No Impact of Core-scale Magnetic Field, Turbulence, or Velocity Gradient on Sizes of Protostellar Disks in Orion A

Abstract

We compared the sizes and fluxes of a sample of protostellar disks in Orion A measured with the Atacama Large Millimeter/submillimeter Array 0.87 mm continuum data from the VLA/ALMA Nascent Disk and Multiplicity survey with the physical properties of their ambient environments on the core scale of 0.6 pc estimated with the Green Bank Ammonia Survey data and the legacy catalog datasets of the polarimeter for the Submillimeter Common-User Bolometer Array. We did not find any significant dependence of the disk radii and continuum fluxes on a single parameter on the core scale, such as nonthermal line width, magnetic field orientation and strength, or magnitude and orientation of the velocity gradient. Among these parameters, we only found a positive correlation between the magnitude of the velocity gradient and the nonthermal line width. Thus, the observed velocity gradients are more likely related to turbulent motion but not large-scale rotation. Our results of no clear dependence of the disk radii on these parameters are more consistent with the expectation from nonideal MHD simulations of disk formation in collapsing cores, where the disk size is self-regulated by magnetic braking and diffusion, compared to other simulations that only include turbulence and/or a magnetic field misaligned with the rotational axis. Therefore, our results could hint that the nonideal MHD effects play a more important role in the disk formation. Nevertheless, we cannot exclude the influences on the observed disk size distribution by dynamical interaction in a stellar cluster or amounts of angular momentum on the core scale, which cannot be probed with the current data.