论金属丰度梯度对主要干合并的生存
On the survival of metallicity gradients to major dry-mergers
摘要：
使用一个大的套件的星系与各种浓度和金属丰度梯度，我们研究的非耗散（“干”）等质量合并的演变。我们生成这些模拟的目的是探索干合并中的金属丰度梯度如何取决于合并中涉及的星系的结构和金属丰度梯度。具体地说，我们想回答：干合并会导致金属丰度梯度，如在本机宇宙中的椭圆星系中观察到的那样吗？干合并是否总是导致初始的平坦化（即，合并前）梯度？从这个模型中，我们得出结论：残余和初始星系斜率的比值范围很广，最大值大于1（只有当同伴的斜率是祖先的两倍时，才会产生大于1的值）。对于具有相同初始金属丰度斜率的两个椭圆形之间的合并（即，相等的伴星和星系斜率），剩余的彗星的金属丰度轮廓，最终的梯度约为初始梯度的0.6倍。如果伴随的斜率足够陡，椭圆星系可以保持其合并前的金属丰度梯度。扁平的数量既不取决于祖先的轨道特征，也不取决于它们的初始浓度。鉴于合并的结果的多样性，我们得出结论，干合并不违反任何观测约束的金属丰度梯度的系统特征，在当地的椭圆。事实上，干合并可能是很重要的，在我们的模拟结果的背景下，可以解释大规模的椭圆形和相对缺乏的大规模椭圆形的金属丰度梯度和梯度的大规模分散。
英文摘要：
Using a large suite of galaxies with a variety of concentrations and metallicity gradients, we study the evolution of non-dissipative ("dry") equal mass mergers. Our purpose in generating these simulations is to explore how the metallicity gradient in dry mergers depends on the structure and metallicity gradients of the galaxies involved in the merger. Specifically, we would like to answer: Could dry mergers lead to metallicity gradients as observed in elliptical galaxies in the local Universe? Do dry mergers always lead to a flattening of the initial (i.e., pre-merger) gradient? From this modeling, we conclude that: The ratio of the remnant and the initial galaxy slopes span a wide range of values, up to values greater than 1 (with values greater than one resulting only when companions have gradients twice the progenitor). For a merger between two ellipticals having identical initial metallicity slopes (i.e., equal companion and galaxy slopes), the metallicity profile of the remnant flattens, with a final gradient about 0.6 times the initial one. Ellipticals can maintain their original pre-merger metallicity gradient if the companion slope is sufficiently steep. The amount of flattening neither depends on the characteristics of the orbit of the progenitors or on their initial concentration. Given the diversity in outcomes of the mergers, we conclude that dry mergers do not violate any observational constraints on the systematic characteristics of metallicity gradients in local ellipticals. In fact, dry mergers may be important within the context of the results of our simulations and may explain the large scatter in gradients for massive ellipticals and the relative paucity of massive ellipticals with no or shallow metallicity gradients.
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