Hα tail, intracluster HII regions, and star formation:: ESO 137-001 in Abell 3627

We present the discovery of a 40 kpc H alpha tail and at least 29 emission-line objects downstream of a star-forming galaxy, ESO 137-001, in the rich, nearby cluster A3627. The galaxy is known to possess a dramatic 70 kpc X-ray tail. The detected H alpha tail coincides positionally with the X-ray tail. The H alpha emission in the galaxy is sharply truncated on the front and the sides near the nucleus, indicating significant ram pressure stripping. ESO 137-001 is thus the first cluster late-type galaxy known unambiguously to have both an X-ray tail and an H alpha tail. The emission-line objects are all distributed downstream of the galaxy, with projected distances of up to 39 kpc from the galaxy. From the analysis on the H alpha(off) frame and the estimate of the background emission-line objects, we conclude that it is very likely that all 29 emission-line objects are H II regions in A3627. The high surface number density and luminosities of these H II regions (up to 1040 ergs s(-1)) dwarf the previously known examples of isolated H II regions in clusters. We suggest that star formation may proceed in the stripped ISM in both the galactic halo and intracluster space. The total mass of formed stars in the stripped ISM of ESO 137-001 may approach several times 107 M-circle dot. Therefore, stripping of the ISM not only contributes to the ICM, but also adds to the intracluster stellar light through subsequent star formation. The data also imply that ESO 137-001 is in an active stage of transformation accompanied by the buildup of a central bulge and depletion of the ISM.