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

TL;DR

This study measures the $^{13}$CO (2-1) to $^{12}$CO (2-1) line ratio in 100 GMCs in the LMC, revealing correlations with star formation activity and internal cloud conditions.

Contribution

It provides the first large sample analysis of the line ratio in the LMC and links it to star formation indicators like YSOs.

Findings

Median line ratio of 0.078 with most between 0.058 and 0.107.

Nearly linear relationship between line luminosity and ratio.

Clouds with IR-bright YSOs have higher $^{13}$CO emission.

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.