A Mid-infrared Spectroscopic Study of Young Stellar Objects in the SMC Region NGC 346: JWST Detects Dust, Accretion, Ices, and Outflows

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Abstract
We present mid-infrared spectroscopic observations of intermediate-to-high-mass young stellar objects (YSOs) in the low-metallicity star-forming region NGC 346 located within the Small Magellanic Cloud (SMC). We conduct these integral field unit observations with the Medium Resolution Spectroscopy mode of the Mid-Infrared Instrument on board JWST. The brightest and most active star-forming region in the SMC, NGC 346, has a metallicity of ∼1/5 Z ⊙ , analogous to the era when star formation in the early Universe ( z ≃ 2) peaked. We discuss the emission and absorption features present in the spectral energy distributions (SEDs) of five YSOs with coverage from 4.9 to 27.9 μ m and three other sources with partial spectral coverage. Via SED model fitting, we estimate their parameters, finding masses ranging from 2.9 to 18.0 M ⊙ . These targets show dusty silicates, polycyclic aromatic hydrocarbons, and ices of CO 2 , CO, H 2 O, and CH 3 OH in their protostellar envelopes. We measure emission from H 2 and atomic fine-structure lines, suggesting the presence of protostellar jets and outflows. We detect H i lines, indicating ongoing accretion, and estimate accretion rates for each source that range from 2.50 × 10 −6 to 2.23 × 10 −4 M ⊙ yr −1 , based on the H i (7–6) line emission. We present evidence for a ∼30,000 au protostellar jet traced by fine-structure, H i , and H 2 emission about YSO Y535—the first mid-infrared detection of a resolved protostellar outflow in the SMC and the most distant yet detected by JWST.
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  • NASA ∣ Jet Propulsion Laboratory (JPL Task Plan No. 71-209636)

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