根据“自内而外”的星系形成理论，星系的外边缘是星系正在生长的地方，所以对星系外边缘的研究将会为我们提供非常重要的星系形成的信息。但是最近几年基于测光数据的研究发现，在星系外盘的颜色、年龄以及质光比都是越往外越大，与现有的星系形成理论冲突。然而仅仅依靠测光数据很难破除星族年龄、消光和金属丰度的简并，而且拟合误差比较大。因此我们需要积分场单元（IFU）光谱来做进一步更精确的研究。国家天文台现在参与的SDSS-IV MaNGA巡天是现今最大的星系IFU光谱巡天计划，其数据正好适合我们的研究 。因此我们提议利用MaNGA星系样本中的盘星系（>5000个）来研究其外边缘的星族结构。利用如此大的IFU星系样本我们可以更确切的研究盘星系外边缘的统计性质，并可以结合星系环境的信息来限制外盘形成和演化的理论模型。

The outer regions of galaxies provide unique information about formation histories of galaxies. Recent multiband photometric studies (with stellar population synthesis model fitting) revealed very interesting and controversial behaviors of outer disks, e.g. ‘U’ shape color, age and M/L profiles. However, photometric data alone cannot constrain physical parameters such as age, metallicity and dust extinction very well. Integral field unit (IFU) observations are needed to calculate these parameters more accurately.　Fortunately, the SDSS-IV MaNGA survey, which is the largest IFU galaxy survey in the world, provide us more than 5,000 disk galaxies with IFU data. We propose to use the MaNGA data to study the outer regions of disk galaxies. This would be the first resolved spectroscopic study of outer disks using large sample. We would be able to get a more accurate picture of the stellar population distribution in the outer disks than previous studies. We could also constrain outer disk formation and evolution models by combining galaxy environmental information.