The chemical inventory of the planet-hosting disk PDS 70

TL;DR

This study presents the first detailed chemical inventory of the PDS 70 disk, revealing complex molecular distributions and evidence of high C/O ratio gas accretion by planets, using ALMA observations.

Contribution

It provides the first comprehensive chemical inventory of the PDS 70 disk, including spatial distributions and abundance profiles of 12 molecules, and links these to planet formation processes.

Findings

12 molecular species detected, including CO isotopologues and formaldehyde.

Large central cavity in molecular lines indicates planet-induced gap.

Evidence of high C/O ratio gas accretion by planets.

Abstract

As host to two accreting planets, PDS 70 provides a unique opportunity to probe the chemical complexity of atmosphere-forming material. We present ALMA Band 6 observations of the PDS~70 disk and report the first chemical inventory of the system. With a spatial resolution of 0.4''-0.5'' ($\sim$50 au), 12 species are detected, including CO isotopologues and formaldehyde, small hydrocarbons, HCN and HCO+ isotopologues, and S-bearing molecules. SO and CH3OH are not detected. All lines show a large cavity at the center of the disk, indicative of the deep gap carved by the massive planets. The radial profiles of the line emission are compared to the (sub-)mm continuum and infrared scattered light intensity profiles. Different molecular transitions peak at different radii, revealing the complex interplay between density, temperature and chemistry in setting molecular abundances. Column densities and optical depth profiles are derived for all detected molecules, and upper limits obtained for the non detections. Excitation temperature is obtained for H2CO. Deuteration and nitrogen fractionation profiles from the hydro-cyanide lines show radially increasing fractionation levels. Comparison of the disk chemical inventory to grids of chemical models from the literature strongly suggests a disk molecular layer hosting a carbon to oxygen ratio C/O>1, thus providing for the first time compelling evidence of planets actively accreting high C/O ratio gas at present time.