MW-WINDS is exploiting the proximity of our Galaxy and its satellites to obtain a detailed view of the matter in local winds. The Milky Way is known to host a large-scale biconical outflow in its central regions, driven either by the intense star formation or by a recent explosion from our super-massive black hole, Sagittarius A*. The Clouds, two dwarf galaxies orbiting around our Galaxy, are forming stars at a high pace stimulated by the strong tidal interactions with the Milky Way, and they are expected to easily launch winds.
This ERC project has been collecting some of the best observational data available nowadays of the multi-phase gas in these local outflows. Data have been taken from telescopes that mostly operates in the radio and millimiter/sub-millimiter wavelengths of the electromagnetic radiation, including but not limited to the Greenbank Telescope (GBT), the Australian SKA Pathfinder (ASKAP), the MeerKAT telescope and the Atacama Pathfinder Experiment (APEX). Thanks to the proximity of these winds, it was possible to observe outflowing gas clouds and to resolve their structure on scales of less than a parsec.
In the first part of the project, a consistent amount of work has been dedicated to the acquisition and reduction of all these datasets and to make them ready for full science exploitation. These data are allowing us to study two of the most important phases in the outflows: the molecular gas phase, with typical temperatures of less than 100 Kelvin, and the neutral atomic phase with temperatures up to 10000 Kelvin. These are the densest and coldest phases in the winds and they are expected to have a strong impact on the star formation history of a galaxy, because the kind of gas from which stars are assembled is directly removed from the galaxy itself. The new data is revealing some key physical properties of this gas, including its internal structure (i.e. temperature, density, pressure, mass), its morphology and its kinematics (i.e. velocity, acceleration, level of turbulence). For example, our early results show that significant quantities of cold molecular and neutral gas clouds are being driven out of the star-forming disk and accelerated to a maximum velocity of 400 km/s by the pressure exerted by the hotter, fast moving outflowing gas (Di Teodoro et al. 2020, Heyer et al. 2025). While entrained in this wind, the cold gas clouds get shredded and destroyed on timescales of a few million years because of the interaction with the hotter components (Noon et al., 2023; Gerrard et al. 2024). Our data allowed us to estimate that our Galaxy is expelling at least 0.2 solar masses of cold gas every year in this process.
Beside deriving these important observational properties, MW-WINDS is also developing new theoretical models that will be used as a benchmark for interpreting the data. In particular, we are currently focusing on the Galactic Center environment and developing both dynamical models of the outflowing cloud orbits and a suite of simulations of the inner regions of our Galaxy. Our dynamical models are suggesting that the main driving mechanism for the launching of cold clouds in the Galactic Center is the star formation, while they seem to rule out an acceleration mechanism driven by a past active galactic nucleus (AGN) activity from Sagittarius A* (Afruni et al, in prep.). In parallel to the dynamical models, we are preparing a new suite of 3D magnetohydrodynamical simulations to study how different physical ingredients (e.g. radiative cooling, thermal conduction, magnetic fields, cosmic rays) are impacting the evolution of local outflows.
