Understanding JWST results: What thermochemical models tell us about the cold H2O content in disks
Abstract
JWST is allowing us to characterize the chemical composition of the inner, planet-forming regions of protoplanetary disks in more detail than even before. One particularly interesting finding is a prominent cold H2O reservoir seen in compact, drift-dominated disks that may trace ice sublimation near the H2O snowline, a site where planets may form. We investigate the origin of this cold emission using DALI thermochemical models. Interestingly, models with H2O abundances set by a chemical network do not show this cold emission inherently. Instead, an enhancement in abundance at the snow surface of 1-2 orders of magnitude is needed. We investigate what conditions or processes can produce such an enhancement in abundance, and thus how the presence or absence of this cold H2O reservoir can inform us of the conditions under which planets form in the inner regions of the disk.
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What can thermochemical models tell us about the cold H2O in disks? Marissa Vlasblom [email protected]||ESO New Frontiers - 12/03/25 || Image: M. Vlasblom
Water in disks Marissa Vlasblom [email protected]||Astrochemistry seminar 25/11/24 || ❖H2O is formed in the inner regions through gas-phase formation ❖Beyond the snowline, it is frozen out on the dust grains ❖Radial drift & sublimation can enhance inner disk H2O reservoir! Marissa Vlasblom [email protected]||ESO New Frontiers - 12/03/25 || Ref: Miotello et al. (2023)
Water in disks ❖Many ro-vibrational & rotational H2O lines seen with JWST-MIRI! Marissa Vlasblom [email protected]||Astrochemistry seminar 25/11/24 ||Marissa Vlasblom [email protected]||ESO New Frontiers - 12/03/25 || Ref: Temmink et al. (2024a,b) For more H2O as seen with MIRI: see Milou Temmink’s poster!
Water in disks ❖Dust And LInes (DALI) ➢1) Dust radiative transfer ➢2) Chemistry + thermal balance + excitation ➢3) Raytracing Marissa Vlasblom [email protected]||Astrochemistry seminar 25/11/24 ||Marissa Vlasblom [email protected]||ESO New Frontiers - 12/03/25 || H2O probed by JWST H2O probed by FIR/mm ❖JWST probes wide range of Eup ~1000 - 8000 K ❖Coldest H2O Eup <1000 K is probed by FIR/mm DALI: Bruderer et al. (2012, 2013)
Water in disks ❖Rotational H2O spectrum covers a wide range of excitation conditions ❖Can the lines tracing colder material tell us what is happening at the snowline? Marissa Vlasblom [email protected]||Astrochemistry seminar 25/11/24 ||Marissa Vlasblom [email protected]||Astrochemistry seminar 25/11/24 ||Marissa Vlasblom [email protected]||ESO New Frontiers - 12/03/25 || Ref: Banzatti et al. (2023)
Cold H2O emission ❖Lines around 23.8 micron are a good diagnostic for presence of cold H2O Marissa Vlasblom [email protected]||Astrochemistry seminar 25/11/24 || Warm emission only Needs a cold component! Marissa Vlasblom [email protected]||Astrochemistry seminar 25/11/24 ||Marissa Vlasblom [email protected] 1500 K 3000 K ||ESO New Frontiers - 12/03/25 || Ref: Banzatti et al. (2020, 2023, 2025); Romero-Mirza et al. (2024)
Cold H2O emission ❖Lines around 23.8 micron are a good diagnostic for presence of cold H2O ❖Strong cold H2O is mainly seen in compact disks Marissa Vlasblom [email protected]||Astrochemistry seminar 25/11/24 || ? ? dust gas Marissa Vlasblom [email protected]||Astrochemistry seminar 25/11/24 ||Marissa Vlasblom [email protected] Strong drift?Dust trapping? ❖Observations show diversity in these lines →what drives this? 1500 K 3000 K ||ESO New Frontiers - 12/03/25 || Ref: Banzatti et al. (2020, 2023, 2025); Romero-Mirza et al. (2024), Temmink et al. (subm.) →see Milou Temmink’s poster!
Thermochemical modeling ❖Can skip chemistry and parameterize abundances instead Marissa Vlasblom [email protected]||Astrochemistry seminar 25/11/24 ||Marissa Vlasblom [email protected]||Astrochemistry seminar 25/11/24 ||Marissa Vlasblom [email protected]||ESO New Frontiers - 12/03/25 || Ref: Vlasblom et al. (in prep.)
Thermochemical modeling ❖Can skip chemistry and parameterize abundances instead ❖Generate synthetic spectra with DALI models Marissa Vlasblom [email protected]||Astrochemistry seminar 25/11/24 ||Marissa Vlasblom [email protected]||Astrochemistry seminar 25/11/24 ||Marissa Vlasblom [email protected]||ESO New Frontiers - 12/03/25 || Chemistry → warm Param. abu. → cold ❖When determining the H2O abundance via the chemical network, the cold lines are not very prominent! Ref: Vlasblom et al. (in prep.)