The Nature of the Peculiar Virgo Cluster Galaxies NGC 4064 and NGC 4424

We present a detailed study of the peculiar HI-deficient Virgo cluster spiralgalaxies NGC 4064 and NGC 4424, using $^{12}$CO 1-0 interferometry, opticalimaging and integral-field spectroscopic observations, in order to learn whattype of environmental interactions have afected these galaxies. Optical imagingreveals that NGC 4424 has a strongly disturbed stellar disk, with banana-shapedisophotes and shells. NGC 4064, which lies in the cluster outskirts, possessesa relatively undisturbed outer stellar disk and a central bar. In both galaxiesH-alpha emission is confined to the central kiloparsec. CO observations revealbilobal molecular gas morphologies, with H-alpha emission peaking inside the COlobes, implying a time sequence in the star formation process.Gas kinematicsreveals strong bar-like non-circular motions in the molecular gas in bothgalaxies, suggesting that the material is radially infalling. In NGC 4064 thestellar kinematics reveal strong bar-like non-circular motions in the central 1kpc. On the other hand, NGC 4424 has extremely modest stellar rotationvelocities (Vmax ~ 30 km s-1), and stars are supported by random motions as farout as we can measure it. The observations suggest that the peculiarities ofNGC 4424 are the result of an intermediate-mass merger plus ram pressurestripping. In the case of NGC 4064, the evidence suggests an already stripped"truncated/normal" galaxy that recently suffered a minor merger or tidalinteraction with another galaxy. We propose that galaxies with"truncated/compact" H-alpha morphologies such as these are the result of theindependent effects of ram pressure stripping, which removes gas from the outerdisk, and gravitational interactions such as mergers, which heat stellar disks,drive gas to the central kpc and increase the central mass concentrations.Comment: 42 pages, 21 figure