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Context. The physical mechanisms that regulate the collapse of high-mass parsec-scale clumps and allow them to form clusters of new stars, including high-mass stars, represent a crucial aspect of star formation. Aims. To investigate these mechanisms, we developed the Rosetta Stone project: an end-to-end (simulations ⇔ observations) framework that is based on the systematic production of realistic synthetic observations of clump fragmentation and their subsequent comparison with real data. Methods. In this work, we compare ALMA 1.3 mm continuum dust emission observations from the Star formation in QUiescent And Luminous Objects (SQUALO) survey with a new set of 24 radiative magnetohydrodynamical (RMHD) simulations of high-mass clump fragmentation, post-processed using the CASA software to mimic the observing strategy of SQUALO (combining ACA and 12 m array). The simulations were initialized combining typical values of clump mass (500 and 1000 M_⊙) and radius (∼0.4 pc) with two levels of turbulence (Mach number,M, of 7 and 10) and three levels of magnetization (normalized mass-to-magnetic-flux ratio, µ, of ∼3, 10, and 100). Following the clump evolution over time with two initial random seeds projected along three orthogonal directions, we produced a collection of 732 synthetic fields. On each field, we performed source extraction and photometry using theHypersoftware, as in the SQUALO project, to quantitatively characterize how the initial conditions of the clump and the environment affect the observed fragmentation properties. Results. The synthetic observations of clump fragmentation at ∼7000 AU resolution revealed between 2 and 14 fragments per field, indicating a complex fragmentation process. Among the initial conditions of the simulations, magnetic fields have the largest impact on the fragment multiplicity at these scales. In advanced stages of clump evolution, a lower number of fragments is preferentially associated with magnetized clumps. The clump magnetization might also affect the clustering of fragments, favoring more tightly bound distributions when the magnetic field is stronger. Fragments identified at ∼7000 AU correspond to individual or multiple sink particles in ∼75% of the cases. This result suggests that not all identified fragments are actively forming stars. Both sink particles and fragments accrete mass throughout the whole clump evolution. This evidence favors a scenario in which fragments are not isolated from the environment and is thus consistent with results from the SQUALO survey. Conclusions. Our study demonstrates the importance of synthetic observations in interpreting results from interferometric observations. 

Abstract The architecture of planetary systems depends on the evolution of the disks in which they form. In this work, we develop a population synthesis approach to interpret the Atacama Large Millimeter/submillimeter Array survey of Gas Evolution of PROtoplanetary Disks (AGE-PRO) measurements of disk gas mass and size considering two scenarios: turbulence-driven evolution with photoevaporative winds and MHD wind-driven evolution. A systematic method is proposed to constrain the distribution of disk parameters from the disk fractions, accretion rates, disk gas masses, and CO gas sizes. We find that turbulence-driven accretion with initially compact disks (R₀ ≃ 5–20 au), low mass-loss rates, and relatively long viscous timescales (t_ν,0 ≃ 0.4–3 Myr orα_SS ≃ 2–4 × 10⁻⁴) can reproduce the disk fractions and gas sizes. However, the distribution of apparent disk lifetimes defined as the $M_D/{\dot{M}}_{*}$ratio is severely overestimated by turbulence-driven models. On the other hand, MHD wind-driven accretion can reproduce the bulk properties of disk populations from Ophiuchus to Upper Scorpius assuming compact disks with an initial magnetization of aboutβ ≃ 10⁵(α_DW ≃ 0.5–1 × 10⁻³) and a magnetic field that declines with time. More studies are needed to confirm the low masses found by AGE-PRO, notably for compact disks that question turbulence-driven accretion. The constrained synthetic disk populations can now be used for realistic planet population models to interpret the properties of planetary systems on a statistical basis. 

Recent years have seen a surge of interest in the community studying the effect of ultraviolet radiation environment, predominantly set by OB stars, on protoplanetary disc evolution and planet formation. This is important because a significant fraction of planetary systems, potentially including our own, formed in close proximity to OB stars. This is a rapidly developing field, with a broad range of observations across many regions recently obtained or recently scheduled. In this paper, stimulated by a series of workshops on the topic, we take stock of the current and upcoming observations. We discuss how the community can build on this recent success with future observations to make progress in answering the big questions of the field, with the broad goal of disentangling how external photoevaporation contributes to shaping the observed (exo)planet population. Both existing and future instruments offer numerous opportunities to make progress towards this goal.