A recent update of gas-phase chemical reactions and molecular lines in CLOUDY: its effects on millimeter and sub-millimeter molecular line predictions

TL;DR

This paper updates the spectral synthesis code CLOUDY with new gas-phase chemical reactions and molecular line data, enhancing its accuracy in modeling astrophysical environments for millimeter and sub-millimeter observations.

Contribution

The paper introduces 561 new reactions and updates existing molecular data in CLOUDY, enabling comprehensive predictions of molecular lines from nine molecules in various astrophysical settings.

Findings

Successfully modeled ArH$^+$ in Crab nebula globules.

Predicted detectable levels of HeH$^+$, OH$^+$, and CH$^+$ in Crab nebula.

Predictions closely match observed column densities in multiple environments.

Abstract

Here we present our current updates of the gas-phase chemical reaction rates and molecular lines in the spectral synthesis code CLOUDY, and its implications in spectroscopic modelling of various astrophysical environments. We include energy levels, radiative and collisional rates for HF, CF$^+$, HC$_3$N, ArH$^+$, HCl, HCN, CN, CH, and CH$_2$. Simultaneously, we expand our molecular network involving these molecules. For this purpose, we have added 561 new reactions and have updated the existing 165 molecular reaction rates involving these molecules. As a result, CLOUDY now predicts all the lines arising from these nine molecules. In addition, we also update H$_2$--H$_2$ collisional data up to rotational levels $J$=31 for $v$=0. We demonstrate spectroscopic simulations of these molecules for a few astrophysical environments. Our existing model for globules in the Crab nebula successfully predicts the observed column density of ArH$^+$. Our model predicts a detectable amount of HeH$^+$, OH$^+$, and CH$^+$ for the Crab nebula. We also model the ISM towards HD185418, W31C, NGC 253, and our predictions match with most of the observed column densities within the observed error bars. Very often molecular lines trace various physical conditions. Hence, this update will be very supportive for spectroscopic modelling of various astrophysical environments, particularly involving sub-millimeter and mid-infrared observations using ALMA and JWST, respectively.