盘星系并合的数值模拟

Simulations on Disky Galaxy Merger

使用一系列的模拟,包括了不同的轨道参数、主并合与小并合,以及不同的恒星盘自旋角动量与轨道角动量的耦合方式,来研究盘星系的并合过程中,顺行交会和逆行交会对并合过程会产生怎样的影响.这些影响包括并合时标、轨道形态、星系的恒星及暗物质成分剥离效率、星系的形态变化,以及形成的潮汐结构等.研究发现,由于在并合过程的前期,逆行并合的恒星剥离效率要明显小于顺行并合,因此会形成小得多的潮汐结构.但与通常认为的相反的是,与顺行并合相比,逆行并合并没有显著改变轨道形态和增大并合时标,对恒星成分的剥离效率也没有显著的影响.与顺行与否相比,潮汐半径在小并合时,卫星星系恒星成分被潮汐剥离的过程中扮演着更重要的角色,潮汐半径与恒星盘标长相等的时刻可以被认为是卫星星系恒星盘瓦解的时刻.

We do a series of simulations, including different orbit parameters, merger mass ratio, mass resolution, as well as different coupling of galaxy spin angular momen-- turn and orbit angular momentum, to test how the coupling can affect the merger time scale, orbit property, tidal stripping, morphology evolution of stellar disk, and tidal structure. We find that since the tidal stripping efficiency in earlier stage of retrograde encounter is lower than that in prograge encounter, the retrograde encounter thus does form a much smaller tidal structure. However, contrary to popular belief, the retrograde encounter does not have a significant difference with the prograde encounter in merger time scale, orbit decay, and even in global tidal disruption. Comparing with prograde and retrograde, tidal radius plays a more important role in tidal stripping. The time when tidal radius equals to stellar disk scale length can be used to identify the moment when stellar disk is dramatically tidal disrupted.