ALMA Observations of the Massive Molecular Outflow G331.512-0.103. II. Physical Properties, Kinematics, and Geometry Modeling

Abstract

We present observations and analysis of the massive molecular outflow G331.512-0.103, obtained with ALMA band 7, continuing the work from Merello et al. (2013). Several lines were identified in the observed bandwidth, consisting of two groups: lines with narrow profiles, tracing the emission from the core ambient medium; and lines with broad velocity wings, tracing the outflow and shocked gas emission. The physical and chemical conditions, such as density, temperature, and fractional abundances are calculated. The ambient medium, or core, has a mean density of $\\sim 5\\times 10^6$ cm$^{-3}$ and a temperature of $\\sim 70$ K. The SiO and SO$_2$ emission trace the very dense and hot part of the shocked outflow, with values of $n_{\\rm H_2}\\sim10^9$ cm$^{-3}$ and $T \\sim 160-200$ K. The interpretation of the molecular emission suggests an expanding cavity geometry powered by stellar winds from a new-born UCHII region, alongside a massive and high-velocity molecular outflow. This scenario, along with the estimated physical conditions, is modeled using the 3D geometry radiative transfer code MOLLIE for the SiO(J$=8-7$) molecular line. The main features of the outflow and the expanding shell are reproduced by the model.