银盘径向丰度梯度及冷气体的演化

Evolution of the Radial Abundance Gradient and Cold Gas along the Milky Way Disk

为了理解银盘的径向丰度梯度形成机制及冷气体演化,构建了银盘化学演化模型.模型中采用了与分子氢相关的恒星形成律,分开计算了分子氢和原子氢的质量面密度演化,并将模型预言和观测到的各物理量径向轮廓进行了比较.结果表明,模型预言对所采用的内落时标非常敏感,采用与分子氢相关的恒星形成律的模型能够较好地符合银盘基本的观测特征,尤其是能够自然地得到银盘的径向氧丰度梯度和冷气体的径向面密度轮廓.采用瞬时或非瞬时循环假设对冷气体的演化影响不大,在气体密度较低的情况下更是如此.

We have constructed a phenomenological model of the chemical evolution of the Milky Way disk, and treated the molecular and atomic gas separately. Using this model, we explore the radial profiles of oxygen abundance~ the surface density of cold gas~ and their time evolutions. It is shown that the model predictions are very sensitive to the adopted infall time-scale. By comparing the model predictions with the observations, we find that the model adopting the star formation law based on H2 can properly predict the observed radial distributions of cold gas and oxygen abundance gradient along the disk. We also com- pare the model results with the predictions of the model which adopts the instantaneous recycling approximation （IRA）, and find that the IRA assumption has little influence on the model results, especially in the low-density gas region.