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arXiv 1602.02773astro-ph.GA
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环境如何通过剥离和形成历史影响星系金属丰度:来自Illustris模拟的教训

How Environment Affects Galaxy Metallicity through Stripping and Formation History: Lessons from the Illustris Simulation

Shy Genel

摘要:

最近的研究发现,在更丰富的环境中,星系的金属丰度更高。然而,目前尚不清楚金属丰度与环境的依赖性是否仅仅是环境依赖性形成历史的间接结果,或者是直接影响金属丰度的环境相关过程的间接结果。在这里,我们提出了第一个详细的研究,在宇宙流体动力学模拟,特别是Illustris模拟的金属性环境的相关性。Illustris星系显示类似的关系,观察到的。利用我们的知识模拟形成的历史,并利用大的模拟量,我们构建星系样本的卫星和中心相匹配的形成历史。这使我们能够发现,~1/3的金属性-环境相关性是由于不同的形成历史在不同的环境。这是卫星(特别是在密度较高的环境中)具有较低的z=0恒星形成率(SFR)和较老的恒星年龄(即使在给定的z=0 SFR)的综合效应。然而,大部分差异(约2/3)是由卫星星系的恒星形成盘的较高浓度引起的,因为这使它们的SFR加权金属丰度偏向内部,更富含金属的部分。与一个新定义的量,“径向平均”的金属丰度,它捕获的金属丰度的配置文件,但独立的SFR配置文件,卫星和中心的金属丰度成为环境独立的,一旦他们在形成历史中匹配。我们发现,环星系金属丰度(定义为快速流入的气体周围的维里半径),而对环境敏感,有没有可测量的影响,星系内的恒星形成气体的金属丰度。

英文摘要:

Recent studies have found higher galaxy metallicities in richer environments. It is not yet clear, however, whether metallicity-environment dependencies are merely an indirect consequence of environmentally dependent formation histories, or of environment related processes directly affecting metallicity. Here, we present a first detailed study of metallicity-environment correlations in a cosmological hydrodynamical simulation, in particular the Illustris simulation. Illustris galaxies display similar relations to those observed. Utilizing our knowledge of simulated formation histories, and leveraging the large simulation volume, we construct galaxy samples of satellites and centrals that are matched in formation histories. This allows us to find that ~1/3 of the metallicity-environment correlation is due to different formation histories in different environments. This is a combined effect of satellites (in particular, in denser environments) having on average lower z=0 star formation rates (SFRs), and of their older stellar ages, even at a given z=0 SFR. Most of the difference, ~2/3, however, is caused by the higher concentration of star-forming disks of satellite galaxies, as this biases their SFR-weighted metallicities toward their inner, more metal-rich parts. With a newly defined quantity, the 'radially averaged' metallicity, which captures the metallicity profile but is independent of the SFR profile, the metallicities of satellites and centrals become environmentally independent once they are matched in formation history. We find that circumgalactic metallicity (defined as rapidly inflowing gas around the virial radius), while sensitive to environment, has no measurable effect on the metallicity of the star-forming gas inside the galaxies.

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