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首页> 外文期刊>Astronomy and astrophysics >Abundance patterns in early-type galaxies: is there a “knee” in the [Fe/H] vs. [α/Fe] relation?
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Abundance patterns in early-type galaxies: is there a “knee” in the [Fe/H] vs. [α/Fe] relation?

机译：早期类型星系中的丰度模式：[Fe / H]与[α/ Fe]关系中是否存在“膝盖”？

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Early-type galaxies (ETGs) are known to be enhanced in α elements, in accordance with their old ages and short formation timescales. In this contribution we aim to resolve the enrichment histories of ETGs. This means we study the abundance of Fe ([Fe/H]) and the α-element groups ([α/Fe]) separately for stars older than 9.5 Gyr ([Fe/H]o, [α/Fe]o) and for stars between 1.5 and 9.5 Gyr ([Fe/H]i, [α/Fe]i). Through extensive simulation we show that we can indeed recover the enrichment history per galaxy. We then analyze a spectroscopic sample of 2286 early-type galaxies from the SDSS selected to be ETGs. We separate out those galaxies for which the abundance of iron in stars grows throughout the lifetime of the galaxy, i.e. in which [Fe/H]o< [Fe/H]i. We call those consistent with self-enrichment, while the others must have experienced some mergers or significant gas accretion. We confirm earlier work where the [Fe/H] and [α/Fe] parameters are correlated with the mass and velocity dispersion of ETGs. We emphasize that the strongest relation is between [α/Fe] and age. This relation falls into two regimes, one with a steep slope for old galaxies and one with a shallow slope for younger ETGs. The vast majority of ETGs in our sample do not show the “knee” in the plot of [Fe/H] vs. [α/Fe] commonly observed in local group galaxies. This implies that for the vast majority of ETGs, the stars younger than 9.5 Gyr are likely to have been accreted or formed from accreted gas. The properties of the intermediate-age stars in accretion-dominated ETGs indicate that mass growth through late (minor) mergers in ETGs is dominated by galaxies with low [Fe/H] and low [α/Fe]. The method of reconstructing the stellar enrichment histories of ETGs introduced in this paper promises to constrain the star formation and mass assembly histories of large samples of galaxies in a unique way.
机译：已知早期类型的星系（ETG）根据其年龄和较短的形成时间尺度而增强了α元素。在此贡献中，我们旨在解决ETG的丰富历史。这意味着对于9.5 Gyr以上的恒星（[Fe / H] o，[α/ Fe] o），我们分别研究了Fe（[Fe / H]）和α-元素组（[α/ Fe]）的丰度。对于1.5至9.5 Gyr（[Fe / H] i，[α/ Fe] i）之间的恒星。通过广泛的模拟，我们表明我们确实可以恢复每个星系的浓缩历史。然后，我们从被选为ETG的SDSS中分析了2286个早期类型星系的光谱样本。我们将星系中铁的丰度在整个银河系的生命周期中增长的那些星系分开，即[Fe / H] o <[Fe / H] i。我们称那些与自我充实相一致的人，而其他人则必须经历过一些合并或大量天然气的积累。我们确认了早期的工作，其中[Fe / H]和[α/ Fe]参数与ETG的质量和速度分散相关。我们强调，最强的关系是在[α/ Fe]与年龄之间。这种关系分为两种状态，一种对于旧星系具有陡峭的斜率，对于一种年轻的ETG具有一种浅斜率。在我们的样本中，绝大多数ETG在[Fe / H]与[α/ Fe]相对于局部星系星系中常见的图中没有显示“膝盖”。这意味着，对于绝大多数ETG，小于9.5 Gyr的恒星很可能是由积聚的气体积聚或形成的。在以增生为主的ETG中，中年恒星的性质表明，通过ETG后期（次要）合并的质量增长主要由低[Fe / H]和低[α/ Fe]的星系决定。本文介绍的重建ETG恒星富集历史的方法有望以独特的方式限制大样本星系的恒星形成和质量装配历史。

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