We present a review of spatially resolved giant molecular clouds (GMCs) in nearby galaxies, aiming at providing a template of GMC properties, which may be extrapolated to distant galaxies. We focus on the Magellanic system including the Large and Small Magellanic Clouds (LMC, SMC), M33, and a few dwarfs as observed in the = 1–0 12CO transition at 2.6-mm wavelength. The X factor, a conversion factor of the 12CO intensity to total molecular column density, and the GMC mass distribution, /, are similar among these galaxies, suggesting that GMCs share similar properties in the Local Group. The GMCs are classified into three types according to their level of star-formation activity and the types are interpreted in terms of evolution in 20–30 Myr rather than as three different generic types. A three-dimensional comparison including the velocity axis has revealed that GMCs in the LMC are associated with H envelopes. The H envelopes are probably gravitationally bound and may be infalling to increase the GMC mass via H-H conversion. Recent submillimeter observations are revealing dense and warm clumps in GMCs, suggesting that the interior of a GMC also follows contraction leading to star formation on a similar timescale. Finally, we present an attempt to place these GMC properties among more distant galaxies and discuss future observational prospects.


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  • Article Type: Review Article
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