NGC 90：隐藏的水母星系？
NGC 90: a hidden jelly-fish galaxy?
摘要：
利用俄罗斯6米望远镜BTA的长狭缝光谱观测和SDSS测光资料，研究了相互作用系统Arp 65（NGC 90/93）的一对成员星系NGC 90。这个星系展示了两个包含年轻恒星星族的潮汐尾，是其“宏伟设计”螺旋臂的延伸。得到了两种狭缝取向下的速度分布和氧丰度分布。在星系的中心部分，一个重要的作用属于非光电离机制的线发射可能造成的冲击，由于LINER类活动的核。O/H有一个浅的丰度梯度，典型的相互作用的星系。该星系最令人感兴趣的特点是存在较早发现的巨大HI“云”，其中含有约一半的星系气体总质量，它强烈地向外位移，速度超过主星系的中心速度约340公里/秒。我们在“云”中发现了当前恒星形成的痕迹，尽管云显然与星系没有引力约束。讨论了“云”的可能性质。我们认为，它提出了一个气体流动的冲压压力席卷和延长沿视线。
英文摘要：
We study a peculiar galaxy NGC 90, a pair member of interacting system Arp 65 (NGC 90/93), using the long-slit spectral observations carried out at the Russian 6m telescope BTA and the available SDSS photometric data. This galaxy demonstrates two tidal tails containing young stellar population, being an extension of its `Grand Design' spiral arms. We obtained the distribution of velocity and oxygen abundance of emission gas (O/H) for two slit orientations. In the central part of the galaxy a significant role belongs to non-photoionization mechanism of line emission probably caused by shocks due to LINER-like activity of the nucleus. The O/H has a shallow abundance gradient, typical for interacting galaxies. The most intriguing peculiarity of the galaxy is the presence of the discovered earlier huge HI `cloud' containing about half of total mass of galaxy gas, which is strongly displaced outwards and has a velocity exceeding at about 340 km/s the central velocity of the main galaxy. We found traces of current star formation in the `cloud', even though the cloud is apparently not gravitationally bound with the galaxy. A possible nature of the `cloud' is discussed. We argue that it presents a flow of gas sweeping by ram pressure and elongated along a line of sight.
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