exoALMA. XII. Weighing and Sizing exoALMA Disks with Rotation Curve Modelling

The exoALMA large program offers a unique opportunity to investigate the fundamental properties of protoplanetary disks, such as their masses and sizes, providing important insights into the mechanism responsible for the transport of angular momentum. In this work, we model the rotation curves of CO isotopologues ¹²CO and ¹³CO of 10 sources within the exoALMA sample, and we constrain the stellar mass, the disk mass, and the density scale radius through precise characterization of the pressure gradient and disk self-gravity. We obtain dynamical disk masses for our sample by measuring the self-gravitating contribution to the gravitational potential. We are able to parametrically describe their surface density, and all of them appear gravitationally stable. By combining dynamical disk masses with dust continuum emission data, we determine an averaged gas-to-dust ratio of approximately 400, not statistically consistent with the standard value of 100, assuming optically thin dust emission. In addition, the measurement of the dynamical scale radius allows for direct comparison with flux-based radii of gas and dust. This comparison suggests that substructures may influence the size of the dust disk and that CO depletion might reconcile our measurements with thermochemical models. Finally, with the stellar mass, disk mass, scale radius, and accretion rate, and assuming self-similar evolution of the surface density, we constrain the effective αS for these systems. We find a broad range of αS values ranging between 10⁻⁵ and 10⁻².