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The formation of molecular clouds out of HI gas is the first step toward starformation. Its metallicity dependence plays a key role to determine starformation through the cosmic history. Previous theoretical studies withdetailed chemical networks calculate thermal equilibrium states and/or thermalevolution under one-zone collapsing background. The molecular cloud formationin reality, however, involves supersonic flows, and thus resolving the cloudinternal turbulence/density structure in three dimension is still essential. Wehere perform magnetohydrodynamics simulations of 20 km s^-1 converging flows ofWarm Neutral Medium (WNM) with 1 micro Gauss mean magnetic field in themetallicity range from the Solar (1.0 Zsun) to 0.2 Zsun environment. The ColdNeutral Medium (CNM) clumps form faster with higher metallicity due to moreefficient cooling. Meanwhile, their mass functions commonly follow dn/dmproportional to m^-1.7 at three cooling times regardless of the metallicity.Their total turbulence power also commonly shows the Kolmogorov spectrum withits 80 percent in the solenoidal mode, while the CNM volume alone indicates thetransition towards the Larson's law. These similarities measured at the sametime in the unit of the cooling time suggest that the molecular cloud formationdirectly from the WNM alone requires a longer physical time in a lowermetallicity environment in the 1.0--0.2 Zsun range. To explain the rapidformation of molecular clouds and subsequent massive star formation possiblywithin less than 10 Myr as observed in the Large/Small Magellanic Clouds(LMC/SMC), the HI gas already contains CNM volume instead of pure WNM.

Metallicity Dependence of Molecular Cloud Hierarchical Structure at Early Evolutionary Stages