Ancient and Recent Galaxy Mergers

古代和近代星系合并过去星系的碰撞和合并似乎在决定当今星系的形状和动力学方面起了重要作用。尽管星系合并的数量随着时间的推移而减少，但仍有一些这样的合并仍在发生，并为我们了解过去的演化过程提供了宝贵的线索。施韦泽博士正在确定附近星系中古代和近代合并事件的日期。年轻的球状星团的发现显然是在合并过程中形成的，这使得一种测定合并事件本身年代的新方法成为可能。由于球状星团有同时期的恒星，所以比整个星系更容易确定年代。Schweizer博士正在进行六个项目：(1)分析六个合并星系的图像，在其中寻找年轻到中年的球状星团；(2)建立球状星团年表；(3)确定集群的大尺度空间分布；(4)测量这些团簇的金属丰度和年龄；(5)绘制三个并合星系中恒星和气体的速度图，确定并合动力学；(6)在NGC 7252中寻找残留的星系风和可能的大规模激波锋。这些项目解决了星系起源、球状星团的年龄和金属丰度、合并残留物中奇怪旋转核心的形成以及合并过程中气体的命运等关键问题。

Ancient and recent galaxy mergersFrancois SchweizerCollisions and mergers of galaxies in the past seem to have played a major role in determining the shapes and dynamics of present day galaxies. Though the number of galactic mergers has declined with time, a few such mergers are still occurring and offer us valuable clues to past evolutionary processes. Dr. Schweizer is determining the dates of ancient and recent merger events in nearby galaxies. Discoveries of young globular star clusters apparently formed during mergers have made possible a new method for dating the merger events themselves. Because of the coeval stars, globular clusters are more easily dated than whole galaxies. Dr. Schweizer is conducting six projects: (1) an analysis of images of six merger galaxies to search young to intermediate age globular clusters in them; (2) establish a globular cluster chronology; (3) determine the large scale spatial distribution of the clusters; (4) measure metallicities and ages of these clusters; (5) map the velocities of the stars and gas in three merger galaxies to determine the merger dynamics; and (6) search for a remnant galactic wind and possible large scale shock fronts in the merger remnant NGC 7252. These projects address key questions on the origins of galaxies, the ages and metallicities of globular clusters in them, the formation of oddly rotating cores in merger remnants, and the fate of gas during mergers.