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PreprintCC BY 4.0arXiv

H2O emission as tracer of pebble drift: insights from coupling transport and thermochemical models

  • Marissa Vlasblom
  • Andrew D. Sellek
  • Ewine F. van Dishoeck
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Abstract

(Abridged) The composition of the inner regions of protoplanetary disks is known to change with time due to the delivery of icy grains. Cold H2O emission seen with JWST-MIRI is often hypothesized to be a tracer of this pebble drift. However, it is unclear to what extent processes such as photodissociation or the co-delivery of dust may impede such detections. We aim to obtain an improved, 2D view of transport in disks, to better understand how these processes can be traced by H2O emission as seen with JWST-MIRI. We combine the 1D transport code DiscEvolution with the 2D thermochemical code DALI to create several grids of models in which the gas-phase abundances, dust properties, or both are varied according to the transport model. We consider scenarios with and without a traffic jam inside the H2O snowline. The transport of both gas and dust leads to significant temperature changes within the disk, which strongly influence line fluxes and ratios. When a traffic jam is present, the delivery of H2O can proceed unnoticed due to the co-delivery of dust. In addition, the relative strength of cold H2O lines is not found to be sensitive to this delivery of gas-phase H2O. Instead, the cold H2O lines can be greatly enhanced by the delivery of only dust to the inner disk when a traffic jam is present, and one can create a spectrum with strong cold H2O emission solely through the delivery of dust rather than H2O. Recent work has used the 1500/6000 K H2O line ratio as a proxy to determine the pebble mass flux crossing the H2O snowline, but we find that this line ratio is rather sensitive to the temperature and dust distribution of the disk, and is often influenced not only by the cold H2O mass, but also by the hot H2O mass. This introduces complexities and trends as a function of time that do not match the true evolution of the pebble flux.

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Cite

BibTeXRIS
BibTeX
@misc{vlasblom2026emission,
  title = {{H$_2$O emission as tracer of pebble drift: insights from coupling transport and thermochemical models}},
  author = {Marissa Vlasblom and Andrew D. Sellek and Ewine F. van Dishoeck},
  howpublished = {arXiv},
  year = {2026},
  month = sep,
  doi = {10.48550/arxiv.2609.16808},
  eprint = {2609.16808},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2609.16808},
  note = {CC BY 4.0},
}
RIS
TY  - UNPB
TI  - H_2O emission as tracer of pebble drift: insights from coupling transport and thermochemical models
AU  - Marissa Vlasblom
AU  - Andrew D. Sellek
AU  - Ewine F. van Dishoeck
PY  - 2026
DA  - 2026/09/15
PB  - arXiv
DO  - 10.48550/arxiv.2609.16808
UR  - https://arxiv.org/abs/2609.16808
AB  - (Abridged) The composition of the inner regions of protoplanetary disks is known to change with time due to the delivery of icy grains. Cold H_2O emission seen with JWST-MIRI is often hypothesized to be a tracer of this pebble drift. However, it is unclear to what extent processes such as photodissociation or the co-delivery of dust may impede such detections. We aim to obtain an improved, 2D view of transport in disks, to better understand how these processes can be traced by H_2O emission as seen with JWST-MIRI. We combine the 1D transport code DiscEvolution with the 2D thermochemical code DALI to create several grids of models in which the gas-phase abundances, dust properties, or both are varied according to the transport model. We consider scenarios with and without a traffic jam inside the H_2O snowline. The transport of both gas and dust leads to significant temperature changes within the disk, which strongly influence line fluxes and ratios. When a traffic jam is present, the delivery of H_2O can proceed unnoticed due to the co-delivery of dust. In addition, the relative strength of cold H_2O lines is not found to be sensitive to this delivery of gas-phase H_2O. Instead, the cold H_2O lines can be greatly enhanced by the delivery of only dust to the inner disk when a traffic jam is present, and one can create a spectrum with strong cold H_2O emission solely through the delivery of dust rather than H_2O. Recent work has used the 1500/6000 K H_2O line ratio as a proxy to determine the pebble mass flux crossing the H_2O snowline, but we find that this line ratio is rather sensitive to the temperature and dust distribution of the disk, and is often influenced not only by the cold H_2O mass, but also by the hot H_2O mass. This introduces complexities and trends as a function of time that do not match the true evolution of the pebble flux.
ER  -