Modeling the Milky Way wind: Supernova-driven outflows accelerate HI clouds near the Galactic center

TL;DR

This study develops semi-analytical models of multiphase galactic outflows near the Milky Way's center, demonstrating that supernova-driven winds can accelerate HI clouds and reproduce observed cloud properties.

Contribution

The paper introduces physically motivated semi-analytical models of multiphase outflows including hot gas and cold clouds, validated with Bayesian inference against observations near the Galactic center.

Findings

Supernova-driven winds can explain observed HI cloud velocities and distribution.

Cold clouds are accelerated by hot winds through ram pressure and accretion.

Clouds lose over 70% of their mass by 2 kpc due to disruption.

Abstract

Multiwavelength observations, from radio to X-rays, have revealed the presence of multiphase high-velocity gas near the center of the Milky Way likely associated with powerful galactic outflows. This region offers a unique laboratory to study the physics of feedback and the nature of multiphase winds in detail. To this end, we have developed physically motivated semi-analytical models of a multiphase outflow consisting of a hot gas phase ($T \gg 10^6$ K) that embeds colder clouds ($T \sim 5000$ K). Our models include the gravitational potential of the Milky Way; the drag force exerted by the hot phase onto the cold clouds; and the exchange of mass, momentum, and energy between gas phases. Using Bayesian inference, we compared the predictions of our models with observations of a population of HI high-velocity clouds detected up to $\sim$1.5 kpc above the Galactic plane near the Galactic center. We find that a class of supernova-driven winds launched by star formation in the central molecular zone can successfully reproduce the observed velocities, spatial distribution, and masses of the clouds. In our two-phase models, the mass and energy loading factors of both phases are consistent with recent theoretical expectations. The cold clouds are accelerated by the hot wind via ram pressure drag and via accretion of high-velocity material, resulting from the turbulent mixing and subsequent cooling. However, this interaction also leads to gradual cloud disruption, with smaller clouds losing over 70\% of their initial mass by the time they reach $\sim$2 kpc.