JOYS+: Link Between Ice And Gas Of Complex Organic Molecules. Comparing JWST and ALMA Data of Two Low-mass Protostars
A rich inventory of complex organic molecules (COMs) has been observed in high abundances in the gas phase toward Class 0 protostars. These molecules are suggested to be formed in ices and sublimate in the warm inner envelope close to the protostar.
However, only the most abundant COM, methanol (CH3OH), has been firmly detected in ices before the era of James Webb Space Telescope (JWST). Now it is possible to detect the interstellar ices of other COMs and constrain their ice column densities quantitatively.
We aim to determine the column densities of several oxygen-bearing COMs (O-COMs) in both gas and ice for two low-mass protostellar sources, NGC 1333 IRAS 2A and B1-c, as case studies in our JWST Observations of Young protoStars (JOYS+) program.
Schematic of chemical evolution on dust grains in protostellar stages, modified from Fig. 1.4 of van ’t Hoff (2019) and Fig. 14 of Herbst & van Dishoeck (2009). Ice layers are dominated by different species (e.g., H2O, CO, and COMs) that are denoted in different colors. The typical temperature and density in different evolutionary stages are labeled on arrows in the bottom. The small red box indicates the hot core region where the temperature is high enough (>100 K) to sublimate most of the volatile materials and therefore the gas-phase molecules can be traced by radio telescopes at (sub-)millimeter wavelengths. The big blue box indicates that infrared telescopes such as JWST are tracing everything along the line of sight, including ice in the vast envelope and gas in the hot core. — astro-ph.SR
By comparing the column density ratios w.r.t. CH3OH between both phases measured in the same sources, we can probe into the evolution of COMs from ice to gas in the early stages of star formation. We are able to fit the fingerprints range of COM ices between 6.8 and 8.8 um in the JWST/MIRI-MRS spectra of B1-c using similar components as recently used for IRAS 2A.
We claim detection of CH4, OCN-, HCOO-, HCOOH, CH3CHO, C22H5OH, CH3OCH3, CH3OCHO, and CH3COCH3 in B1-c, and upper limits are estimated for SO2, CH3COOH, and CH3CN. The comparison of O-COM ratios w.r.t CH3OH between ice and gas shows two different cases.
1) the column density ratios of CH3OCHO and CH3OCH3 match well between the two phases, which may be attributed to a direct inheritance from ice to gas or strong chemical links with CH3OH.
2) the ice ratios of CH3CHO and C2H5OH w.r.t. CH3OH are higher than the gas ratios by 1-2 orders of magnitudes.
This difference can be explained by the gas-phase reprocessing following sublimation, or different spatial distributions of COMs in the envelope.
Y. Chen, W. R. M. Rocha, E. F. van Dishoeck, M. L. van Gelder, P. Nazari, K. Slavicinska, L. Francis, B. Tabone, M. E. Ressler, P. D. Klaassen, H. Beuther, A. C. A. Boogert, C. Gieser, P. J. Kavanagh, G. Perotti, V. J. M. Le Gouellec, L. Majumdar, M. Güdel, Th. Henning
Comments: 42 pages (22 main text, 20 appendix); 27 figures (12 in main text, 15 in appendix); 5 tables (2 in main text, 3 in appendix) Accepted for publication in A&A
Subjects: Astrophysics of Galaxies (astro-ph.GA); Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:2407.20066 [astro-ph.GA] (or arXiv:2407.20066v1 [astro-ph.GA] for this version)
Submission history
From: Yuan Chen
[v1] Mon, 29 Jul 2024 14:53:40 UTC (25,967 KB)
https://arxiv.org/abs/2407.20066
Astrobiology,
