http://arxiv.org/abs/1802.06860
While the evolution of superbubbles driven by clustered supernovae (SNe) has been studied by numerous authors, the resulting radial momentum yield is uncertain by as much as an order of magnitude depending on the computational methods and the assumed properties of the surrounding interstellar medium (ISM). In this work, we study the origin of these discrepancies, and seek to determine the correct momentum budget. We carry out 3D hydrodynamic and magnetohydrodynamic simulations of clustered supernova explosions, using a Lagrangian method and checking for convergence as we increase the resolution. We find that the terminal momentum of a shell driven by clustered supernovae is dictated almost entirely by the rate of mixing across the contact discontinuity between the hot and cold phases, and that this mixing rate is dominated by numerical diffusion even at the highest resolution we can achieve, 0.03 $M_\odot$. Magnetic fields also reduce the mixing rate, so that MHD simulations produce higher momentum yields than HD ones at equal resolution. As a result, we obtain only a lower limit on the momentum yield from clustered supernovae. Combining this with our previous 1D results, which provide an upper limit because they allow almost no mixing across the contact discontinuity, we conclude that the momentum yield per SN from clustered SNe is bounded between $2\times 10^5$ and $3\times 10^6$ $M_\odot$ km s$^{-1}$. We urge that published claims to provide a converged value for this quantity, which are based on simulations with substantially higher rates of numerical diffusion than ours, be treated with caution.
E. Gentry, M. Krumholz, P. Madau, et. al.
Wed, 21 Feb 18
29/58
Comments: 9 page, 7 figures, submitted to MNRAS