Star Formation and Metallicity Gradients in Semi-analytic Models of Disk Galaxy Formation
Jian Fu, Guinevere Kauffmann, Meiling Huang, Robert M. Yates, Sean Moran, Timothy M. Heckman, Romeel Davé, Qi Guo, Bruno M. B. Henriques
备注：
20 pages, 13 figures, accepted for publication in MNRAS. Newer version rephrases the descriptions on the physical recipes and model results according to the refree's report
We have updated our radially-resolved SAMs of galaxy formation, which track both the atomic and molecular gas phases of the ISM. The models are adapted from those of Guo et al. using similar methodology as in Fu et al. and are run on halo merger trees from the MS and MS II with the following main changes: (1) We adopt a simple star formation law where Σ_SFR \propto Σ_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 disk. (3) We include radial gas inflows in disks using a model of the form v_inflow = αr. The models are used to study the radial profiles of star formation rate and gas-phase metallicity in present-day galaxies. The Σ_H2 profiles in L* galaxies place strong constraints on inflow velocities, favouring models where v_inflow~7km/s at a galactocentric radius of 10kpc. 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% 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_sun, as well as the relations between gas-phase metallicity and sSFR in the outer parts of galactic disks. We examine the correlation between 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.
Damped Lyα Absorption Systems in Semi-Analytic Models with Multiphase Gas
我们研究了星系形成半解析模型中阻尼Lyα吸收系统（DLAs）的性质，包括星系盘中冷气体的原子、分子和电离相的分配，以及基于分子气体的恒星形成配方.我们调查了两种方法将气体划分为这些成分：基于压力和基于金属性的配方。我们通过我们的模拟来计算HI柱密度，通过视线来识别DLAs。我们发现，模型与“标准”的气体径向分布-其中的平均特定角动量的气体盘是等于主机暗物质晕-未能再现所观察到的列密度分布的DLAs。这些模型也不能再现速度宽度Δv的分布，相对于高Δv系统，过度产生低Δv。具有“扩展的”径向气体分布的模型-对应于具有更高比角动量的气体盘-能够在红移范围2 < z < 3.5中在柱密度范围19 < log NHI < 22.5内相当好地再现吸收体的柱密度分布。具有基于压力的气体分配的模型还再现了在z 3处观察到的DLAs的线密度、HI气体密度和Δv分布< 3 remarkably well. However all of the models investigated here underproduce DLAs and the HI gas density at z >。如果是这样的话，在0 < z 3的红移区间内，DLAs数和HI气体密度的平坦性来自于< 5 may be due to a cosmic coincidence where the majority of DLA…
