Revisiting the Galactic Winds in M82 I: the recent starburst and launch of outflow in simulations

TL;DR

This study uses hydrodynamic simulations with self-consistent star formation and feedback to analyze the launch and evolution of galactic outflows in M82, revealing the roles of supernova feedback, cool filaments, and gas return.

Contribution

It introduces a detailed simulation approach with sink particles to self-consistently model star formation and feedback in M82's outflow, improving upon simplified models.

Findings

Starburst lasts about 25 Myr with peak rates of 20-50 M_sun/yr.

Outflow develops in two stages, forming a kpc-scale wind after ~15 Myr.

Cool filaments survive feedback and are entrained in the outflow.

Abstract

We revisit the launch of the galactic outflow in M82 using hydrodynamic simulations. Employing a sink-particle module, we self-consistently resolve star formation and feedback, avoiding reliance on simplified models. We investigate the effects of stellar feedback mechanisms, gas return from star-forming clouds, and disk mass on the starburst and outflow. Our simulations generate a starburst lasting $\sim25$ Myr, peaking at 20-50 $\rm{M_{\odot},yr^{-1}}$, although the total stellar mass often exceeds M82's estimated value. The outflow develops in two stages: initially, continuous SNe form small bubbles that merge into a superbubble containing warm/hot gas and intermediate- to high-density cool filaments. After $\sim10$ Myr, the superbubble breaks out of the disk, and within $\sim15$ Myr a kpc-scale outflow forms. Cool filaments survive stellar feedback, become entrained in the wind, and stretch to hundreds of parsecs. Transport from the cool ISM is the dominant net contributor to the total mass of the cool phase in the outflow, whereas transfers from hotter phases, such as through condensation or precipitation, provide only a minor net contribution, likely offset by simultaneous transfer from the cool phase back to hotter phases. While the mass loading factor is comparable to M82, the cool gas outflow rate and velocity are lower, with velocities $\sim60\%$ below observed values; warm and hot gas are $\sim25\%$ slower. SN feedback is the primary driver, and gas return significantly influences the starburst and outflow, while other factors are secondary. Stronger clustered SN feedback is likely required to better match observations.