利用星团研究星系M31和M33的相互作用和演化过程

The recent studies show that the formation and evolution process (star, globular clusters, gas …) of the nearby galaxies are still not clear. The Panoramic Andromeda Archaeological Survey (PanDAS) of Andromeda galaxy (M31) and the Triangulum Galaxy (M33) was conducted by McConnachie with the CFHT 3.6m Telescope at Hawaii in the year of 2008. Over 400 deg^2 field was observed (deep to 25.5 mag in g band) and very complicated substructures in the halo of M31 galaxy were discovered: nearly 30 dwarf satellite galaxies, dozens of halo globular clusters and extended clusters are distributed in the outer halo to ~150 kpc from the center of M31. It is also found the two galaxies M31/M33 were actually connected by the star and gas stream, which has been proved by the recent HI observations. It reveals the possible interactions between M31 and M33 galaxies and the giant star streams were produces by the strong tidal forces. The study shows that the M31/M33 interaction is still going on in a few giga years. It can be seen that the galaxy-interactions are much more complicated than that we expect and such discoveries may change the understandings of the fundamental nature of the Universe. In our project, we propose to investigate the interaction (substructures), formation and evolution of M31/M33 sub-group, which are the nearest two giant spirals in our local group. The globular/star cluster systems of the two galaxies are good tracers to study the dynamics of the giant star streams and the substructures. For this study, the Xinglong 2.16m/Lijiang 2.4m/MMT 6.5m/LAMOST telescopes will probably be used for our spectroscopic observations. The radial velocities and Lick absorption-line indices can thus be measured from the spectroscopes and the ages, metallicities, extinctions and masses of the star clusters in both M31 and M33 galaxies can be fitted with the SSP models. These parameters will be used as the input physical parameters for the numerical simulations.

近邻星系的形成和演化过程中至今还有很多未解之谜。2008年，McConnachie领导的团队利用CFHT3.6米望远镜对本星系群中M31（仙女座星系）和M33（三角座星系）进行了深到g=25.5等的全景考古巡天(PAndAS)。他们发现M31周围存在多处结构复杂的大尺度恒星流，弥漫在M31的外晕以及两星系之间；M31周围30个卫星矮星系以及几十个球状星团分布在距星系中心150 kpc的晕内，两星系间的恒星和气体成分也连接在一起（中性氢观测也发现此结构），表明这两个巨星系曾发生过剧烈的相互作用。本项目以这两个距我们最近的漩涡星系为研究对象，利用其内部和晕里的星团来模拟和追踪恒星流的动力学性质和星系的形成和演化过程。我们将使用兴隆2.16m/丽江2.4m/MMT6.5m/LAMOST等望远镜进行星团的光谱观测来计算视向速度,并利用谱指数来拟合星族的年龄、金属丰度和质量作为输入参量进行模拟。

近场宇宙学近年来是天文学研究的热点问题，通过全景仙女座星系考古巡天(PAndAS)发现M31周围存在多处结构非常复杂的大尺度恒星流以及子结构，周围周围30个卫星矮星系以及几十个球状星团分布在距星系中心150 kpc的晕内,表明这两个巨星系曾发生过剧烈的相互作用。本项中我们使用兴隆2.16m, 丽江2.4m, MMT 6.5m, LAMOST等望远镜对其内部星团系统进行光谱/测光观测来计算视向速度,并利用谱指数和测光数据拟合星族年龄、金属丰度和质量。我们对M33中671个星团进行了SED拟合，利用PARSEC简单星族模型得到了其年龄，金属丰度和质量。结果显示只有205个（31%）老于20亿年，这比M31中的年老的星团数量比例（56%）要少得多，说明M33中是以年轻的星团（<10亿年）为主。我们调研了M33/M31/银河系/大麦哲伦云的星团质量，平均值分别为log(M/Msun)=4.25, 5.43, 2.72, 4.18，其中疏散星团/球状星团的比例在银河系最高，在M31最低。我们利用6.5米多镜面望远镜MMT的红通道光谱仪对M31中22个星团进行了光谱观测，利用Lick谱指数和不同的模型进行拟合以及测光的SED拟合。结果表明，谱指数和SED拟合结合的方法比单独的使用谱指数或SED拟合的方法更可靠，且拟合精度更高。我们发现紫外波段FUV/NUV观测数据相比于其它波段对于SED拟合年龄和金属丰度结果的影响都更加显著，因此高质量的紫外观测数据对于星族分析是非常有帮助的。这些结果对星系形成、演化和相互作用都非常重要，对于星族合成模型的拟合也非常有帮助。项目期间共发表SCI论文13篇（第一作者4篇），IAUS会议文集1篇。