Three Dimensional Line Transfer Study of Energy Sources in Compact Molecular Gas in Active Galaxies -- AGN/Starburst Connection --

TL;DR

This study uses advanced 3D non-LTE line transfer simulations to analyze molecular line ratios in active galaxies, revealing conditions for distinguishing energy sources like AGN and starburst activity.

Contribution

First realistic 3D simulations demonstrating the impact of clumpiness on molecular line ratios, aiding interpretation of galaxy energy sources.

Findings

Identified conditions for HCN/HCO+ ratio dichotomy.

Showed importance of molecular gas clumpiness on line intensity ratios.

Established the potential of line transfer simulations for extragalactic ISM studies.

Abstract

Recent observations suggest molecular line ratios in millimeter and submillimeter bands may be a good tool to reveal the long-standing question on the origin of energy sources in obscured active galaxies -- AGN and/or starburst. Observations of actual molecular medium show in general inhomogeneous structures as well as high-resolution hydrodynamic simulations do. In order for precise interpretation of emergent line emission from the inhomogeneous molecular gas to probe the dominant energy source of active galaxies, we study characteristic features of emergent intensities via three-dimensional non-LTE (non-local thermodynamic equilibrium) line transfer simulations. Our results succeeded in making clear 1) the necessary conditions for HCN/HCO$^{+}$-dichotomy, and 2) importance of clumpiness on intensity ratio and its interpretation. These results are obtained for the first time by our realistic three-dimensional simulations, and line transfer simulations will be a powerful tool to comprehensive studies of extragalactic interstellar medium (ISM) in forthcoming ALMA (Atacama Large Millimeter/submillimeter Array) era.