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arXiv 1602.02529astro-ph.GA
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局域宇宙星系的金属丰度梯度:时间演化和径向迁移效应

Metallicity gradients in Local Universe galaxies: time evolution and effects of radial migration

L. Magrini, L. Coccato, L. Stanghellini, V. Casasola, D. Galli

摘要:

我们对盘星系中径向金属丰度梯度形状的了解最近有所提高。相反,对它们的时间演化的理解则更为复杂,因为它需要分析不同年龄的恒星星族,或者对不同红移的星系进行系统的研究。在局域宇宙中,Hii区和行星状星云(PNe)是研究局域宇宙的重要工具,本文利用直接法星云丰度对附近所有旋涡星系(M33,M31,NGC 300和M81)进行了深入研究。我们还首次评估了PN种群的径向迁移。我们分析Hii区域和PN属性:确定PNe中的氧是否是过去星际介质(ISM)组成的可靠示踪剂;均匀化已发表的数据集;估计最古老的恒星星族的迁移;确定整体化学富集和斜率演化。我们证实,氧在PNE是一个可靠的示踪剂过去ISM金属丰度。我们发现,PN梯度平坦或等于那些HII区域。当径向运动可以忽略不计时,该结果提供了梯度的时间演化的直接测量。对于具有主导径向运动的星系,我们提供了梯度演化的上限。最后,总金属含量随时间的增加,在所有的目标星系,早期形态类型有一个更大的增量增量Δ(O/H)比晚型星系。我们的研究结果提供了重要的限制,以区分不同的星系演化的情况下,有利于宇宙学模型与增强反馈超新星。超大型望远镜的出现将使我们能够将星系纳入更广泛的形态和环境中,从而对星系形成和演化情景提出更严格的限制。

英文摘要:

Our knowledge of the shape of radial metallicity gradients in disc galaxies has recently improved. Conversely, the understanding of their time evolution is more complex, since it requires analysis of stellar populations with different ages, or systematic studies of galaxies at different redshifts. In the Local Universe, Hii regions and planetary nebulae (PNe) are important tools to investigate it. We present an in-depth study of all nearby spiral galaxies (M33, M31, NGC300, and M81) with direct-method nebular abundances of both populations. For the first time, we also evaluate the radial migration of PN populations. We analyse Hii region and PN properties to: determine whether oxygen in PNe is a reliable tracer for past interstellar medium (ISM) composition; homogenise the published datasets; estimate the migration of the oldest stellar populations; determine the overall chemical enrichment and slope evolution. We confirm that oxygen in PNe is a reliable tracer for the past ISM metallicity. We find that PN gradients are flatter than or equal to those of Hii regions. When radial motions are negligible, this result provides a direct measurement of the time evolution of the gradient. For galaxies with dominant radial motions, we provide upper limits on the gradient evolution. Finally, the total metal content increases with time in all target galaxies, with early morphological type having a larger increment Delta(O/H) than late-type galaxies. Our findings provide important constraints to discriminate among different galactic evolutionary scenarios, favouring cosmological models with enhanced feedback from supernovae. The advent of extremely large telescopes will allow us to include galaxies in a wider range of morphologies and environments, thus putting firmer constraints to galaxy formation and evolution scenarios.

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