Class 0/I disk sizes in Orion

Envelope-embedded Class 0 and I protostars represent the earliest stage of protoplanetary disk evolution, setting the initial conditions for subsequent disk growth and planet formation. Despite their importance, the bulk properties of these disks remain poorly constrained statistically, primarily because the surrounding envelope emission contaminates interferometric observations.

We present an analysis of high angular resolution ALMA Band 7 archival data from the Orion VANDAM survey. To robustly separate disk and envelope contributions, we perform visibility-plane fitting using a two-component model: a Gaussian disk and a Plummer-sphere envelope profile. This approach allows us to reliably constrain disk radii for a sample of 120 Class 0 and Class I sources in Orion.

We find that Class 0 disks are systematically smaller than Class I disks, with median radii of 40 AU and 50 AU, respectively. This confirms that disks are born small and grow over time, consistent with magnetic braking playing a significant role in regulating angular momentum during the earliest collapse phase.

We further analyze complementary VLA 9 mm data and investigate the multiwavelength radius–luminosity scaling relation for both classes, comparing it with that established for more evolved Class II disks, and to constrain dust grain properties and opacity in the youngest embedded disks. We additionally compare our observed disk size distributions with synthetic disk populations from numerical simulations spanning a range of physical conditions, in order to assess which formation scenarios are most consistent with the data. Together, these results place strong observational constraints on the initial conditions of disk evolution and planet formation.