Protoplanetary disc population synthesis. I. Linking mass-dependent viscosity, star formation history, and environment to observations

Vollständiger Abstract

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Protoplanetary discs are the birthplaces of planets, and their lifetimes determine the time available for planet formation. Recent studies have highlighted the importance of stellar mass sampling when determining disc lifetimes through the observed fraction of stars with discs. Low-mass stars tend to host discs with average lifetimes exceeding 5 Myr, which provides sufficient time for planet formation via solid accretion. In addition, observations have shown a strong correlation between stellar (and substellar) mass and accretion rate, typically following the relation dot M ∝ M_⋆^2. The aim of this study was to identify the optimal parameters of a protoplanetary disc evolution model capable of reproducing both the observed disc fractions and the mass accretion rates in young stellar populations. We conducted a population synthesis study where disc evolution was modelled exploring different values of the viscosity parameter α as a function of stellar mass. The evolution of the discs was modelled through viscous accretion and photoevaporation (internal and external). Initial disc masses and radii were drawn from observationally motivated statistical distributions. We also introduced a stellar mass distribution and a star formation rate (SFR) in our population synthesis. Matching the observed disc fractions and accretion trends required that the α-viscosity parameter increases with stellar mass. External photoevaporation as well as a systematic underestimation of the gas disc masses due to dust evolution and hidden solids was required to reproduce the dot M -M_ ̊m d plane. Accounting for a time-dependent SFR enhanced accretion in young clusters and extended disc lifetimes in older ones. In addition, introducing a stellar mass cut-off reproduced the distance-dependent biases seen in cluster disc fractions. Our results indicate that both stellar and environmental dependencies are essential to explain the observed properties of protoplanetary discs. A stellar-mass–dependent viscosity is required to recover the relation, while external photoevaporation and extended star formation histories shape the distribution of accretion rates across different environments. These findings highlight the need for multi-faceted population synthesis models to connect disc evolution with planet formation pathways.