Caltech/IPAC Lunch Seminar

NGC 346 is the brightest and most active star-forming region in the Small Magellanic Cloud (SMC). With a metallicity of ~1/5 Z solar, it is a local analog of galaxies that formed at cosmic noon, the era when star formation in the early Universe (Z = ~2) was at its peak, and metallicity was lower. Here we present mid-infrared spectroscopic observations of some of the most embedded intermediate-to-high-mass young stellar objects (YSOs) within this region. We conduct these integral field unit observations with the Medium Resolution Spectroscopy mode of the Mid-Infrared Instrument on board JWST. Narrow emission features are present in the spectral energy distributions (SEDs) of five YSOs with coverage from 4.9 to 27.9 microns and three other sources with partial spectral coverage; we discuss the line species detected and their origins within the forming protostars. Via SED model fitting, we estimate the physical parameters of these YSOs, finding masses ranging from 2.9 to 18.0 solar masses. These targets show dusty silicates, polycyclic aromatic hydrocarbons, and ices of CO2, CO, H2O, and CH3OH in their protostellar envelopes, but to a lesser extent than counterpart YSOs at higher-metallicity, indicating a lower overall dust and ice content. By comparing the relative strength of the PAH features, we see evidence of increased dust destruction at more evolved stages. We measure emission from H2 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. Finally, we present evidence for a ∼30,000 au protostellar jet traced by fine-structure, H I, and H2 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.