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arXiv 1306.2316astro-ph.CO
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致密早型星系中的动力学质量与恒星质量：恒星初始质量函数系统变化的进一步证据

Dynamical Versus Stellar Masses in Compact Early-Type Galaxies: Further Evidence for Systematic Variation in the Stellar Initial Mass Function

Charlie Conroy, Aaron A. Dutton, Genevieve J. Graves, J. Trevor Mendel, Pieter G. van Dokkum

备注：
6 pages, 4 figures, ApJL accepted
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摘要：

几个独立的证据表明，恒星的初始质量函数（IMF）在早期型星系变得越来越“底重”的星系质量和/或速度色散，西格玛。在这里，我们考虑的证据IMF变化的样本相对紧凑的早期型星系从斯隆数字巡天。这些星系有足够高的恒星密度，在一个有效半径内，暗晕可能对总动力学质量Mdyn有很小的贡献。我们适合我们详细的恒星星族合成模型，这些星系的堆栈吸收线光谱在箱中的西格玛，并找到证据，从IMF敏感的光谱特征底部重IMF在高西格玛。我们也适用于简单的“质量跟随光”的动力学模型相同的数据，并发现Mdyn是显着高于预期，如果这些星系的恒星为主，并有一个普遍的银河系IMF。因此，采用Mdyn M_* 意味着IMF在高sigma时“更重”。最重要的是，这两种技术之间推断的IMF变化的定量非常相似，在质量上在0.1 dex内一致。当应用于相同的数据时，两种独立技术之间的一致性为IMF作为早期星系速度弥散函数的系统变化提供了令人信服的证据。任何替代的解释都必须重现动力学和基于恒星星族的技术的结果。

英文摘要：

Several independent lines of evidence suggest that the stellar initial mass function (IMF) in early-type galaxies becomes increasingly `bottom-heavy' with increasing galaxy mass and/or velocity dispersion, sigma. Here we consider evidence for IMF variation in a sample of relatively compact early-type galaxies drawn from the Sloan Digital Sky Survey. These galaxies are of sufficiently high stellar density that a dark halo likely makes a minor contribution to the total dynamical mass, Mdyn, within one effective radius. We fit our detailed stellar population synthesis models to the stacked absorption line spectra of these galaxies in bins of sigma and find evidence from IMF-sensitive spectral features for a bottom-heavy IMF at high sigma. We also apply simple `mass-follows-light' dynamical models to the same data and find that Mdyn is significantly higher than what would be expected if these galaxies were stellar dominated and had a universal Milky Way IMF. Adopting Mdyn M_* therefore implies that the IMF is `heavier' at high sigma. Most importantly, the quantitative amount of inferred IMF variation is very similar between the two techniques, agreeing to within 0.1 dex in mass. The agreement between two independent techniques, when applied to the same data, provides compelling evidence for systematic variation in the IMF as a function of early-type galaxy velocity dispersion. Any alternative explanations must reproduce both the results from dynamical and stellar population-based techniques.

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