AN EVOLUTIONARY MODEL FOR COLLAPSING MOLECULAR CLOUDS AND THEIR STAR FORMATION ACTIVITY. II. MASS DEPENDENCE OF THE STAR FORMATION RATE

作者：Zamora Aviles Manuel^*; Vazquez Semadeni Enrique

来源：Astrophysical Journal, 2014, 793(2): 84.

DOI：10.1088/0004-637X/793/2/84

• galaxies: star formation
• gravitation
• H II regions
• ISM: clouds
• ISM: kinematics and dynamics
• radiation: dynamics
• stars: evolution
• stars: formation
• stars: massive
• turbulence

We discuss the evolution and dependence on cloud mass of the star formation rate (SFR) and efficiency (SFE) of star-forming molecular clouds (MCs) within the scenario that clouds are undergoing global collapse and that the SFR is controlled by ionization feedback. We find that low-mass clouds (M-max less than or similar to 10(4) M-circle dot) spend most of their evolution at low SFRs, but end their lives with a mini-burst, reaching a peak SFR similar to 10(4) M-circle dot Myr(-1), although their time-averaged SFR is only %26lt; SFR %26gt; similar to 10(2) M-circle dot Myr(-1). The corresponding efficiencies are SFEfinal less than or similar to 60% and %26lt; SFE %26gt; less than or similar to 1%. For more massive clouds (M-max less than or similar to 10(5) M-circle dot), the SFR first increases and then reaches a plateau because the clouds are influenced by stellar feedback since earlier in their evolution. As a function of cloud mass, %26lt; SFR %26gt; and %26lt; SFE %26gt; are well represented by the fits %26lt; SFE %26gt; approximate to 100(1 + M-max/1.4 x 10(5) M-circle dot)(1.68) M-circle dot Myr(-1) and %26lt; SFE %26gt; approximate to 0.03(M-max/2.5 x 10(5) M-circle dot)(0.33), respectively. Moreover, the SFR of our model clouds follows closely the SFR-dense gas mass relation recently found by Lada et al. during the epoch when their instantaneous SFEs are comparable to those of the clouds considered by those authors. Collectively, a Monte Carlo integration of the model-predicted SFR(M) over a Galactic giant molecular cloud mass spectrum yields values for the total Galactic SFR that are within half an order of magnitude of the relation obtained by Gao %26 Solomon. Our results support the scenario that star-forming MCs may be in global gravitational collapse and that the low observed values of the SFR and SFE are a result of the interruption of each SF episode, caused primarily by the ionizing feedback from massive stars.

• 出版日期2014-10-1