Formation of Stellar Bars in a Collapsing and Self‐gravitating Two‐Component Fluid

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Abstract
We numerically investigate the dynamical evolution of a rapidly collapsing and self-gravitating fluid composed of collisionless stars and collisional gas with a particular emphasis on the roles of star formation in the formation of a stellar bar. We adopt idealized and generalized initial conditions of the collapsing two-component fluid and rather simplified models for star formation and investigate the dynamical roles of gas consumption by star formation in stellar bar formation. We found that the rapidity of gas consumption by star formation predominantly determines whether or not a stellar bar forms after the collapsing two-component fluid reaches virial equilibrium: A stellar bar is more likely to form in a two-component fluid with rapid star formation, whereas inhomogeneous structures (e.g., a few clumps) are more likely to form in a fluid with gradual star formation. This is principally because the growth of gaseous clumps, which is a key determinant for suppressing the growth of global bar instability, is inhibited more significantly by gas consumption in the two-component fluid with more rapid star formation. Furthermore, we found that this particularly important role of gas consumption by star formation does not depend strongly on the initial virial ratio and initial fraction of gas mass in the two-component fluid. These results demonstrate that the rapidity of gas consumption by star formation during collapse is one of crucial parameters for the formation of a stellar bar in collapsing and self-gravitating two-component fluid. Although our numerical models are rather idealized and less realistic, these results provide a clue to the understanding of stellar bar formation in forming disk galaxies.