We investigate the physical properties of molecular hydrogen (H2) in isolatedand interacting disk galaxies with different masses and Hubble types by usingchemodynamical simulations with H2 formation on dust grains and dust growth anddestruction in interstellar medium (ISM). We particularly focus on thedependences of H2 gas mass fractions (f_H2), spatial distributions of HI andH2, and local H2-scaling relations on initial halo masses (M_h), baryonicfractions (f_bary), gas mass fractions (f_g), and Hubble types. The principalresults are as follows. The final f_H2 can be larger in disk galaxies withhigher M_h, f_bary, and f_g. Some low-mass disk models with M_h smaller than10^10 M_sun show extremely low f_H2 and thus no/little star formation, even ifinitial f_g is quite large (>0.9). Big galactic bulges can severely suppressthe formation of H2 from HI on dust grains whereas strong stellar bars can notonly enhance f_H2 but also be responsible for the formation of H2-dominatedcentral rings. The projected radial distributions of H2 are significantly morecompact than those of HI and the simulated radial profiles of H2-to-HI-ratios(R_mol) follow roughly R^-1.5 in MW-type disk models. Galaxy interaction cansignificantly increase f_H2 and total H2 mass in disk galaxies. The localsurface mass densities of H2 can be correlated with those of dust in a galaxy.The observed correlation between R_mol and gas pressure (R_mol ~ P_g^0.92) canbe well reproduced in the simulated disk galaxies.
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