Star formation and metallicity gradients in semi-analytic models of disc galaxy formation
Star formation and metallicity gradients in semi-analytic models of disc galaxy formation
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DOI：
10.1093/mnras/stt1117
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发表时间：
2013-03
影响因子：
4.8
通讯作者：
Jian Fu;G. Kauffmann;Mei-ling Huang;R. Yates;S. Moran;T. Heckman;R. Dav'e;Q. Guo;B. Henriques
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文献类型：
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作者：
Jian Fu;G. Kauffmann;Mei-ling Huang;R. Yates;S. Moran;T. Heckman;R. Dav'e;Q. Guo;B. Henriques
我们更新了星系形成的径向解析半解析模型（SAM），该模型跟踪星际介质的原子和分子气相。这些模型改编自Guo 等人的模型。使用与 Fu 等人类似的方法。并在来自 Millennium 和 Millennium-II 模拟的 halo 合并树上运行，主要变化如下。 (1) 我们采用简单的恒星形成定律Sigma(SFR) Sigma(H2)。 （2）我们将超新星产生的重元素直接注入到晕热气体中，而不是先将它们与盘中的冷气体混合。 (3) 我们使用 v(inflow) = alpha r 形式的模型将圆盘中的径向气体流入包括在内。该模型用于研究当今星系中恒星形成速率和气相金属丰度的径向剖面。 L-* 星系中分子气体的表面密度分布对流入速度有很大的限制，有利于在 10 kpc 的星系中心半径下 v（流入）类似于 7 km s(-1) 的模型。径向气体流入对气相和恒星金属丰度梯度影响不大，直接注入晕气体中的金属分数比与冷气体混合的金属分数对气相和恒星金属丰度梯度的影响要大得多。早期时期从星系中喷出的金属导致预富集气体的晚期流入和当今气相金属丰度梯度的平坦化。将 80% 的金属注入晕气体中的方案很好地拟合了恒星质量大于 10(10) M 圆点的星系中观察到的平坦金属丰度梯度，以及气相金属丰度与星系盘外部特定恒星形成速率之间的关系。我们研究了气相金属丰度梯度与整体星系特性之间的相关性，发现它与星系的核球与总比率的相关性最强。这是因为当星系合并期间形成核球时，气体被消耗，然后气相金属丰度梯度由新吸积的气体设定。
We have updated our radially resolved semi-analytic models (SAMs) of galaxy formation, which track both the atomic and molecular gas phases of the interstellar medium. The models are adapted from those of Guo et al. using similar methodology as by Fu et al. and are run on halo merger trees from the Millennium and Millennium-II simulations with the following main changes. (1) We adopt a simple star formation law Sigma(SFR) Sigma(H2). (2) We inject the heavy elements produced by supernovae directly into the halo hot gas, instead of first mixing them with the cold gas in the disc. (3) We include radial gas inflows in discs using a model of the form v(inflow) = alpha r. The models are used to study the radial profiles of star formation rate and gas-phase metallicity in present-day galaxies. The surface density profiles of molecular gas in L-* galaxies place strong constraints on inflow velocities, favouring models where v(inflow) similar to 7 km s(-1) at a galactocentric radius of 10 kpc. Radial gas inflow has little influence on gas-phase and stellar metallicity gradients, which are affected much more strongly by the fraction of metals that are directly injected into the halo gas, rather than mixed with the cold gas. Metals ejected out of the galaxy in early epochs result in late infall of pre-enriched gas and flatter present-day gas-phase metallicity gradients. A prescription in which 80 per cent of the metals are injected into the halo gas results in good fits to the flat observed metallicity gradients in galaxies with stellar masses greater than 10(10) M-circle dot, as well as the relations between gas-phase metallicity and specific star formation rate in the outer parts of galactic discs. We examine the correlation between the gas-phase metallicity gradient and global galaxy properties, finding that it is most strongly correlated with the bulge-to-total ratio of the galaxy. This is because gas is consumed when the bulge forms during galaxy mergers, and the gas-phase metallicity gradient is then set by newly accreted gas.