The Virgo High-Resolution CO Survey: III. NGC 4254

We present high-angular-resolution (1".5 - 5") interferometer observations ofthe \co emission in the central region of the SA(s)c galaxy NGC 4254. Theobservations were obtained using the Nobeyama Millimeter-wave Array (NMA)during the course of a long-term CO line survey of Virgo spirals. We presentthe spectra, channel maps, integrated intensity distributions, velocity fields,position--velocity diagrams, and compare the data with various optical images.The rotation velocity is already finite at the nucleus, or at least it risessteeply to 80 km/s within the central 1", indicating the existence of a massivecore of 10^8 Msun within 1" (80 pc) radius. The CO intensity maps show that theinner disk has well-developed multiple spiral arms, winding out from abar-shaped elongated molecular complex. In addition to the bisymmetric spiralarms, an asymmetric tightly wound arm with high molecular gas density is foundto wind out from the molecular bar. The molecular spiral arms, particularly thetightly wound arm, well traces optical dark lanes, and are associated withH$\alpha$ arms having many H {\sc ii} regions. The inner asymmetric spiralstructures can be explained by ram-pressure distortion of inter-arm low densityregions of the inner disk by the intra-cluster gas wind, and is indeedreproduced by a hydrodynamical simulation.