Energy Budget in Supernovae-Driven HI Shells
Giant HI shells of several hundred parsecs and larger observed in nearby galaxies with a moderate inclination (i < 50°) are formed by multiple supernova explosions in stellar clusters. To estimate the total energy of these supernovae the relation obtained for the evolution of a single supernova in a homogeneous medium is commonly used. Here we study uncertainties encountered in estimating the total energy using the quantities measured in observations, i.e. radius and velocity of a shell, gas density before shock front of a shell. We analyze these quantities gained from the “synthetic observations” of the data obtained in the 3D simulations of the shell driven by multiple supernovae in a stratified interstellar medium. We show that the value of the total energy can be overestimated as well as underestimated in several times and more using the relation for a single supernova. We discuss how the estimate of the total energy depends on the properties of a gas (density, metallicity), scale height of a disk, number of supernovae and when this estimate is applicable for interpreting observations of H I shell in nearby galaxies.