Probing the kinematics and chemistry of the hot core Mon R 2 IRS 3 using ALMA observations

Abstract

We present high angular resolution 1.1mm continuum and spectroscopic ALMA observations of the well-known massive proto-cluster Mon R 2 IRS 3.The continuum image at 1.1mm shows two components, IRS 3 A and IRS 3 B, that are separated by $\sim$0.65$"$. We estimate that IRS 3 A is responsible of $\sim$80 % of the continuum flux, being the most massive component. We explore the chemistry of IRS 3 A based on the spectroscopic observations. In particular, we have detected intense lines of S-bearing species such as SO, SO${}_2$, H${}_2$CS and OCS, and of the Complex Organic Molecules (COMs) methyl formate (CH${}_3$OCHO) and dimethyl ether (CH${}_3$OCH${}_3$). The integrated intensity maps of most species show a compact clump centered on IRS 3 A, except the emission of the COMs that is more intense towards the near-IR nebula located to the south of IRS 3 A, and HC${}_3$N whose emission peak is located $\sim$0.5$"$ NE from IRS 3 A. The kinematical study suggests that the molecular emission is mainly coming from a rotating ring and/or an unresolved disk. Additional components are traced by the ro-vibrational HCN ${\nu }_2$=1 3$\to$2 line which is probing the inner disk/jet region, and the weak lines of CH${}_3$OCHO, more likely arising from the walls of the cavity excavated by the molecular outflow. Based on SO${}_2$ we derive a gas kinetic temperature of T${}_k$$\sim$ 170 K towards the IRS 3 A. The most abundant S-bearing species is SO${}_2$ with an abundance of $\sim$ 1.3$\times$10${}^{-7}$, and $\chi$(SO/SO${}_2$) $\sim$ 0.29. Assuming the solar abundance, SO${}_2$ accounts for $\sim$1 % of the sulphur budget.

12 pages, 8 figures, accepted for publication in MNRAS

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