Environmental effects on gaseous disks of the Virgo spiral galaxies

We found high molecular fractions (f(mol); ratio of the molecular to total gas surface densities) in three of five Virgo spiral galaxies in spite of their low total gas column density, based on (CO)-C-12 J = 1-0 observations with the Nobeyama 45 m telescope equipped with a multibeam receiver, BEARS. We interpret this as a result of environmental effects. Combining the CO data with H I data, the relationship between the surface density of the total gas (H I plus H-2) and fmol indicates that the three galaxies near the cluster center have larger fmol values than expected for field galaxies, while the others show normal fmol. The large fmol is interpreted as being due either to effective H I gas stripping, even in the inner disks, or to large ISM pressure induced by the high ICM pressure and/or ram pressure, although the possibility of an unusually high metallicity cannot be ruled out.