标题： 对边缘星系的CO观测，V. NGC 5907中的气体中心缺失—— 核球中的合并 显示英文标题

标题： CO Observations of Edge-on Galaxies, V. NGC 5907: Central Deficiency of Gas in an Sc Galaxy - Merger in the Bulge

摘要： 旋涡星系NGC 5907的边缘观测是在12CO(1-0)线发射中使用了 Nobeyama 45 米望远镜。 在2到13千秒差距之间的径向密度分布可以用一个尺度半径为3.5千秒差距的指数律盘和一个7千秒差距半径的环的叠加来很好地表示。 然而，在其中心2千秒差距内没有观测到气体的聚集。 径向分布和位置-速度图与HI获得的结果进行了详细的比较。 我们发现，在其中心5千秒差距区域内分子气体占主导地位，而外部区域则由HI主导，两者被一个“分子前缘”在5千秒差距半径处清晰地分隔开。 这个分子前缘将是银河尺度上从HI到分子氢，或者反之亦然相变发生的地方。 分子气体在中心的缺乏对于一个晚型星系来说是异常的，这是首次在Sc星系中发现的，也是继Sb星系M31之后的第二个案例。 我们认为核区气体盘可能因另一个星系的合并而被破坏，并讨论了它与外部弯曲盘的关系。 显示英文摘要

摘要： The edge-on Sc galaxy NGC 5907 has been observed in the 12CO(1-0)-line emission using the Nobeyama 45-m telescope. The radial density distribution between 2 and 13 kpc is well represented by a superposition of an exponential-law disk of scale radius 3.5 kpc and a ring of 7 kpc radius. However, no concentration of gas has been observed in the central 2 kpc. The radial distribution and position-velocity diagram are compared in detail with those obtained for HI. We found that the molecular gas dominates in the central 5 kpc region, while HI does in the outer region, clearly separated by a ``molecular front'' at 5 kpc radius. This molecular front will be the place where the phase change from HI to molecular hydrogen, or vice versa, is taking place in a galactic scale. The central deficiency of the molecular gas is exceptional for a late type galaxy, which was found for the first time among Sc galaxies, and the second case after the Sb galaxy M31. We argue for the possibility of destruction of the nuclear gas disk by a merger of another galaxy, and discuss its relation to the outer warping disk.