The JDISC Survey: Linking the Physics and Chemistry of Inner and Outer Protoplanetary Disk Zones

Abstract

Mid-infrared spectroscopy of protoplanetary disks provides a chemical inventory of gas within a few astronomical unit, where planets are readily detected around older stars. With the James Webb Space Telescope (JWST) Disk Infrared Spectral Chemistry Survey, we explore demographic trends among 31 disks observed with MIRI (MRS) and with previous Atacama Large Millimeter/submillimeter Array millimeter continuum imaging at high angular resolution (5–10 au). With these signal-to-noise ratio of ∼200–450 spectra, we report emission from H₂O, OH, CO, C₂H₂, HCN, CO₂, [Ne ii], [Ne iii], and [Ar ii]. Emission from H₂O, OH, and CO is nearly ubiquitous for low-mass stars, and detection rates of all molecules are higher than for similar disks observed with Spitzer-IRS. Slab model fits to the molecular emission lines demonstrate that emission from C₂H₂, HCN, and possibly CO₂ is optically thin; thus since column densities and emitting radii are degenerate, observations are actually sensitive to the total molecular mass. C₂H₂ and HCN emission also typically originate in a hotter region (920⁺⁷⁰₋₁₃₀,  820⁺⁷⁰₋₁₃₀ K, respectively) than CO₂ (600⁺²⁰⁰₋₁₆₀ K). The HCN to cold H₂O luminosity ratios are generally smaller in smooth disks, consistent with more efficient water delivery via icy pebbles in the absence of large dust substructures. The molecular emission-line luminosities are also correlated with mass accretion rates and infrared spectral indices, similar to trends reported from Spitzer-IRS surveys. This work demonstrates the power of combining multiwavelength observations to explore inner disk chemistry as a function of outer disk and stellar properties, which will continue to grow as the sample of observed Class II systems expands in the coming JWST observation cycles.

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