Enhanced momentum feedback from clustered supernovae

Young stars typically form in star clusters, so the supernovae (SNe) they produce are clustered in space and time. This clustering of SNe may alter the momentum per SN deposited in the interstellar medium (ISM) by affecting the local ISM density, which in turn affects the cooling rate. We study the effect of multiple SNe using idealized 1D hydrodynamic simulations which explore a large parameter space of the number of SNe, and the background gas density and metallicity. The results are provided as a table and an analytic fitting formula. We find that for clusters with up to ∼100 SNe, the asymptotic momentum scales superlinearly with the number of SNe, resulting in a momentum per SN which can be an order of magnitude larger than for a single SN, with a maximum efficiency for clusters with 10–100 SNe. We argue that additional physical processes not included in our simulations – self-gravity, breakout from a galactic disc, and galactic shear – can slightly reduce the momentum enhancement from clustering, but the average momentum per SN still remains a factor of 4 larger than the isolated SN value when averaged over a realistic cluster mass function for a star-forming galaxy. We conclude with a discussion of the possible role of mixing between hot and cold gas, induced by multidimensional instabilities or pre-existing density variations, as a limiting factor in the build-up of momentum by clustered SNe, and suggest future numerical experiments to explore these effects. Key words: hydrodynamics – ISM: bubbles – ISM: supernova remnants.This work was supported by the NSF through grants AST-1405962 (ESG, MRK, and AD), AST-1229745 (PM), and DGE 1339067 (ESG), by the Australian Research Council through grant ARC DP160100695 (MRK) and by NASA through grant NNX12AF87G (PM). AD’s work is also supported by the grants ISF 124/12, I-CORE Programme of the PBC/ISF 1829/12, and BSF 2014-273. MRK thanks the Simons Foundation, which contributed to this work through its support for the Simons Symposium ‘Galactic Superwinds: Beyond Phenomenology’. PM thanks the Prefecture of the Ile-de-France Re- ´ gion for the award of a Blaise Pascal International Research Chair, managed by the Fondation de l’Ecole Normale Superieure