星流的搜寻

Searching for the Stellar Streams

在冷暗物质的宇宙学模型框架里,银河系(尤其是银晕)至少部分起源于对周围卫星星系的吸积。随着新技术和新设备的不断应用,大规模巡天项目的成功实施使天文学家获得了越来越多、越来越全面的关于银河系的数据。通过对这些数据进行分析,天文学家发现了很多星流的候选体,为银河系的等级并合理论提供了观测上的证据。随着对星流研究的扩大和深入,人们对银河系及其结构和起源的了解也越来越详细。介绍了搜寻星流的方法,以及基于这些方法获得的星流研究结果。

Within the ACDM model, the structure is formed hierarchically. Considering our Galaxy within this model, it is formed at least partly by accreting the satellite galaxies. In the process of the accretion, the satellite galaxies are torn into stellar streams by the Galactic gravitational tidal force. The number, property and structure of the stellar streams help understanding the structure and the formation history of our Galaxy, and indirectly examine whether the model of hierarchical structure formation is true. This paper overviews the methods to search for stellar streams and the results of various searches. The methods are classified into two main types. One type of methods is based on overdensity in the geometrical space caused by stellar streams which can exist for relatively short time, which is thus effective for finding young stellar streams. The other type of methods looks for the clustering structure in the phase space with the parameters being either velocity or integrals of motions, even in the actionangle space. Stellar streams can still be clustering in the phase space after the evidence in geometrical space disappears, which makes the phase space method better in searching for ghost stellar streams. In practice, both the geometrical and phase spaces are applied to search for and confirm the stellar streams. The Sagittarius stream presents itself with abundant evidences, including the overdensity of various types of objects such as Mtype red giants. Moreover, the detailed study of the Sagittarius stream reveals the potential and structure of the Galactic halo. With the development of observational techniques and largescale surveys, more and more stellar streams and candidates are found, e.g. the Magellanic stream, the Monoceros ring and the Virgo stream. Future projects such as GAIA and Guoshoujing telescope will help to discover more stellar streams in our Galaxy.