A WARM MOLECULAR HYDROGEN TAIL DUE TO RAM-PRESSURE STRIPPING OF A CLUSTER GALAXY

We have discovered a remarkable warm (130-160 K) molecular hydrogen tail with a H(2) mass of approximately 4 x 10(7) M(circle dot) extending 20 kpc from a cluster spiral galaxy, ESO 137-001, in Abell 3627. At least half of this gas is lost permanently to the intracluster medium, as the tail extends beyond the tidal radius of the galaxy. We also detect a hot (400-550 K) component in the tail that is approximately 1% of the mass. The large H(2) line to IR continuum luminosity ratio in the tail indicates that star formation is not a major excitation source and that the gas is possibly shock-heated. This discovery confirms that the galaxy is currently undergoing ram-pressure stripping, as also indicated by its previously discovered X-ray and H alpha tails. We estimate that the galaxy is losing its warm H(2) gas at a rate of similar to 2-3 M(circle dot) yr(-1). The true mass-loss rate is likely higher if we account for cold molecular gas and atomic gas. We predict that the galaxy will lose most of its gas in a single pass through the core and place a strong upper limit on the ram-pressure timescale of 1 Gyr. We also study the star-forming properties of the galaxy and its tail. We identify most of the previously discovered external H alpha sources within the tail in our 8 mu m data but not in our 3.6 mu m data; IRS spectroscopy of the region containing these H alpha sources also reveals aromatic features typically associated with star formation. From the positions of these H II regions, it appears that star formation is not occurring throughout the molecular hydrogen tail but only immediately downstream of the galaxy. Some of these H II regions lie outside the tidal radius of the galaxy, indicating that ram-pressure stripping can be a source of intracluster stars.