Mapping the Ionization Environments of Planet Forming Disks

Deryl Eden Long

Placing accurate constraints on disk ionization is critical for understanding the chemistry and physics at play within planet forming disks. Ions drive important chemical and physical processes, including the formation of organics and water in the cold midplane of the disk as well as the overall evolution and dispersal of the gas disk. Despite its importance, there are relatively few constraints on the nature of disk ionization in observed protoplanetary disks, and for those with constraints, the overall ionization is typically low. We present results of a 2D study of ionization in a diverse sample of sources. We use ALMA observations of HCO+, DCO+, N2H+, and H2D+ combined with a grid of 2D chemical models with varying cosmic-ray ionization rates and stellar X-ray spectra to constrain the disks’ ionization fractions. We explore commonalities and differences across the sample and discuss the relationships between ionization and other disk properties. Such studies will be invaluable as the upcoming ALMA DECO Large Program will yield new observations of the cold ionization tracer N2H+ in 80 disks, providing a broad view of ionization across a large sample of disks.