First Detection Of Ices In Intermediate-mass Young Stellar Objects Beyond The Milky Way

Using NIRSpec on JWST, we studied a sample of 15 intermediate-mass (1.8-4.1 M_sun) young stellar objects (YSOs) previously identified with MIRI photometry in the low-metallicity NGC 346 star-forming cluster in the Small Magellanic Cloud (SMC).

All objects, observed in the 1.7-5.3 micron range, show strong hydrogen recombination lines in the Paschen, Brackett, Pfund, and Humphreys series, confirming their very young ages. The spectra of 11 YSOs show prominent absorption bands from the three most important ice species (H₂O, CO₂, CO), marking the first detection of these ices in intermediate-mass YSOs beyond our Galaxy. In three YSOs, water ice appears to be in crystalline form.

In some objects, we also detect ¹³CO₂ and OCS ices — never before observed beyond the Milky Way (MW) — and methanol ice in at least one star. We compared the column densities of H₂O, CO₂, and CO ices with those measured in more and less massive protostars in the MW and Large Magellanic Cloud, finding that in NGC 346 ice column densities reach values nearly an order of magnitude lower than in more massive objects (~1×10^{17} cm-2 for water and ~1×10^{16} cm-2 for CO₂ and CO).

However, the relative proportions of the ice species abundances do not differ from those in massive MW YSOs. This suggests that metallicity may not significantly affect ice chemistry in protoplanetary discs and that, shielded by the protostellar envelope or deep in the midplane, circumstellar material is likely impervious to the radiation environment.

Guido De Marchi, Nolan Habel, Margaret Meixner, Katia Biazzo, Giovanna Giardino, Elena Sabbi, Ciaran Rogers, Jeroen Jaspers, Massimo Robberto, Peter Zeidler, Olivia C. Jones, Katja Fahrion, Alec S. Hirschauer, Charles D. Keyes, David R. Soderblom, Laura Lenkic, Omnarayani Nayak, Bernhard Brandl

Comments: 18 pages, 5 figures, accepted for publication in The Astrophysical Journal
Subjects: Astrophysics of Galaxies (astro-ph.GA); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:2509.13315 [astro-ph.GA] (or arXiv:2509.13315v1 [astro-ph.GA] for this version)
https://doi.org/10.48550/arXiv.2509.13315
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Submission history
From: Guido De Marchi
[v1] Tue, 16 Sep 2025 17:59:03 UTC (1,690 KB)
https://arxiv.org/abs/2509.13315

Astrochemistry, Astrobiology,