标题： 近红外和光学形态的尘埃星系 NGC972 显示英文标题

标题： Near infrared and optical morphology of the dusty galaxy NGC972

摘要： 近红外（NIR）和光学表面光度分析结果展示了尘埃星系NGC972。 BVRJHK波段的光度轮廓可以用高斯轮廓和指数轮廓的组合进行拟合，分别对应于恒星爆发核心和恒星盘。 B波段的指数尺度长度是K波段的2.8倍，这意味着中心B波段的光学深度高达11。 即使在近红外波段也不存在隆起，因此该星系的形态类型必须比通常采用的Sb型更晚。 相对较低的旋转速度和较高的气体含量也支持该星系为较晚的类型，可能是Sd型。 在老年恒星的分布中只能追踪到一条臂；然而，在尘埃和HII区域的分布中可以追踪到第二条臂。 数据表明存在一个短的NIR棒，其结束于核环内部。 旋转曲线缓慢上升的特性排除了核环的共振起源。 考虑到星系具有中等倾斜度但环呈现圆形外观，该环很可能不在星系平面内。 恒星形成环的非平面性质、总质量中以分子形式存在的异常高比例（30%）、核恒星爆发的存在以及螺旋臂的不对称性，可能是与一个富含气体的伴星系合并的结果。 显示英文摘要

摘要： Near infrared (NIR) and optical surface photometric analyses of the dusty galaxy NGC972 are presented. The photometric profiles in the BVRJHK bands can be fitted with a combination of gaussian and exponential profiles, corresponding to a starburst nucleus and a stellar disk respectively. The exponential scale length in the B-band is 2.8 times larger than in the K-band, which implies a central B-band optical depth as high as 11. A bulge is absent even in the NIR bands and hence the galaxy must be of a morphological type later than the usually adopted Sb type. Relatively low rotational velocity and high gas content also favor a later type, probably Sd, for the galaxy. Only one arm can be traced in the distribution of old stars; the second arm, however, can be traced in the distribution of dust and HII regions. Data suggest a short NIR bar, which ends inside the nuclear ring. The slowly rising nature of the rotation curve rules out a resonance origin of the the nuclear ring. The ring is most likely not in the plane of the galaxy, given its circular appearance in spite of the moderately high inclination of the galaxy. The off-planar nature of the star forming ring, the unusually high fraction (30%) of the total mass in molecular form, the presence of a nuclear starburst and the asymmetry of spiral arms, are probably the result of a merger with a gas-rich companion galaxy.