H_2^{16}O and H_2^{18}O Maser Emission from Gas-Dust Clouds

TL;DR

This study uses numerical simulations to analyze collisional pumping of H_2^{16}O and H_2^{18}O masers in dense gas-dust clouds, exploring conditions for detecting H_2^{18}O emission and its relation to H_2^{16}O masers.

Contribution

The paper introduces new collisional rate data into maser simulations and investigates the potential for detecting H_2^{18}O emission alongside H_2^{16}O masers.

Findings

Optically thick H_2^{16}O lines at high column densities.

Inverted populations observed in specific H_2O lines.

Simultaneous H_2^{18}O and H_2^{16}O observations can refine cloud conditions.

Abstract

The collisional pumping of H_2^{16}O and H_2^{18}O masers in hot dense gas-dust clouds has been simulated numerically. New data on the rate coefficients for collisional transitions from Faure et al. (2007) were used in the calculations. The possibility of detecting H_2^{18}O emission in 22.2-GHz H_2^{16}O maser sources is investigated. The medium is shown to become optically thick in the H_2^{16}O lines for which an inverted level population is observed at H_2O column densities of ~10^{19}-10^{20} cm^{-2}. A simultaneous observation of H_2^{18}O emission and H_2^{16}O maser emission in the same source will allow the physical conditions in the gas-dust cloud to be refined.