Momentum Injection by Supernovae in the Interstellar Medium

Supernova (SN) explosions deposit prodigious energy and momentum in their en-vironments, with the former regulating multiphase thermal structure and the latter regulating turbulence and star formation rates in the interstellar medium (ISM). In contrast to the extensive efforts developing spherical models for SN remnant (SNR) evolution, systematic studies quantifying the impact of SNe in more realistic inhomoge-neous ISM conditions have been lacking. Using three-dimensional hydrodynamic sim-ulations with optically-thin radiative cooling, we investigate the dependence of radial momentum injection on both physical conditions (considering a range of mean density n0 = 0.1−100 cm−3) and numerical parameters. Our inhomogeneous simulations adopt two-phase background states that result from thermal instability in atomic gas. Al-though the SNR morphology becomes highly complex for inhomogeneous backgrounds, the radial momentum injection is remarkably insensitive to environmental details. For our two-phase simulations, the final momentum produced by a single SN is given by 2.8 × 105 M km s−1n−0.170. This is only 5 % less than the momentum injection for a homogeneous environment with the same mean density, and only 30 % greater than the momentum at the time of shell formation. The maximum mass in hot gas is quite insensitive to environmental inhomogeneity. Initial experiments with multiple spatially-correlated SNe show a similar momentum per event to single-SN cases. We also present a full numerical parameter study to assess convergence requirements. For convergence in the momentum and other quantities, we find that the numerical resolution ∆ and the initial size of the SNR rinit must satisfy ∆, rinit rsf/3, where the shell formation radius is given by rsf = 30 pc n −0.46 0 for two-phase models (or 30 % smaller for a homogeneous medium). Subject headings: methods:numerical – supernovae: general – ISM: supernova remnants – ISM: kinematics and dynamics 1.