Ongoing gas stripping in the Virgo Cluster spiral galaxy NGC 4522

The Virgo Cluster galaxy NGC 4522 is one of the best spiral candidates for intracluster medium-interstellar medium (ICM-ISM) stripping in action. Opti cal broadband and H alpha images from the WIYN telescope of the highly incl ined galaxy reveal a relatively undisturbed stellar disk and a peculiar dis tribution of H alpha emission. Ten percent of the H alpha emission arises f rom extraplanar H II regions which appear to lie within filamentary structu res greater than or equal to 3 kpc long above one side of the disk. The fil aments emerge from the outer edge of a disk of bright H alpha emission whic h is abruptly truncated beyond 0.35R(25). Together the truncated H alpha di sk and extraplanar H alpha filaments are reminiscent of a bow shock morphol ogy, which strongly suggests that ISM of NGC 4522 is being stripped by the gas pressure of the ICM. The galaxy has a line-of-sight velocity of similar or equal to 1300 km s(-1) with respect to the mean Virgo Cluster velocity and thus is expected to experience a strong interaction with the intraclust er gas. The existence of H II regions apparently located above the disk pla ne suggests that star formation is occurring in the stripped gas, and that newly formed stars will enter the galaxy halo and/or intracluster space. Th e absence of H II regions in the disk beyond 0.35R(25) and the existence of H II regions in the stripped gas suggest that even molecular gas has been effectively removed from the disk of the galaxy.