星系缩小和氧和氮丰度的红移演化：N/H-O/H图中散射的起源
Galaxy downsizing and the redshift evolution of oxygen and nitrogen abundances: origin of the scatter in the N/H-O/H diagram
摘要：
在Sloan数字巡天观测中，考虑了星系恒星质量从10^11.3 M_sun到10^10.2 M_sun的4个区间，氧和氮丰度随红移的变化.我们已经测量了它们的线通量，并使用最近的校准推导出O和N丰度。O和N丰度随红移的演化清楚地显示了星系缩小效应，在早期，高质量星系的富集（因此是恒星形成）停止，并在后期转移到低质量星系。本文对N/H-O/H图中散射的来源进行了探讨。最大质量的星系，O和N富集和恒星形成已经停止，占据了N/H-O/H图中的窄带，定义了上包络。质量较小的星系在当前时期仍在进行恒星形成，它们在N/H-O/H图中向下移动，朝向较低的N/H值。这种向下移动是由N和O富集之间的时间延迟引起的。这种时间延迟与星系中不同的恒星形成历史一起是N/H-O/H图中大的散射的原因。
英文摘要：
The oxygen and nitrogen abundance evolutions with redshift of emission-line galaxies in the Sloan Digital Sky Survey are considered for four intervals of galaxy stellar masses, ranging from 10^11.3 M_sun to 10^10.2 M_sun. We have measured their line fluxes and derived the O and N abundances using recent calibrations. The evolution of O and N abundances with redshift clearly shows the galaxy downsizing effect, where enrichment (and hence star formation) ceases in high-mass galaxies at earlier times and shifts to lower-mass galaxies at later epochs. The origin of the scatter in the N/H - O/H diagram has been examined. The most massive galaxies, where O and N enrichment and star formation has already stopped, occupy a narrow band in the N/H -- O/H diagram, defining an upper envelope. The less massive galaxies which are still undergoing star formation at the current epoch are shifted downwards, towards lower N/H values in the N/H - O/H diagram. This downward shift is caused by the time delay between N and O enrichment. This time delay together with the different star formation histories in galaxies is responsible for the large scatter in the N/H -- O/H diagram.
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