Cloud Formation by Supernova Implosion

Abstract

The deposition of energy and momentum by supernova explosions has been subject to numerous studies in the past few decades. However, while there has been some work that focused on the transition from the adiabatic to the radiative stage of a supernova remnant (SNR), the late radiative stage and merging with the interstellar medium (ISM) have received little attention. Here, we use three-dimensional, hydrodynamic simulations, focusing on the evolution of SNRs during the radiative phase, considering a wide range of physical explosion parameters ($n_{\text{H, ISM}} \in \left[0.1, 100\right] \text{cm}^{-3}$ and $E_{\text{SN}} \in \left[1, 14\right]\times 10^{51} \text{erg}$). We find that the radiative phase can be subdivided in four stages: A pressure driven snowplow phase during which the hot overpressurized bubble gas is evacuated and pushed into the cold shell, a momentum conserving snowplow phase which is accompanied by a broadening of the shell, an implosion phase where cold material from the back of the shell is flooding the central vacuum and a final cloud phase, during which the imploding gas is settling as a central, compact overdensity. The launching timescale for the implosion ranges from a few 100 kyr to a few Myr, while the cloud formation timescale ranges from a few to about 10 Myr. The highly chemically enriched clouds can become massive ($M_{\text{cl}} \sim 10^3 - 10^4 \, \text{M}_{\odot}$) and self-gravitating within a few Myr after their formation, providing an attractive, novel pathway for supernova induced star and planet formation in the ISM.