Enhanced momentum feedback from clustered supernovae

Abstract

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 super-linearly with the number of SNe, resulting in a momentum per SN that 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 disk, 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 multi-dimensional instabilities or preexisting density variations, as a limiting factor in the buildup of momentum by clustered SNe, and suggest future numerical experiments to explore these effects.

A dynamical model for gas flows, star formation and nuclear winds in galactic centres

“…However, the simulations show that supernova momentum budget is not very sensitive to density, with fits to the simulation results giving scalings that vary from p SN ∝ n −0.06 (Gentry et al 2016) to p SN ∝ n −0.19 (Martizzi, Faucher-Giguère & Quataert 2015). Moreover, the clustering expected in high density regions can also enhance the momentum budget by a factor of several, pushing in the other direction (Gentry et al 2016). Thus our fiducial estimate should be reasonable even in the CMZ.…”

“…First, although we have included winds, radiation pressure, and supernovae, our choice of pSN implies that supernovae are by far the 2 One might worry that the momentum budget would be smaller at the n ∼ 10 4 cm −3 densities found in the CMZ than for the n ∼ 1 − 100 cm −3 densities found at larger radii, because supernova remnants would become radiative more quickly. However, the simulations show that supernova momentum budget is not very sensitive to density, with fits to the simulation results giving scalings that vary from p SN ∝ n −0.06 (Gentry et al 2016) to p SN ∝ n −0.19 (Martizzi, Faucher-Giguère & Quataert 2015). Moreover, the clustering expected in high density regions can also enhance the momentum budget by a factor of several, pushing in the other direction (Gentry et al 2016).…”

“…The starlight carries a momentum per unit stellar mass per unit time L(t)/c. For the supernovae, we adopt a momentum injection per supernova of pSN = 3 × 10 5 M km s −1 based on recent simulations (e.g., Martizzi, Faucher-Giguère & Quataert 2015;Kim & Ostriker 2015;Walch & Naab 2015;Gentry et al 2016), giving a supernova momentum injection rate ΓSN(t)pSN.…”

Winds of change: reionization by starburst galaxies

“…However, this problem may not arise for multiple bursts occurring in the same region (e.g. Gentry et al 2017). Moreover, Stanway, Eldridge & Becker (2016) argue that stellar population synthesis models that include binary stars may play an important role, because these binary stars have high luminosities in ionizing photons even at a time of order 100 Myr after the starburst (and after the massive stars have been able to open up channels through which photons can escape; see also Ma et al 2016).…”

The Physical Origin of Long Gas Depletion Times in Galaxies

“…The thermal energy and radial momentum injected by each supernova are calibrated against simulations of a SN remnant evolution in a nonuniform medium (Martizzi et al 2015), taking into account ambient gas density and with an additional boost of radial momentum by a fiducial factor of 5. We adopt such a boosting factor to compensate for the numerical loss of injected momentum and to account for the actual physical uncertainties of the radial momentum estimates (e.g., Gentry et al 2017). In addition to SNe type II feedback, during evolution, stellar particles return a fraction of their mass following the prescription of Leitner & Kravtsov (2011).…”