Formation of Cavities, Filaments, and Clumps by the Non-linear Development of Thermal and Gravitational Instabilities in the Interstellar Medium under Stellar Feedback

Abstract

Based on our high resolution, two-dimensional hydrodynamical simulations, we propose that large cavities may be formed by the nonlinear development of the combined thermal and gravitational instabilities, without need for stellar energy injection in a galaxy modeling the Large Magellanic Clouds (LMC). Our numerical model of the star formation allows us to follow the evolution of the blastwaves due to supernovae in the inhomogeous, multi-phase, and turbulent-like media self-consistently. Formation of kpc-scale inhomogeneity, such as cavities, observed HI map of the LMC, is suppressed by frequent supernovae (average supernova rate for the whole disk is ~0.001/yr). However the supernova explosions are necessary for the hot component (T_g > 10^{6-7} K). Position-velocity maps show that kpc-scale shells/arcs formed through the nonlinear evolution in a model without stellar energy feedback has similar kinematics to explosional phenomena, such as supernovae. We also find that dense clumps and filamentary structure are formed due to a natural consequence of the non-linear evolution of the multi-phage ISM. Although the ISM in a small scale looks turbulent-like and transient, the global structure of the ISM is quasi-stable. We compare the observations of HI and molecular gas of the LMC with the numerically obtained HI and CO map. The morphology and statistical properties of the numerical HI and CO maps are discussed.