Oral Presentation

Deuterium fractionation and ionization rate in proto-planetary disks by MAPS project

Author(s): Yoshihide Yamato (The University of Tokyo), Gianni Cataldi (The University of Tokyo/NAOJ), Yuri Aikawa (The University of Tokyo), ALMA MAPS Collaboration

Presenter: Yoshihide Yamato (The University of Tokyo)

Exploring the physical and chemical structures in proto-planetary disks is crucial to understand planet formation. In particular, deuterium fractionation (i.e., molecular D/H ratio) has been used to investigate the origin and thermal history of the Solar System material. As part of ALMA Large Program MAPS, we have detected N2D+ molecular line emission in four proto-planetary disks, two of which are the first detection in those disks. Together with the previous N2H+ observations, the high-resolution (~0.3") observations of N2D+ allowed us to estimate the radially-resolved distribution of N2D+/N2H+ ratio. High N2D+/N2H+ ratios (0.01 - 1) compared to the elemental D/H ratio (~10^{-5}) indicate efficient in situ deuterium fractionations in the disks. N2H+ and N2D+ can also be used as ionization tracers in disks. We compared the radial column density distributions of N2H+, N2D+, and HCO+ with template disk models. We found that the midplane ionization rate would be higher than 10^{-18} s^{-1} at least for disks with relatively high N2D+ column density, although source-specific modeling is desirable for confirmation.