2023MNRAS.525.6146W

We present a study of the physical and chemical properties of the Extended Green Object (EGO) G19.01-0.03 using sub-arcsecond angular resolution Atacama Large Millimetre/submillimetre Array (ALMA) 1.05 mm and Karl G. Jansky Very Large Array (VLA) 1.21 cm data. G19.01-0.03 MM1, the millimetre source associated with the central massive young stellar object (MYSO), appeared isolated and potentially chemically young in previous Submillimetre Array observations. In our ∼0.4 arcsec-resolution ALMA data, MM1 has four low-mass millimetre companions within 0.12 pc, all lacking maser or outflow emission, indicating they may be pre-stellar cores. With a rich ALMA spectrum full of complex organic molecules, MM1 does not appear chemically young, but has molecular abundances typical of high-mass hot cores in the literature. At the 1.05 mm continuum peak of MM1, N(CH₃OH) = (2.22 ± 0.01) × 10¹⁸ cm^–2 and $T_{\mathrm{ex}} = 162.7\substack{+0.3 \\ -0.5}$ K based on pixel-by-pixel Bayesian analysis of LTE synthetic methanol spectra across MM1. Intriguingly, the peak CH₃OH T_ex = 165.5 ± 0.6 K is offset from MM1's millimetre continuum peak by 0.22 arcsec ∼ 880 au, and a region of elevated CH₃OH T_ex coincides with free-free VLA 5.01 cm continuum, adding to the tentative evidence for a possible unresolved high-mass binary in MM1. In our VLA 1.21 cm data, we report the first NH₃(3,3) maser detections towards G19.01-0.03, along with candidate 25 GHz CH₃OH 5(2, 3) - 5(1, 4) maser emission; both are spatially and kinematically coincident with 44 GHz Class I CH₃OH masers in the MM1 outflow. We also report the ALMA detection of candidate 278.3 GHz Class I CH₃OH maser emission towards this outflow, strengthening the connection of these three maser types to MYSO outflows.