"Is There a Relationship Between the Cosmic-Ray Ionization Rate and Protostellar Disk Radius?"

Abstract:

Observations of dense protostellar cores indicate high levels of magnetization, strong enough in MHD simulations to suppress the formation of rotationally-supported protostellar disks. However, large disks continue to be detected around a growing number of young protostars, suggesting that additional physical mechanisms are needed to enable disk formation in magnetized environments. Non-ideal MHD effects provide one possible solution, but their observational signatures are difficult to detect and quantify directly. Since cosmic-ray ionization influences the ionization fraction, and therefore the efficiency of non-ideal MHD effects, measurements of the cosmic-ray ionization rate and ionization fraction can provide indirect constraints on the role of non-ideal MHD during disk formation. Here, we present JCMT observations of DCO+ and H13CO+ toward 16 dense protostellar cores with well-constrained disk radii from the eDisk ALMA Large Program. Using these observations, we estimate the cosmic-ray ionization rate and ionization fraction in order to statistically assess the importance of non-ideal MHD in the formation of protostellar disks.