The Evolution and Star Formation History of M33
  We construct a parameterized model to explore the main properties of the star formation history of M33. We assume that the disk originates and grows by the primordial gas infall and adopt the simple form of gas accretion rate with one free parameter, the infall time-scale. We also include the contribution of gas outflow process. A major update of the model is that we adopt a molecular hydrogen correlated star formation law and calculate the evolution of the atomic and molecular gas separately. Comparisons between the model predictions and the observational data show that the model predictions are very sensitive to the adopted infall time-scale, while the gas outflow process mainly influences the metallicity profile. The model adopting a moderate outflow rate and an inside-out formation scenario can be in good agreement with most of observed constraints of M33 disk. We also compare the model predictions based on the molecular hydrogen correlated star formation law and that based on the Kennicutt star formation law. Our results imply that the molecular hydrogen correlated star formation law should be preferred to describe the evolution of the M33 disk, especially the radial distributions of both the cold gas and the stellar population. 
Xiaoyu Kang, Ruixiang Chang, Jun Yin, Jinliang Hou, Fenghui Zhang, Yu   Zhang and Zhanwen Han
astro-ph.CO astro-ph.GA