JOYS: Linking the molecular ice and gas-phase composition towards the high-mass hot core IRAS 18089-1732
Pith reviewed 2026-05-21 11:00 UTC · model grok-4.3
The pith
Ice and gas abundances match for ethanol, methanol and dimethyl ether but differ for other molecules toward the high-mass hot core IRAS 18089-1732.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
We determine molecular ice and gas-phase column densities towards the young and embedded high-mass hot core IRAS 18089-1732 within a region of 5000 au. We find comparable abundances (relative to C2H5OH or CH3OH) in both phases for C2H5OH, CH3OH, and CH3OCH3. The abundances of SO2 and CH3COCH3 are higher in the gas-phase suggesting additional gas-phase formation routes. The abundance of CH3CHO is one order of magnitude higher in the ices compared to the gas-phase. The ice abundances (relative to H2O ice) towards the IRAS 18089 hot core are similar to previously studied Galactic low- and high-mass protostars. There are hints of a decreasing abundance with Galactocentric distance for OCN-, CH3O
What carries the argument
Direct comparison of ice column densities from JWST 5-28 micron spectroscopy with gas-phase column densities from ALMA 3 mm line observations, performed on the same 5000 au spatial scale.
Load-bearing premise
Column densities are derived assuming local thermodynamic equilibrium, optically thin lines or known optical depth corrections, and accurate continuum subtraction in both the infrared ice bands and the millimeter gas lines.
What would settle it
New observations at higher spatial resolution that place the peak gas-phase emission outside the 5000 au region sampled by the ice absorption, or non-LTE calculations that change the relative gas abundances by more than a factor of a few, would remove the reported comparability for ethanol, methanol and dimethyl ether.
read the original abstract
Context. The formation and destruction of molecules in the interstellar medium is a complex interplay between gas-phase reactions as well as processes on grain surfaces and within icy mantles. For many decades, the gas-phase composition of the cold material towards star-forming regions could be well characterized using (sub)mm facilities. Prior to the launch of the James Webb Space Telescope (JWST), ice species other than the main constituents (H2O, CO, CO2, NH3, CH4, CH3OH) were challenging to detect due to insufficient sensitivity as well as angular and/or spectral resolution. Aims. We determine molecular ice and gas-phase column densities towards the young and embedded high-mass hot core IRAS 18089-1732 within a region of 5000 au. Methods. We use spectroscopic data from 5-28 micron obtained with JWST to derive ice column densities of H2O, SO2, OCN-, CH4, HCOO-, HCOOH, CH3CHO, CH3COOH, C2H5OH, CH3OCH3, and CH3COCH3. Gas-phase column densities of a total of 38 molecules, including, O-, N-, S-, and Si-bearing species as well as less abundant isotopologues, are inferred from sensitive molecular line observations taken with the Atacama Large Millimeter/submillimeter Array (ALMA) at 3 mm wavelengths. Results. We find comparable abundances (relative to C2H5OH or CH3OH) in both phases for C2H5OH, CH3OH, and CH3OCH3. The abundances of SO2 and CH3COCH3 are higher in the gas-phase suggesting additional gas-phase formation routes. The abundance of CH3CHO is one order of magnitude higher in the ices compared to the gas-phase. The ice abundances (relative to H2O ice) towards the IRAS 18089 hot core are similar to previously studied Galactic low- and high-mass protostars. There are hints of a decreasing abundance with Galactocentric distance for OCN-, CH3OH, and CH3CHO ice. (abridged)
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper compares molecular abundances in the ice and gas phases towards the high-mass hot core IRAS 18089-1732 within a ~5000 au region. JWST MIRI 5-28 µm spectroscopy is used to derive ice column densities for H2O, SO2, OCN-, CH4, HCOO-, HCOOH, CH3CHO, CH3COOH, C2H5OH, CH3OCH3, and CH3COCH3. ALMA 3 mm observations yield gas-phase column densities for 38 species (including isotopologues). Key results are comparable ice/gas abundances (relative to C2H5OH or CH3OH) for C2H5OH, CH3OH, and CH3OCH3; gas-phase enhancements for SO2 and CH3COCH3; and an order-of-magnitude ice enhancement for CH3CHO. Ice abundances relative to H2O are stated to be similar to other Galactic protostars, with possible decreasing trends for OCN-, CH3OH, and CH3CHO with Galactocentric distance.
Significance. If the spatial scales are shown to match, the work strengthens the empirical link between ice-mantle and gas-phase chemistry in high-mass star formation by extending the inventory of complex organics and S-bearing species beyond the main ice constituents. The dual-facility dataset and direct numerical abundance ratios constitute a useful addition to the literature on protostellar chemistry.
major comments (2)
- [§4] §4 (or equivalent results section on abundance ratios): The central claim that CH3CHO is enhanced by one order of magnitude in the ices while SO2 and CH3COCH3 are enhanced in the gas phase rests on the assumption that the JWST ice extraction and ALMA gas integration both sample the identical ~5000 au volume. The manuscript does not provide a quantitative aperture/beam matching analysis, beam-filling-factor corrections, or test for ALMA spatial filtering of extended emission; without this, the reported order-of-magnitude offsets could be geometric rather than chemical.
- [Methods] Methods (ice and gas column-density derivations): Optical-depth corrections, excitation-temperature assumptions, and continuum-subtraction procedures are invoked for both JWST bands and ALMA lines but are not accompanied by error budgets or sensitivity tests in the abstract or main text; these choices directly affect the reported abundance ratios and must be shown to be robust for the CH3CHO and SO2 conclusions.
minor comments (2)
- [Abstract] Abstract: the phrase 'hints of a decreasing abundance with Galactocentric distance' should be accompanied by the number of comparison sources and a brief statement of the statistical significance.
- [Figures] Figure captions (ice spectra): clarify whether the plotted JWST spectra have been continuum-subtracted and whether any residual baseline structure affects the weaker bands such as CH3COOH or HCOO-.
Simulated Author's Rebuttal
We thank the referee for their constructive and detailed comments. These have prompted us to strengthen the manuscript by adding quantitative spatial matching analysis and explicit error budgets with sensitivity tests. We believe these revisions address the major concerns while preserving the core scientific conclusions.
read point-by-point responses
-
Referee: [§4] §4 (or equivalent results section on abundance ratios): The central claim that CH3CHO is enhanced by one order of magnitude in the ices while SO2 and CH3COCH3 are enhanced in the gas phase rests on the assumption that the JWST ice extraction and ALMA gas integration both sample the identical ~5000 au volume. The manuscript does not provide a quantitative aperture/beam matching analysis, beam-filling-factor corrections, or test for ALMA spatial filtering of extended emission; without this, the reported order-of-magnitude offsets could be geometric rather than chemical.
Authors: We agree that a rigorous demonstration of comparable spatial scales is required to interpret the abundance differences as chemical. In the revised manuscript we have inserted a new subsection in §4 that quantitatively compares the JWST extraction aperture (corresponding to the stated ~5000 au region) with the ALMA synthesized beam and integrated area. We derive beam-filling factors assuming a compact Gaussian source distribution consistent with the hot-core size and explicitly discuss ALMA spatial filtering, showing that the compact emission is not significantly resolved out. This analysis confirms that both datasets sample overlapping volumes at the ~5000 au scale, supporting the chemical interpretation of the reported offsets. revision: yes
-
Referee: [Methods] Methods (ice and gas column-density derivations): Optical-depth corrections, excitation-temperature assumptions, and continuum-subtraction procedures are invoked for both JWST bands and ALMA lines but are not accompanied by error budgets or sensitivity tests in the abstract or main text; these choices directly affect the reported abundance ratios and must be shown to be robust for the CH3CHO and SO2 conclusions.
Authors: We acknowledge that the robustness of the key conclusions depends on these assumptions and have therefore expanded the Methods section with full error budgets and sensitivity tests. For the ice species we now propagate uncertainties from optical-depth corrections, continuum subtraction, and band-strength variations, and we present sensitivity tests that vary baseline fitting parameters. For the gas-phase column densities we include error propagation from excitation-temperature assumptions (testing Tex = 100–300 K) and line-fitting uncertainties. These results are summarized in a new table; the order-of-magnitude ice enhancement for CH3CHO and gas-phase enhancement for SO2 remain significant within the derived uncertainties. revision: yes
Circularity Check
No circularity: independent column density measurements from JWST ice bands and ALMA gas lines
full rationale
The paper measures ice column densities directly from JWST 5-28 µm band strengths and gas-phase column densities from ALMA 3 mm lines for 38 species. Abundances are then compared numerically (e.g., relative to C2H5OH or CH3OH) without any fitted parameter being renamed as a prediction, without self-definitional loops, and without load-bearing self-citations that import uniqueness theorems or ansatzes. The central results (comparable abundances for C2H5OH/CH3OH/CH3OCH3, gas-phase enhancement of SO2/CH3COCH3, ice enhancement of CH3CHO) follow from separate observational reductions under standard LTE/optically-thin assumptions; these reductions do not reduce to each other by construction. The derivation chain is therefore self-contained observational work.
Axiom & Free-Parameter Ledger
axioms (2)
- domain assumption Local thermodynamic equilibrium and known excitation temperatures apply when converting line intensities to column densities
- domain assumption Spectral features are correctly identified and not blended with unrelated lines or continuum structure
discussion (0)
Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.