Fasten Your Seatbelts: Constraining Ionization In A Turbulent Disk

Ionization plays a critical role in setting the chemical and dynamical processes within protoplanetary disks. Ions are responsible for the most rapid chemical processes which govern the formation of organics and water in the cold midplane of the disk, making ionization-driven chemistry central to the chemical evolution of any planets that may be forming within it. Ionization also has a significant impact on the transport of material throughout the disk via accretion and magneto-hydrodynamics (MHD). Sufficient ionization allows the gas to couple to magnetic field lines and in turn drives magneto-rotational instability (MRI). Regions in the midplane in which the disk is not MRI active (“dead zones”) are thought to be safe havens for planet formation. Therefore, constraining the ionization fraction throughout a disk is crucial for understanding both possible planet compositions and planet-forming capabilities. We present the first forward-modeled ionization map of the DM Tau protoplanetary disk, the first and only known disk with strong turbulence. Using ALMA observations of HCO+, DCO+, N2H+, and H2D+ combined with results from a grid of 2D chemical models, we attempt to constrain the ionization fraction throughout the disk. From these models, we speculate as to the physical and chemical mechanisms at play in the enigmatic DM Tau disk.