VLA HiObservations of Gas Stripping in the Virgo Cluster Spiral NGC 4522

We present VLA HI observations at ~20"=1.5 kpc resolution of the highlyinclined, HI-deficient Virgo cluster spiral galaxy NGC 4522, which is one ofthe clearest and nearest cases of ongoing ICM-ISM stripping. HI is abundant andspatially coincident with the stellar disk in the center, but beyond R = 3 kpcthe HI distribution in the disk is sharply truncated and the only HI isextraplanar, and all on the northwest side. The kinematics and the morphologyof the HI appear more consistent with ongoing stripping, and less consistentwith gas fall-back which may occur long after peak pressure. Much of theextraplanar gas exhibits a modest net blueshift with respect to the galaxy'sdisk rotational velocities, consistent with gas accelerated toward the meancluster velocity. The SW side of the galaxy has less HI in the disk but more HIin the halo, suggesting more effective gas removal on the side of the galaxywhich is rotating into the ICM wind. The galaxy is 3.3 degrees ~800 kpc fromM87, somewhat outside the region of strongest cluster X-ray emission. The rampressure may be significantly stronger than standard values, due to large bulkmotions and local density enhancements of the ICM gas, which may occur in adynamic, shock-filled ICM experiencing subcluster merging. The HI and H-alphadistributions are similar, implying that the star-forming molecular ISM hasbeen effectively stripped from the outer disk of the galaxy along with the HI.Comment: 39 pages, 14 figures, accepted for AJ June 2004, Version with full resolution figures available from ftp://pegasus.astro.yale.edu/pub/kenney/n4522.ps.g