Galactic-scale outflow and supersonic ram-pressure stripping in the Virgo cluster galaxy NGC 4388

The Hawaii Imaging Fabry-Perot Interferometer (HIFI) on the University of Hawaii 2.2 m telescope was used to map the H alpha and [O III] lambda 5007 emission-line profiles across the entire disk of the edge-on Sb galaxy NGC 4388. We confirm a rich complex of highly ionized gas that extends similar to 4 kpc above the disk of this galaxy. Low-ionization gas associated with star formation is also present in the disk. Evidence for bar streaming is detected in the disk component and is discussed in a companion paper. Nonrotational blueshifted velocities of 50-250 km s(-1) are measured in the extraplanar gas northeast of the nucleus. The brighter features in this complex tend to have more blueshifted velocities. A redshifted cloud is also detected 2 kpc southwest of the nucleus. The velocity held of the extraplanar gas of NGC 4388 appears to be unaffected by the inferred supersonic (Mach number M approximate to 3) motion of this galaxy through the ICM of the Virgo cluster. We argue that this is because the galaxy and the high-\z\ gas lie behind a Mach cone with opening angle similar to 80 degrees. The shocked ICM that flows near the galaxy has a velocity of similar to 500 km s(-1) and exerts insufficient ram pressure on the extraplanar gas to perturb its kinematics. We consider several explanations of the velocity held of the extraplanar gas. Velocities, especially blueshifted velocities on the north of the galaxy, are best explained as a bipolar outftow that is tilted by >12 degrees from the normal to the disk. The observed offset between the extraplanar gas and the radio structure may be due to buoyancy or refractive bending by density gradients in the halo gas. Velocity substructure in the outflowing gas also suggests an interaction with ambient halo gas.