$K$-band integral field spectroscopy and optical spectroscopy of massive young stellar objects in the Small Magellanic Cloud

Abstract

We present $K$-band integral field spectroscopic observations towards 17 massive young stellar objects (YSOs) in the low metallicity Small Magellanic Cloud (SMC) and two YSO candidates in the compact H ii regions N81 and N88 A (also in the SMC). These sources, originally identified using $Spitzer$ photometry and/or spectroscopy, have been resolved into 29 $K$-band continuum sources. By comparing Br$\gamma$ emission luminosities with those presented for a Galactic sample of massive YSOs, we find tentative evidence for increased accretion rates in the SMC. Around half of our targets exhibit emission line (Br$\gamma$, He i and H${}_2$) morphologies which extend significantly beyond the continuum source and we have mapped both the emission morphologies and the radial velocity fields. This analysis also reveals evidence for the existence of ionized low density regions in the centre outflows from massive YSOs. Additionally we present an analysis of optical spectra towards a similar sample of massive YSOs in the SMC, revealing that the optical emission is photo-excited and originates near the outer edges of molecular clouds, and is therefore consistent with a high mean-free path of UV photons in the interstellar medium (ISM) of the SMC. Finally, we discuss the sample of YSOs in an evolutionary context incorporating the results of previous infrared and radio observations, as well as the near-infrared and optical observations presented in this work. Our spectroscopic analysis in both the $K$-band and the optical regimes, combined with previously obtained infrared and radio data, exposes differences between properties of massive YSOs in our own Galaxy and the SMC, including tracers of accretion, discs and YSO--ISM interactions.

42 pages, 22 figures, Accepted for publication in MNRAS 2016 September 16

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• The Detection of Hot Molecular Cores in the Small Magellanic Cloud
• CO(2-1) Survey at 9 parsec resolution in the SMC
• Massive young stellar objects in the Local Group irregular galaxy NGC6822 identified using machine learning
• A dearth of OH/IR stars in the Small Magellanic Cloud
• Herschel spectroscopy of Massive Young Stellar Objects in the Magellanic Clouds
• The First Detection of a Protostellar CO Outflow in the Small Magellanic Cloud with ALMA
• Resolved star formation in the metal poor star-forming region Magellanic Bridge C
• X3: a high-mass Young Stellar Object close to the supermassive black hole Sgr~A*
• Near-infrared spectroscopy of embedded protostars in the massive metal-poor star-forming region NGC 346
• Massive young stellar objects in the Local Group spiral galaxy M33 identified using machine learning
• Investigating the Impact of Metallicity on Star Formation in the Outer Galaxy. I. VLT/KMOS Survey of Young Stellar Objects in Canis Major
• ALMA 0.1 pc View of Molecular Clouds Associated with High-Mass Protostellar Systems in the Small Magellanic Cloud: Are Low-Metallicity Clouds Filamentary or Not?