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 H awaii 2.2 m telescope was used to map the H alpha and [O III] lambda 5007 e mission-line profiles across the entire disk of the edge-on Sb galaxy NGC 4 388. We confirm a rich complex of highly ionized gas that extends similar t o 4 kpc above the disk of this galaxy. Low-ionization gas associated with s tar formation is also present in the disk. Evidence for bar streaming is de tected in the disk component and is discussed in a companion paper. Nonrota tional blueshifted velocities of 50-250 km s(-1) are measured in the extrap lanar gas northeast of the nucleus. The brighter features in this complex t end to have more blueshifted velocities. A redshifted cloud is also detecte d 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 numbe r M approximate to 3) motion of this galaxy through the ICM of the Virgo cl uster. We argue that this is because the galaxy and the high-\z\ gas lie be hind 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 ex erts insufficient ram pressure on the extraplanar gas to perturb its kinema tics. We consider several explanations of the velocity held of the extrapla nar gas. Velocities, especially blueshifted velocities on the north of the galaxy, are best explained as a bipolar outftow that is tilted by >12 degre es 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 b y density gradients in the halo gas. Velocity substructure in the outflowin g gas also suggests an interaction with ambient halo gas.