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First Cospatial Mapping of H2O, CO2 and CO Ices Across a Molecular Cloud with JWST NIRCam WFSS

Zak, Smith

Publisher
Zenodo
DOI
10.5281/zenodo.17108869
Repository
zenodo.org
Language
en

Abstract

In the coldest regions of molecular clouds, carbon and oxygen are incorporated into icy dust grains. Ices play an essential role in star and planet formation where they set the initial chemical composition for future protoplanetary disks and chemical complexity. Despite this, ice's sequential formation is poorly constrained. Infrared spectroscopy probes ice chemistry, but previous telescopes observed insufficient sightlines to map a single cloud. JWST NIRCam Wide-Field Slitless Spectroscopy (WFSS) provides an excellent opportunity to do this. I present the first cospatial <1000AU-scale maps of H2O, CO2 and CO ice over the central region of the Chamaeleon I molecular cloud, using 44 sightlines along with the novel data reduction pipeline written to make WFSS a viable observing option. These observations show that ice species correlations, at densities ten times larger than previous work, suggest additional CO2 ice formation in CO ice for the densest sightlines. This large statistical sampling within a single cloud represents a step-change in constraining ice chemistry, eliminating averaging over clouds with different intrinsic chemical environments. This dataset adds a wealth of chemically-consistent observational constraints that can now be applied to pre-stellar phase astrochemical models. Mapping opens the door to probing gas-grain exchanges, snowlines, chemical evolution in the densest regions, and drawing conclusions on the impact of ice chemistry on wider astrophysics.

Full text

Cospatial Ice Mapping of H2O with CO2and CO Across a Molecular Cloud with JWST/NIRCam WFSS Dr. Zak Luka Smith Nature Astron. (Accepted and hopefully out in the coming days!) Z. L. Smith, H. J. Dickinson, H. J. Fraser, M. K. McClure, J. A. Noble, A. C. A. Boogert and the IceAge ERS team Tuesday, September 2, 2025 ESO: Towards New Frontiers – Garching, DE Conference Open Question: How much of molecular content in pre-stellar + protostellar systems is reprocessed or maintained in subsequent stages? Tuesday, September 2, 2025 ESO: Towards New Frontiers – Garching, DE 1 Studying Interstellar Ices at t=0 Tuesday, September 2, 2025 Image credit K. Peek Image credit: Boogert et al. 2015 Density dominated “Radiation” dominated ESO: Towards New Frontiers – Garching, DE 2 H2O-rich CO-rich CH3OH Phase Distillation Segregation Energetic Phase Tuesday, September 2, 2025 ESO: Towards New Frontiers – Garching, DE 3 •H2O, CO2 and CO make up >90% of ice material in early stages •CO2 formation in either H2Oor COrich ices •Basis from which COMs are formed •Variations relative to each other affect future possible chemistry Studying Interstellar Ices at t=0 H2O-rich CO-rich CH3OH phase Ice Mapping Technique Tuesday, September 2, 2025 NIRCam Spectral Range ESO: Towards New Frontiers – Garching, DE 4 McClure et al. 2023 (Figure 1) Pre-JWST Mapping •100s of sources with individual ice detections across multiple SF stages •If you want t=0 ices, must measure background stars in clouds •But only 23 BG stars have all H2O, CO2 and CO ices measured •Maximum 5 sources per cloud •Larger samples in the same molecular cloud are needed Tuesday, September 2, 2025 ESO: Towards New Frontiers – Garching, DE 5 Noble et al. (2017) Pontoppidan et al. (2004) Tuesday, September 2, 2025 Class 0 Class I BG Stars Chameleon I Cloud Image Credit: NASA/ESA/ F. Sun/Z. Smith/IceAge Team ESO: Towards New Frontiers – Garching, DE 6 Chameleon I Cloud Tuesday, September 2, 2025 Class 0 Class I BG Stars Image Credit: NASA/ESA/ F. Sun/Z. Smith/IceAge Team ESO: Towards New Frontiers – Garching, DE 7 Tuesday, September 2, 2025 ESO: Towards New Frontiers – Garching, DE 8 CO Ice Map Tuesday, September 2, 2025 ESO: Towards New Frontiers – Garching, DE 15 Correlation Plots Tuesday, September 2, 2025 ESO: Towards New Frontiers – Garching, DE 16 H2OCO2CO Correlation Plots Tuesday, September 2, 2025 ESO: Towards New Frontiers – Garching, DE 17 Non-linearities at high column densities! H2OCO2CO (44 sources) (23 sources) Relative Ice Ratios Tuesday, September 2, 2025 ESO: Towards New Frontiers – Garching, DE 18 Relative Ice Ratios Tuesday, September 2, 2025 ESO: Towards New Frontiers – Garching, DE 19 (44 sources) (23 sources) Overall higher percentages Relative Ice Ratios Tuesday, September 2, 2025 ESO: Towards New Frontiers – Garching, DE 20 (44 sources) (23 sources) Overall higher percentages Increased CO2 production in CO-rich ice Relative Total Ice Ratios Tuesday, September 2, 2025 ESO: Towards New Frontiers – Garching, DE 21 High total ice column Low total ice column Cha I Relative Total Ice Ratios Tuesday, September 2, 2025 ESO: Towards New Frontiers – Garching, DE 22 High total ice column Low total ice column Cha I Relative Total Ice Ratios Tuesday, September 2, 2025 ESO: Towards New Frontiers – Garching, DE 23 High total ice column Low total ice column Cha I ? ? ? Relative Total Ice Ratios Tuesday, September 2, 2025 ESO: Towards New Frontiers – Garching, DE 24 High total ice column Low total ice column Cha I Lower density regions of Cha I? NIRCam - Smith et al. 2025 (accepted) NIRSpec - McClure et al. 2023 (Smith Co-author) Tuesday, September 2, 2025 Species Column Density (N) NIR38: NIRCam WFSS ( ×1018 ) NIR38: NIRSpec FS (×1018) N(H2O) 7. 80 7.75 7.85 6.88 3.70 12.5 N(CO2)1.33 1.30 1.36 1.38 0.77 1.97 N(CO) 2.83 2.75 2.91 2.96 1.86 4.66 Our values compared with McClure 2023 ESO: Towards New Frontiers – Garching, DE 31 NIRCam Dispersion Tuesday, September 2, 2025 A 2.4μm 5μm F322W2 F444W 3.95μm F322W2 C B F322W2 R F444W R A B F444W C A B A B ESO: Towards New Frontiers – Garching, DE 32 Spectral Confusion Issue Tuesday, September 2, 2025 Module A Grism R Module A Grism C N N ESO: Towards New Frontiers – Garching, DE 33 How did we observe Cha I with JWST? L + M Band Filters 2 Dispersion Directions 2 visits 3 dithers 4 sub-pixel dithers 192 Dispersed Images Up to 96 images per source per filter Tuesday, September 2, 2025 ESO: Towards New Frontiers – Garching, DE 34 How did we observe Cha I with JWST? F322W2 filter (2.4-4μm) F444W filter (3.95-5μm) Tuesday, September 2, 2025 ESO: Towards New Frontiers – Garching, DE 35 Dangling OH Credit: Noble et al. 2024 Tuesday, September 2, 2025 ESO: Towards New Frontiers – Garching, DE 36 Scattering Effects in Clouds now! Credit: Dartois et al. 2024 Tuesday, September 2, 2025 ESO: Towards New Frontiers – Garching, DE 37 ED model fitting 2024 Tuesday, September 2, 2025 ESO: Towards New Frontiers – Garching, DE 38