Revisiting the Galactic Winds in M82 II: Development of Multiphase Outflows in Simulations

Abstract

We performed a suit of three-dimensional hydrodynamical simulations with a resolution of $\sim10$ parsecs to investigate the development of multiphase galactic wind in M82. The star formation and related feedback processes are solved self-consistently using a sink particle method, rather than relying on various assumptions that were used in previous studies. Our simulations produce a starburst event lasting around 25 Myr, which has a total stellar mass of 1.62 - 3.34 $\times 10^8\, \rm{M_{\odot}}$, consistent with observational estimates. The total injected supernova energy is between $1.14\times 10^{57}$ and $2.4\times 10^{57} \rm{erg}$. Supernova (SN) feedback heats portions of the cool gas in the central disc to warm and hot phases, and then drives the gas in all three phases out, eventually forming multiphase outflows. These outflows can replicate key properties of the winds observed in M82, such as morphology, mass outflow rate, and X-ray emission flux, provided the gas return from star-forming clumps to the interstellar medium is implemented appropriately. The maximum mass outflow rate of all gas (hot) is about 6-12 (2-3)$\rm{M_{\odot}/yr}$ at $r\sim4.0\,$ kpc, corresponding to a mass loading factor of 2-4. However, the outflow velocities in our simulations are slower than observational estimates by $\sim 20\%-60\%$. The gas return process significantly influences the outflow properties, while the initial gas distribution in the nuclear region has a moderate effect. However, our results face some challenges in achieving convergence as the resolution increases. We discuss potential improvements to address these issues in future work.