Probing the kinematics and chemistry of the hot core Mon R2 IRS 3 using ALMA observations

Abstract

ABSTRACT 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$_k\, \sim$ 170 K towards the IRS 3 A. The most abundant S-bearing species is SO2 with an abundance of ∼ 1.3 × 10−7, and χ(SO/SO2) ∼ 0.29. Assuming the solar abundance, SO2 accounts for ∼1 per cent of the sulphur budget.