Arp 220: New Observational Insights into the Structure and Kinematics of the Nuclear Molecular Disks and Surrounding Gas

TL;DR

This study uses ALMA observations to analyze the molecular gas structure and kinematics in Arp 220's nuclei, revealing tidal features, outflows, and complex gas dynamics through detailed modeling.

Contribution

It provides new high-resolution observational data and non-LTE radiative transfer models to understand the gas dynamics and physical conditions in Arp 220's nuclear regions.

Findings

Detection of m=2 tidal features indicating gas inflow.

Identification of outflows in both nuclei.

Western nucleus is optically thick even in less abundant molecules.

Abstract

ALMA cycle 3 observations of $^{12}$CO $ J = 3\rightarrow2$, $^{13}$CO $J = 4\rightarrow 3$, SiO J = $8 \rightarrow 7$, and HCN J = $ 5 \rightarrow 4$ are presented. Significant extended emission is detected in $^{12}$CO J $ = 3\rightarrow2$ with a morphology that is indicative of m = 2 tidal features, suggesting gas inflow. In addition, outflow for both nuclei are found in the $^{12}$CO J $ = 3\rightarrow2$. Significant SiO absorption is detected in the western nucleus. HCN that is morphologically distinct from CO is detected in both nuclei. These observations are compared to non-LTE radiative transfer models created using the Line Modeling Engine (LIME) for simple gas dynamics to gain insight into how physical parameters, such as rotational velocity, turbulent velocity, gas temperature, dust temperature, and gas mass can reproduce the observed kinematic and spatial features. The eastern nucleus is found to be best modeled with an inclusion of a temperature asymmetry from one side of the disk to the other. It is also found that the western nucleus is optically thick even in the less abundant species of $^{13}$CO, absorbing significant amounts of continuum radiation.