII区的预期值一致，符合AGN在那里引发恒星形成的假设。另一方面，西南地区Paβ/Hα的上限值明显低于典型HII地区的预期值。西南区Paβ/Hα比值低的一个可能解释是来自Cen A中心的Hα和Paβ光子被晕云中的尘埃颗粒散射。从西南区Paβ/Hα的上限，我们得到了对尘埃粒度分布的限制，发现它与我们银河系星际介质中看到的一致。
英文摘要：
Centaurus A (Cen A) is one of the most famous galaxies hosting an active galactic nucleus (AGN), where the interaction between AGN activities and surrounding interstellar and intergalactic media has been investigated. Recent studies reported detections of the Hα emission from clouds in the galactic halo toward the northeast and southwest of the nucleus of Cen A, suggesting that AGN jets may have triggered star formation there. We performed near-infrared line mapping of Cen A with the IRSF 1.4-m telescope, using the narrow-band filter tuned for Paβ, from which we find that the Paβ emission is not detected significantly from either northeast or southwest regions. The upper limit of the Paβ/Hα ratio in the northeast region is compatible with that expected for a typical HII region, in line with the scenario that AGNs have triggered star formation there. On the other hand, the upper limit of Paβ/Hα in the southwest region is significantly lower than that expected for a typical HII region. A possibility to explain the low Paβ/Hα ratio in the southwest region is the scattering of Hα and Paβ photons from the center of Cen A by dust grains in the halo clouds. From the upper limit of Paβ/Hα in the southwest region, we obtain constraints on the dust size distribution, which is found to be compatible with those seen in the interstellar medium of our Galaxy.
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