The demographics of protoplanetary disks: from Lupus to Orion

The work presented in this thesis is based on ALMA surveys of protoplanetary disks in three star-forming regions: Lupus, OMC-2, and NGC 2024. The motivation for this thesis is to study the evolution of protoplanetary disks from the population level.The first two chapters focus on the Lupus clouds, a low-mass star-forming region. It has been the subject of a large survey with ALMA, targeting bright gas lines and the emission from millimeter-sized grains. This allows us to answer important questions on disk evolution: how common are >200 AU-sized disks with continuum substructure, and how are these substructures formed? Do compact disks observed in the continuum also correspond to compact gas disks?The chapters focusing on Orion deal with the impact of massive stars on disks. OMC-2 provides a view of a population of disks that are formed in a massive cloud, but isolated from the radiation of massive stars. They link disks that do form near these massive stars to those in low-mass YSOs. NGC 2024 also hosts massive stars, and is the youngest region surveyed; the presence of multiple populations of young stars has been suggested. ALMA allows us to independently test the complexity of this environment.Stars and planetary system