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

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 kpcscale inhomogeneity, such as cavities, observed H I map of the LMC, is suppressed by frequent supernovae (average supernova rate for the whole disk is ∼ 0.001 yr−1). However the supernova explosions are necessary for the hot component (Tg > 10 6−7 K). Positionvelocity 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. In the quasi-stable phase, the volume filling factor of the hot, warm, cold components are ∼ 0.2,∼ 0.6, and ∼ 0.2, respectively. We compare the observations of H I and molecular gas of the LMC with the numerically obtained H I and CO brightness temperature distribution. The morphology and statistical properties of the numerical H I and CO maps are discussed. We find that the cloud mass spectrum of our models represent a power-law shape, but their slopes change between models with and without the stellar energy injection, and also the slope depends on the threshold brightness temperature of CO. Subject headings: ISM: structure, kinematics and dynamics — galaxies: structure — individual: LMC — method: numerical