Far and extreme UV radiation feedback in molecular clouds and its influence on the mass and size of star clusters

We study the formation of star clusters in molecular clouds by performing three-dimensional radiation hydrodynamics simulations with far-ultraviolet (FUV; 6 eV <= h nu <= 13.6 eV) and extreme ultraviolet (EUV; h nu >= 13.6 eV) radiative feedback. We find that the FUV feedback significantly suppresses the star formation in diffuse clouds with the initial surface densities of Sigma(cl) less than or similar to 50 M-circle dot pc(-2). In the cases of clouds with Sigma(cl) similar to 100 - 200 M-circle dot pc(-2), the EUV feedback plays a main role and decrease the star formation efficiencies less than 0.3. We show that thermal pressure from photodissociation regions or H II regions disrupts the clouds and makes the size of the star clusters larger. Consequently, the clouds with the mass M-cl less than or similar to 10(5) M-circle dot and the surface density Sigma(cl) less than or similar to 200 M-circle dot pc(-2) remain the star clusters with the stellar densities of similar to 100 M-circle dot pc(-3) that nicely match the observed open clusters in the Milky Way. If the molecular clouds are massive (M-cl greater than or similar to 10(5) M-circle dot) and compact (Sigma greater than or similar to 400 M-circle dot pc(-2)), the radiative feedback is not effective and they form massive dense cluster with the stellar densities of similar to 10(4) M-circle dot pc(-3) like observed globular clusters or young massive star clusters. Thus, we suggest that the radiative feedback and the initial conditions of molecular clouds are key factors inducing the variety of the observed star clusters.