2021MNRAS.507.1886F

We present high angular resolution 1.1 mm continuum and spectroscopic Atacama Large Millimeter/submillimeter Array observations of the well-known massive protocluster Mon R2 IRS 3. The continuum image at 1.1 mm shows two components, IRS 3 A and IRS 3 B, that are separated by ∼0.65 arcsec. We estimate that IRS 3 A is responsible of ∼80 per cent of the continuum flux, being the most massive component. We explore the chemistry of IRS 3 A based on the spectroscopic observations. In particular, we have detected intense lines of S-bearing species such as SO, SO₂, H₂CS, and OCS, and of the complex organic molecules (COMs) methyl formate (CH₃OCHO) and dimethyl ether (CH₃OCH₃). The integrated intensity maps of most species show a compact clump centred on IRS 3 A, except the emission of the COMs that is more intense towards the near-IR nebula located to the south of IRS 3 A, and HC₃N whose emission peak is located ∼0.5 arcsec NE from IRS 3 A. The kinematical study suggests that the molecular emission is mainly coming from a rotating ring and/or an unresolved disc. Additional components are traced by the ro-vibrational HCN ν₂ = 1 3-2 line which is probing the inner disc/jet region, and the weak lines of CH₃OCHO, more likely arising from the walls of the cavity excavated by the molecular outflow. Based on SO₂ we derive a gas kinetic temperature of T_k∼170 K towards the IRS 3 A. The most abundant S-bearing species is SO₂ with an abundance of ∼ 1.3 x 10^–7, and χ(SO/SO₂) ∼ 0.29. Assuming the solar abundance, SO₂ accounts for ∼1 per cent of the sulphur budget.