Periodic Reporting for period 1 - MW-WINDS (The Milky Way system as a laboratory to understand the role of galactic winds in galaxy evolution)
Okres sprawozdawczy: 2022-09-01 do 2024-02-29
Massive stars and black holes in galaxies work together to launch gaseous winds at velocities that can reach several thousands of kilometres per second. These powerful winds are one of the most fascinating phenomena in our Universe and they are believed to play a key role in the evolution of a galaxy, as they slow down the formation of new stars and help galaxies interact and exchange material with their surrounding environment.
Determining how outflows work and pinning down the physical processes behind them are crucial questions in modern astrophysics. However, the physics driving the formation and evolution of galactic winds and their impact on the evolution of different host galaxies are still poorly constrained, although an increasing number of studies have been exploring these phenomena in the past years. Unfortunately, observations of winds in galaxies are often not good enough to constrain theoretical models, because they lack both the spatial resolution to distinguish the fine details and a complete view of these phenomena. In fact, matter in these winds is multi-phase, i.e. it can span several orders of magnitude in density and temperature, from a freezing temperature of a few Kelvin to staggering hot millions of Kelvin. To make progresses in the field, we need to gain a comprehensive understanding of these different gas phases and of how they interact with each other. This is challenging and requires a large number of detailed observations at different wavelengths of the electromagnetic spectrum with some of the most technological observing facilities available nowadays.
To understand these fascinating phenomena, MW-WINDS turns to our very own galaxy, the Milky Way, and its satellites, the Clouds, as the nearest cosmic laboratories in the Universe for studying galactic winds. Exploiting new data from forefront telescopes and advanced theoretical modelling, MW-WINDS is exploring the nature of matter living within winds with unprecedented accuracy. The final goal of this project is to reveal the origin and the physical mechanisms that drive these powerful events and to understand their role in shaping the galaxies that we see today.
Determining how outflows work and pinning down the physical processes behind them are crucial questions in modern astrophysics. However, the physics driving the formation and evolution of galactic winds and their impact on the evolution of different host galaxies are still poorly constrained, although an increasing number of studies have been exploring these phenomena in the past years. Unfortunately, observations of winds in galaxies are often not good enough to constrain theoretical models, because they lack both the spatial resolution to distinguish the fine details and a complete view of these phenomena. In fact, matter in these winds is multi-phase, i.e. it can span several orders of magnitude in density and temperature, from a freezing temperature of a few Kelvin to staggering hot millions of Kelvin. To make progresses in the field, we need to gain a comprehensive understanding of these different gas phases and of how they interact with each other. This is challenging and requires a large number of detailed observations at different wavelengths of the electromagnetic spectrum with some of the most technological observing facilities available nowadays.
To understand these fascinating phenomena, MW-WINDS turns to our very own galaxy, the Milky Way, and its satellites, the Clouds, as the nearest cosmic laboratories in the Universe for studying galactic winds. Exploiting new data from forefront telescopes and advanced theoretical modelling, MW-WINDS is exploring the nature of matter living within winds with unprecedented accuracy. The final goal of this project is to reveal the origin and the physical mechanisms that drive these powerful events and to understand their role in shaping the galaxies that we see today.
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). 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* (Di Teodoro 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.
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). 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* (Di Teodoro 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.
The discovery of multiphase, spatially-resolved, gas clouds outflowing from the Milky Way and from the Clouds opened new possibilities to increase our understanding of galactic winds and allowed us to develop novel methods to model how their physical properties evolve with time and distance from the galactic plane. By the end of the action, thanks to the synergy between models and observations, we expect to be able to pin down some of the most important physical processes at play in the launching and evolution of winds and to better understand their role in galaxy evolution.