Simulating Observations of Ices in Protoplanetary Disks

TL;DR

This paper develops models to predict how upcoming JWST observations can detect and analyze ices in protoplanetary disks, providing insights into their composition, distribution, and initial chemical conditions.

Contribution

The study introduces a comprehensive modeling framework combining chemical evolution and radiative transfer to interpret future JWST observations of disk ices.

Findings

IR features of H2O, CO2, and CH3OH are observable in inclined disks.

CH3OH ice is a diagnostic of initial chemical conditions due to its low abundance in reset models.

CO2 ice features vary with disk evolution, decreasing in inheritance models and increasing in reset models.

Abstract

Ices are an important constituent of protoplanetary disks. New observational facilities, notably the James Webb Space Telescope (JWST), will greatly enhance our view of disk ices by measuring their infrared spectral features. We present a suite of models to complement these upcoming observations. Our models use a kinetics-based gas-grain chemical evolution code to simulate the distribution of ices in a disk, followed by a radiative transfer code using a subset of key ice species to simulate the observations. We present models reflecting both molecular inheritance and chemical reset initial conditions. We find that near-to-mid-IR absorption features of H$_2$O, CO$_2$, and CH$_3$OH are readily observable in disk-integrated spectra of highly inclined disks while CO, NH$_3$, and CH$_4$ ice do not show prominent features. CH$_3$OH ice has low abundance and is not observable in the reset model, making this species an excellent diagnostic of initial chemical conditions. CO$_2$ ice features exhibit the greatest change over disk lifetime, decreasing and increasing for the inheritance and reset models, respectively. Spatially resolved spectra of edge-on disks, possible with JWST's integral field unit observing modes, are ideal for constraining the vertical distribution of ices and may be able to isolate features from ices closer to the midplane (e.g., CO) given sufficient sensitivity. Spatially-resolved spectra of face-on disks can trace scattered-light features from H$_2$O, CO$_2$, and CH$_3$OH, plus CO and CH$_4$ from the outermost regions. We additionally simulate far-IR H$_2$O ice emission features and find they are strongest for disks viewed face-on.