Thermal Balance in Dense Molecular Clouds: Radiative Cooling Rates and Emission-Line Luminosities

Abstract

We consider the radiative cooling of fully shielded molecular astrophysical gas over a wide range of temperatures (10K ≤ T ≤ 2500K) and H<SUB>2</SUB> densities (l0<SUP>3</SUP> cm<SUP>-3</SUP> ≤ n(H<SUB>2</SUB>) ≤ 10<SUP>10</SUP> cm<SUP>-3</SUP>). Our model for the radiative cooling of molecular gas includes a detailed treatment of the interstellar chemistry that determines the abundances of important coolant molecules, and a detailed treatment of the excitation of the species H<SUB>2</SUB>, CO, H<SUB>2</SUB>O, HC1, O<SUB>2</SUB>, C, O, and their isotopic variants where important. We present results for the total radiative cooling rate and for the cooling rate due to individual coolant species, as a function of the gas temperature, density, and optical depth. We have also computed the individual millimeter, submillimeter, and far-infrared line strengths that contribute to the total radiative cooling rate, and we have obtained example spectra for the submillimeter emission expected from molecular cloud cores. Many of the important cooling lines will be detectable using the Infrared Space Observatory and the Submillimeter Wave Astronomy Satellite.