A Warm Molecular Hydrogen Tail Due to Ram Pressure Stripping of a Cluster Galaxy

摘要

We have discovered a remarkable warm (130-160 K) molecular hydrogen tail witha H_2 mass of approximately 4*10^7 solar masses extending 20 kpc from a clusterspiral galaxy, ESO 137-001, in Abell 3627. At least half of this gas is lostpermanently to the intracluster medium, as the tail extends beyond the tidalradius of the galaxy. We also detect a hot (400-550 K) component in the tailthat is approximately 1% of the mass. The large H_2 line to IR continuumluminosity ratio in the tail indicates that star formation is not a majorexcitation source and that the gas is possibly shock-heated. This discoveryconfirms that the galaxy is currently undergoing ram-pressure stripping, asalso indicated by its X-ray and Halpha tails found previously. We estimate thegalaxy is losing its warm H_2 gas at a rate of ~ 2-3 solar masses per year. Thetrue mass loss rate is likely higher if we account for cold molecular gas andatomic gas. We predict that the galaxy will lose most of its gas in a singlepass through the core and place a strong upper limit on the ram-pressuretimescale of 1 Gyr. We also study the star-forming properties of the galaxy andits tail. We identify most of the previously discovered external Halpha sourceswithin the tail in our 8 um data but not in our 3.6 um data; IRS spectroscopyof the region containing these Halpha sources also reveals aromatic featurestypically associated with star formation. From the positions of these HIIregions, it appears that star formation is not occurring throughout themolecular hydrogen tail but only immediately downstream of the galaxy. Some ofthese HII regions lie outside the tidal radius of the galaxy, indicating thatram-pressure stripping can be a source of intracluster stars.