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Session 116 - Galaxy Clusters & Evolution.
Oral session, Saturday, January 10
Lincoln,
Optical broadband and H\alpha images from the WIYN telescope of the highly inclined Virgo cluster spiral galaxy NGC 4522 reveal a relatively undisturbed stellar disk and a peculiar distribution of H\alpha emission. Disk HII regions are relatively bright within 0.25R_25, but absent beyond 0.35R_25. Ten percent of the total H\alpha emission appears to be located above the disk plane, predominantly organized into filaments which extend from the outer edge of the truncated gas disk, on only one side of the disk. This U-shaped H\alpha morphology is reminiscent of a bow shock, and strongly suggests that the interstellar medium (ISM) of NGC 4522 is being stripped by the gas pressure of the intracluster medium (ICM). We propose that this galaxy is undergoing a strong ICM-ISM stripping event, and is one of the best nearby candidates for stripping in action.
The galaxy has a line-of-sight velocity of \simeq1200 kms^-1 with respect to the mean Virgo cluster velocity, and thus is expected to experience a strong interaction with the intracluster gas. The existence of HII regions apparently located above the disk plane suggests that star formation is occuring in the stripped gas, and that newly formed stars will enter the galaxy halo and/or intracluster space. The absence of HII regions in the disk beyond 0.35R_25, and the existence of HII regions in the stripped gas suggest that even molecular gas has been removed from the disk of the galaxy.
