The ${}^{13}\mathrm{CO}(2{-}1)/^{12}\mathrm{CO}(2{-}1)$ Line Ratio from 100 Molecular Clouds in the Large Magellanic Cloud

Abstract

We analyze the line ratio of the $^{13}$CO (2-1) to $^{12}$CO (2-1) rotational transitions observed from new ALMA observations of 100 Giant Molecular Clouds (GMCs) that span the Large Magellanic Cloud. We measure a median line ratio of $^{13}\mathrm{CO}(2{-}1)/^{12}\mathrm{CO}(2{-}1) = 0.078$ with $68\%$ of the sample falling between 0.058 and 0.107. A regression analysis confirms a nearly linear relationship across two orders of magnitude in line luminosity. Moreover, we find that the inclusion of $(L_{\text{FIR}})$ from Young Stellar Objects as a predictor variable of the line ratio significantly improves the quality of the fit, with clouds hosting IR-bright YSOs having relatively brighter $^{13}$CO emission. This analysis indicates that active star forming molecular clouds have different internal conditions than more quiescent clouds.