Dense Cloud Formation and Star Formation in a Barred Galaxy

Abstract

We investigate the properties of massive, dense clouds formed in a barred galaxy and their possible relation to star formation, performing a two-dimensional hydrodynamical simulation with the gravitational potential obtained from the 2Mass data from the barred spiral galaxy, M83. Since the environment for cloud formation and evolution in the bar region is expected to be different from that in the spiral arm region, barred galaxies are a good target to study the environmental effects on cloud formation and the subsequent star formation. Our simulation uses for an initial 80 Myr an isothermal flow of non-self gravitating gas in the barred potential, then including radiative cooling, heating and self-gravitation of the gas for the next 40 Myr, during which dense clumps are formed. We identify many cold, dense gas clumps for which the mass is more than $10^4M_{\odot}$ (a value corresponding to the molecular clouds) and study the physical properties of these clumps. The relation of the velocity dispersion of the identified clump's internal motion with the clump size is similar to that observed in the molecular clouds of our Galaxy. We find that the virial parameters for clumps in the bar region are larger than that in the spiral arm region. From our numerical results, we estimate star formation in the bar and spiral arm regions by applying the simple model of Krumholtz and McKee (2005). The mean relation between star formation rate and gas surface density agrees well with the observed Kennicutt-Schmidt relation. The SFE in the bar region is $\sim 60 %$ of the spiral arm region. This trend is consistent with observations of barred galaxies.