H2O photodissociation timescale and turbulent diffusion mixing timescale of the fiducial model using the chemical network. The 1, 10 and 100 year timescale contours are indicated in white in both panels. The dark blue contours in both panels indicates the 10−5 , 10−6 , and 10−8 H2O abundance contours of the fiducial chemistry model (see also top left panel of Fig. 1). The light blue line represents the H2O snow surface. — astro-ph.EP
Rotational H2O spectra as observed with JWST/MIRI provide a good probe of the temperature and column density structure of the inner disk. H2O emission can also be influenced by dynamical processes, such as dust grains drifting inwards and their icy mantles sublimating once they cross the snowlines, thus enriching the inner regions in H2O vapor.
Recent work has found that this process may leave an imprint in the H2O spectrum in the form of excess flux in the cold H2O lines. In this work, we aim to test the accuracy of several common retrieval techniques on full 2D thermochemical disk models.
Moreover, we investigate the cold H2O emission that has been proposed as a signature of drift, to gain further insights into the underlying radial and vertical distribution of H2O. We present two sets of Dust And LInes (DALI) thermochemical models and run several retrieval techniques to investigate how the retrieved temperature and column density compare to our models.
Single-temperature slab retrievals mainly trace the warm (∼500 K) H2O reservoir, whereas a three-component fit is able to better trace the full temperature gradient in the IR emitting region. Retrieved temperatures tend to underestimate the true temperature of the emitting layer due to non-LTE effects. The retrieved column density traces close to the mid-IR dust τ=1 surface.
We find that the strength of the cold H2O emission is directly linked to the H2O abundance above the snow surface at large radii (>1 au). This implies that sources with excess cold H2O flux likely have a high H2O abundance in this region (≳10−5), higher than predicted by the chemical network. This discrepancy is most likely caused by the absence of dust transport processes in our models, further strengthening the theory that this emission may be a signature of radial drift and vertical mixing.
Marissa Vlasblom, Milou Temmink, Andrew D. Sellek, Ewine F. van Dishoeck
Comments: 19 pages, 20 figures, accepted for publication in Astronomy & Astrophysics
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2509.06494 [astro-ph.EP] (or arXiv:2509.06494v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2509.06494
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Submission history
From: Marissa Vlasblom
[v1] Mon, 8 Sep 2025 09:54:27 UTC (892 KB)
https://arxiv.org/abs/2509.06494
Astrobiology,
