The Search for Shock-Excited H₂in Virgo Spirals Experiencing Ram Pressure Stripping

We investigate the presence of shock-excited H 2 in four Virgo cluster galaxies that show clear evidence of ongoing ram pressure stripping. Mid-infrared spectral mapping of the rotational H 2 emission lines were performed using the Infrared Spectrograph on board the Spitzer Space Telescope . We target four regions along the leading side of galaxies where the intracluster medium appears to be pushing back the individual galaxy's interstellar medium. For comparison purposes, we also study two regions on the trailing side of these galaxies: a region within an edge-on disk and an extraplanar star-forming region. We find a factor of 2.6 excess of warm H 2 /PAH in our sample relative to the observed fractions in other nearby galaxies. We attribute the H 2 /PAH excess to contributions of shock-excited H 2 which is likely to have been triggered by ongoing ram pressure interaction in our sample galaxies. Ram pressure driven shocks may also be responsible for the elevated ratios of [Fe ii ]/[Ne ii ] found in our sample.