The Properties Of Stars Along The Sagittarius Tidal Tails And The Relation Between Sgr And Virgo Overdensity

In this master thesis,based on the massive spectrum data obtained by SDSS and LAMOST spectroscopic survey,we do the research on kinematics and chemistry abun-dances of the Milky Way and its neighboring dwarf galaxy Sagittarius galaxy,providing new clues for understanding the formation and evolution of the Milky Way and Sagit?tarius dwarf galaxy.Firstly,from SDSS DR9 database we get?22000 RGB star spectra data.We used the improved theoretical model along the Sgr stream selecting 1100 sample.Compared with RHB stars,RGB stars have a larger sample,and extend to metal poor component[Fe/H]?-3.0dex.In particular,this RGB sample has a significant number of stars in the second wrap of the leading stream of the Sgr?leading arm 2?,and this provide a good opportunity to understand the properties of the leading stream.We derive a metallicity gradient of-?2.3±0.5?×10-3dex deg-1 in leading arm 2 for the first time,of-?1.6±0.4?x 10-6dex deg-1 for the leading arm 1,and of-?1.3d±0.3?x.10-3dex deg₁ for the trailing arm 1.We check the distribution of Sgr stars in phase space and find a velocity dispersion of?21.5km/s for leading arm 1.Finally,combined data from SDSS and LAMOST,we identify a possible new branch in leading arm 1.Secondly,we selected 32 RGB stars belonging to Virgo overdensity from SDSS DR9 database?Based on difference between velocity,we devided these stars into two group-s?21 stars whose speed is low belong to VSS,and other high speed stars belong to Feature C?The mentallicity distribution of stars belonging to VSS has two peaks at-1.2dex and-1.9dex,respectively.The mentallicity distribution of stars belonging to Feature C is disperse.The streams of Sagittarius is close to Virgo overdensity.So we analyse the relation between Sagittarius and Virgo overdensity.Stars in VSS have similar velocity and mentallicity with trailing arm 1,so we infer VSS may come from trailing arm 1?It is a portion cutting off from trailing arm 1 and moving in its own track.Stars in Feature C have a disperse mentallicity distribution and their speed is far higher than stream of Sagittarius.Therefore,Feature C is more likely to be the debris of merger between the Milky Way and another dwarf galaxy.