The evolution and physical appearance of galaxies are governed by a complex cycle of matter and energy. Global dynamical agents such as collisions between galaxies, or the spiral arms and bars we observe within galaxies, guide the process of stellar birth on small scales. Viceversa, the local energy and momentum input from newly born stars drives turbulence and influences the large-scale dynamics of the interstellar medium (ISM). Stellar feedback (radiation, winds, supernova explosions) determines the chemical and thermal state of the ISM, which in turn affects subsequent star formation via a hierarchy of interwoven feedback loops. In this cascade of scales, we can identify several key object classes. These are giant molecular clouds, which constitute the dense phase of the ISM, star proto-clusters that form in their interior, dense cores on yet smaller scales, that collapse under their own gravitational weight to build up accretion disks, in which individual stars and their planetary systems form. Understanding our Galactic ecosystem through this hierarchy of structures is a cornerstone for our knowledge of cosmic evolution and is the primary research goal of the ECOGAL project. 

ECOGAL is an ambitious, wide ranging project, founded by an ERC-Synergy Grant (2020-2026) PI: Sergio Molinari (INAF-IAPS), Patrick Hennebelle  (CEA-Saclay),  Ralf Klessen (Heidelberg University) and Leonardo Testi (Università di Bologna), aimed at produce a comprehensive view of the formation of structures in the Milky Way at all the scales from the protoplanety disks to spiral arms, linking together all the involved agents, usually studied separately.

 A wealth of observational data is now available to study molecular clouds and their properties such as their mass, velocity dispersion, and chemical make-up. Still, it is not clear how long these clouds live, when and how they disperse, and what fraction of their mass is converted into stars. Numerical simulations of full galactic disks generated in the past decade still suffer from insufficient spatial resolution or physical processes considered. With ECOGAL we will go beyond the current state-of-the-art by combining novel zoom-in techniques with global disk simulations. The initial and boundary conditions are taken from the best datasets for the Milky Way, to produce models as realistic as possible. Our goal is to build a large database of simulated molecular clouds in different Galactic environments with very high resolution and unprecedented physical fidelity, and to produce synthetic observations for one-to-one comparison with astronomical data. 

Most stars form in clusters, but how these get assembled in the deep interior of molecular clouds is still not well understood.  From previous studies we have characterized the basic physical properties of proto-cluster clumps, but due to the lack of spatial resolution our current knowledge of their internal spatial structure, and hence of the details of their fragmentation processes into dense cores, still remains limited. ALMA is dramatically improving this situation, as it allows us to study this critical phase of evolution with about 100 times higher resolution than previously possible on large samples of dense clumps. On the theory side, analytic studies and numerical simulations indicate that the proto-cluster gas is heavily influenced by initial conditions and by the dynamics of the parental cloud. However, there is no systematic investigation of the combined role of the proto-cluster environment and of the impact of all feedback processes. By zooming in from molecular cloud simulations including all forms of feedback, we will for the first time follow the entire formation process of stellar clusters self-consistently down to the scale of the dense cores. 

On the next level of the hierarchy of scales, planet-forming disks are the immediate progenitors of planetary systems and determine their characteristic properties. Disks form early in the star and planet formation process, and last for several million years. Getting a complete history of the temporal evolution of disks and a comprehensive overview of their key parameters to understand which physical process controls the formation and size of disks is a critical challenge: is it the magnetic field, or the angular momentum distribution of the parental core, or maybe some other mechanism? We will address these problems with new observational surveys of disks in massive clouds that also probe properties of the magnetic field. On the theory side, most studies so far have considered disks in isolation. However, we now know that the environment plays a key role. Taking advantage of the cluster simulations in ECOGAL, we will pursue a suite of deep zoom-in calculations with the appropriate environmental conditions that will result in a complete population of accretion disks together with their time evolution. The comparison with our observational survey data, allows us to predict the distribution of planet-forming disks in the Galaxy. We will use the disk calculations as input for ‘effective models’ of planet formation, building up a synthetic population of planets for the model star clusters.
In summary, in a concerted multi-faceted approach that combines a wide range of complementary expertise, we will use state-of-the-art astronomical observations together with high-resolution computer simulations and innovative analysis tools, to attack four scientific cornerstone topics: 

1  characterize the main drivers of ISM dynamics, 

2  assess how the different phases of the ISM form and evolve, 

3  identify the processes that govern the build-up of stars in dense clouds, 

4  determine how the star-forming environment influences the properties of protoplanetary disks and their ability to build planets. 

This will result in the fundamental breakthrough of providing a unifying model, with predictive power, of the Milky Way as a star and planet formation engine by linking observable data and the expected statistical distributions of key physical parameters.