Molecular and Atomic Gas in the Large Magellanic Cloud II. Three-dimensional Correlation between CO and HI

TL;DR

This study investigates the three-dimensional relationship between CO and HI gas in the Large Magellanic Cloud, revealing how HI envelopes relate to GMCs and star formation, and suggesting GMC growth via HI accretion.

Contribution

It provides new insights into the physical connection and accretion processes between HI gas and GMCs in the LMC, including the role of HI envelopes in GMC evolution.

Findings

GMCs are associated with HI envelopes

CO intensity correlates with HI intensity raised to 1.1

HI intensity increases with star formation activity in GMCs

Abstract

We compare the CO J =(1-0) and HI emission in the Large Magellanic Cloud (LMC) in three dimensions, i.e. including a velocity axis in addition to the two spatial axes, with the aim of elucidating the physical connection between giant molecular clouds (GMCs) and their surrounding HI gas. The CO J =1-0 dataset is from the second NANTEN CO survey and the HI dataset is from the merged Australia Telescope Compact Array (ATCA) and Parkes Telescope surveys. The major findings of our analysis are: 1) GMCs are associated with an envelope of HI emission, 2) in GMCs [average CO intensity] is proportional to [average HI intensity]^[1.1+-0.1] and 3) the HI intensity tends to increase with the star formation activity within GMCs, from Type I to Type III. An analysis of the HI envelopes associated with GMCs shows that their average linewidth is 14 km s-1 and the mean density in the envelope is 10 cm-3. We argue that the HI envelopes are gravitationally bound by GMCs. These findings are consistent with a continual increase in the mass of GMCs via HI accretion at an accretion rate of 0.05 Msun/yr over a time scale of 10 Myr. The growth of GMCs is terminated via dissipative ionization and/or stellar-wind disruption in the final stage of GMC evolution.