ASSESSING THE ROLE OF EXTERNAL PHOTOEVAPORATION OF PROTOPLANETARY DISCS IN NEARBY STAR-FORMING REGIONS

Characterising the physical processes driving protoplanetary disc evolution and the connection to the star-forming environment is essential to understanding planet formation and diversity. Most stars (and their discs) in the Galaxy form in massive clusters where the intense UV radiation emitted by OBA-type stars heats the outermost layers of protoplanetary discs, producing thermal winds that are launched from the disc surface. This causes outside-in disc depletion throughout external photoevaporation. In this thesis, I investigate how external photoevaporation shapes disc dynamics across a broad range of far-ultraviolet (FUV) radiation fields, focusing on nearby star-forming regions within 500 pc. Using numerical disc evolution models, I show that external photoevaporation can efficiently truncate discs and shorten their lifetime even under weak FUV fields (<1000 G0), where no direct observational evidence of ongoing photoevaporation (i.e., proplyds) is currently available. I demonstrate that external photoevaporation must be included alongside with viscous evolution to explain the gas sizes and masses of the Upper Scorpius discs investigated by the AGE-PRO ALMA Large Program. However, I discuss that obtaining model-independent evidence of external photoevaporation in moderately irradiated discs (1-100 G0), as in Upper Scorpius, remains challenging. I introduce a new method to evaluate the FUV flux at the position of stars that accounts for parallax uncertainty. Using the 2D geometry of a star-forming region, I derive the probability distribution of 3D separations from OBA-type stars. I apply this technique to provide an FUV flux map of the Orion region. Moreover, I investigate how the observed dust disc masses and stellar accretion luminosities depend on the FUV radiation field. This thesis emphasises the importance of accounting for external photoevaporation in typical planet-forming environments in the solar neighbourhood and provides new tools that will be fundamental for future observations.