星系相互作用和合并的稀释峰、金属丰度演化和定年
The dilution peak, metallicity evolution, and dating of galaxy interactions and mergers
摘要：
在盘状星系的相互作用过程中，会引起从外盘到内千秒差距的强烈气体流入。这种相对低金属含量气体的流入稀释了环核气体的金属含量。我们已经研究了这个过程的几个方面，如稀释的时间和持续时间及其与诱导恒星形成的相关性。我们分析了主要的（1：1）富含气体的相互作用和合并，跨越一系列的初始轨道特征。我们的模型中包括了恒星形成和SNe的金属富集。我们的研究结果表明，最强的趋势是恒星形成率和核区域金属的稀释之间;即，恒星形成的中心爆发越强烈，气体就被稀释得越多。这种趋势来自于两个盘的外部区域相对金属贫乏的气体的强烈流入，这为激烈的恒星形成提供了燃料，并在一段时间内降低了整体金属丰度。强烈的流入发生在大约10^8年或更短的时间尺度上，最强烈的恒星形成和最低的气相金属丰度通常出现在第一次近心点通过之后。随着恒星形成的进行和合并的进展，稀释减少，富集成为主导-最终将环核气体的金属丰度提高到高于合并星系的初始金属丰度的水平。“飞越”--相互作用但不合并的配对--也会导致一些稀释。我们甚至在合并或“飞越”的早期看到一些稀释，因此在我们的模拟中没有观察到核金属丰度和分离之间的强烈趋势，直到合并进行得很好。我们还分析了O和Fe富集的ISM，并表明，α/Fe比的演变，以及稀释的中心气体金属丰度，可以用作时钟的“约会”的相互作用。
英文摘要：
Strong inflows of gas from the outer disk to the inner kiloparsecs are induced during the interaction of disk galaxies. This inflow of relatively low-metallicity gas dilutes the metallicity of the circumnuclear gas. We have investigated several aspects of the process as the timing and duration of the dilution and its correlation with the induced star formation. We analysed major (1:1) gas-rich interactions and mergers, spanning a range of initial orbital characteristics. Star formation and metal enrichment from SNe are included in our model. Our results show that the strongest trend is between the star formation rate and the dilution of the metals in the nuclear region; i.e., the more intense the central burst of star formation, the more the gas is diluted. This trend comes from strong inflows of relatively metal-poor gas from the outer regions of both disks, which fuels the intense star formation and lowers the overall metallicity for a time. The strong inflows happen on timescales of about 10^8 years or less, and the most intense star formation and lowest gas phase metallicities are seen generally after the first pericentre passage. As the star formation proceeds and the merger advances, the dilution reduces and enrichment becomes dominant - ultimately increasing the metallicity of the circumnuclear gas to a level higher than the initial metallicities of the merging galaxies. The "fly-bys" - pairs that interact but do not merge - also cause some dilution. We even see some dilution early in the merger or in the "fly-bys" and thus do not observe a strong trend between the nuclear metallicities and separation in our simulations until the merger is well advanced. We also analyse the O and Fe enrichment of the ISM, and show that the evolution of the alpha/Fe ratios, as well as the dilution of the central gas metallicity, can be used as a clock for "dating" the interaction.
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