arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 2005.03038astro-ph.GAastro-ph.SR
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论低金属丰度氮的来源

On the origin of nitrogen at low metallicity

Arpita Roy, Michael A. Dopita, Mark R. Krumholz, Lisa J. Kewley, Ralph S. Sutherland, Alexander Heger

摘要:

了解星系星际介质(ISM)中N/O比的演化是必不可少的,如果我们要完成我们的图片的化学演化的星系在高红移,因为大多数观测校准的O/H隐含地依赖于内在的N/O比。然而,所观察到的N/O比在低O/H时表现出较大的散射,并且强烈依赖于银河系环境。我们发现,迄今无法解释的几个功能的N/O分布在低O/H可以解释的N看到的金属贫星系主要是初级氮,通过前超新星风从快速旋转的大质量恒星($M \gtrsim 10$ M $_\odot$,$v/v_{\rm crit} \gtrsim 0.4$)返回到ISM。这种机制在低O/H下自然产生所观察到的N/O平台。我们表明,在低O/H的N/O的大的散射也自然产生的恒星形成效率的变化。相比之下,N和O主要来自超新星的模型与观测到的丰度分布的拟合非常差。我们建议,我们在低O/H观察到的特殊丰度模式是一个签名,矮星系保留很少的SN喷出物,让他们与典型的风的丰度模式。

英文摘要:

Understanding the evolution of the N/O ratio in the interstellar medium (ISM) of galaxies is essential if we are to complete our picture of the chemical evolution of galaxies at high redshift, since most observational calibrations of O/H implicitly depend upon the intrinsic N/O ratio. The observed N/O ratio, however, shows large scatter at low O/H, and is strongly dependent on galactic environment. We show that several heretofore unexplained features of the N/O distribution at low O/H can be explained by the N seen in metal-poor galaxies being mostly primary nitrogen that is returned to the ISM via pre-supernova winds from rapidly rotating massive stars ($M \gtrsim 10$ M$_\odot$, $v/v_{\rm crit} \gtrsim 0.4$). This mechanism naturally produces the observed N/O plateau at low O/H. We show that the large scatter in N/O at low O/H also arises naturally from variations in star-formation efficiency. By contrast, models in which the N and O come primarily from supernovae provide a very poor fit to the observed abundance distribution. We propose that the peculiar abundance patterns we observe at low O/H are a signature that dwarf galaxies retain little of their SN ejecta, leaving them with abundance patterns typical of winds.

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