ATOMS: ALMA three-millimeter observations of massive star-forming regions – XIX. The origin of SiO emission

Abstract

ABSTRACT The production of silicon monoxide (SiO) can be considered as a fingerprint of shock interaction. In this work, we use high-sensitivity observations of the SiO (2–1) and H$^{13}$CO$^{+}$ (1–0) emission to investigate the broad and narrow SiO emission towards 146 massive star-forming regions in the ATOMS (ALMA Three-millimeter Observations of Massive Star-forming regions) survey. We detected SiO emission in 136 regions and distinguished broad and narrow components across the extension of 118 sources (including 58 UC H ii regions) with an average angular resolution of 2.5 arcsec. The derived SiO luminosity ($L_{\rm SiO}$) across the whole sample shows that the majority of $L_{\rm SiO}$ (above 66 per cent) can be attributed to broad SiO, indicating its association with strong outflows. The comparison of the ALMA SiO images with the filamentary skeletons identified from H$^{13}$CO$^{+}$ and in the infrared data (at 4.5, 8, and 24 μm), further confirms that most SiO emission originates from outflows. However, note that for nine sources in our sample, the observed SiO emission may be generated by expanding UC H ii regions. There is a moderate positive correlation between the bolometric luminosity ($L_{\rm bol}$) and $L_{\rm SiO}$ for both components (narrow and broad). The UC H ii sources show a weaker positive correlation between $L_{\rm bol}$ and $L_{\rm SiO}$ and higher $L_{\rm SiO}$ compared to the sources without UC H ii regions. These results imply that the SiO emission from UC H ii sources might be affected by UV-photochemistry induced by UC H ii regions.