The dust properties and physical conditions of the interstellar medium in the LMC massive star-forming complex N11
Résumé
We combine Spitzer and Herschel data of the star-forming region N11 in the Large Magellanic Cloud (LMC) to produce detailed maps of the dust properties in the complex and study their variations with the interstellar-medium conditions. We also compare Atacama Pathfinder EXperiment/Large APEX Bolometer Camera (APEX/LABOCA) 870 μm observations with our model predictions in order to decompose the 870 μm emission into dust and non-dust [free-free emission and CO(3-2) line] contributions. We find that in N11, the 870 μm can be fully accounted for by these three components. The dust surface density map of N11 is combined with H I and CO observations to study local variations in the gas-to-dust mass ratios. Our analysis leads to values lower than those expected from the LMC low-metallicity as well as to a decrease of the gas-to-dust mass ratio with the dust surface density. We explore potential hypotheses that could explain the low `observed' gas-to-dust mass ratios (variations in the XCO factor, presence of CO-dark gas or of optically thick H I or variations in the dust abundance in the dense regions). We finally decompose the local spectral energy distributions (SEDs) using a principal component analysis (I.e. with no a priori assumption on the dust composition in the complex). Our results lead to a promising decomposition of the local SEDs in various dust components (hot, warm, cold) coherent with that expected for the region. Further analysis on a larger sample of galaxies will follow in order to understand how unique this decomposition is or how it evolves from one environment to another.
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