The remarkable 60 x 2 kpc optical filament associated with a poststarburst galaxy in the Coma Cluster

In the deep narrowband image of the Coma Cluster taken with Suprime-Cam of the Subaru Telescope, we found an extremely long and narrow (-60 x 2 kpc) H alpha -emitting region associated with a poststarburst galaxy (D100). Follow-up spectroscopy shows that the region has the same redshift as D100. The surface brightness of the region is typically 25 mag (AB) arcsec super(-2) in H alpha , which corresponds to (0.5-4) x 10 super(-17) ergs s super(-1) cm super(-2) arcsec super(-2). We propose two possible explanations for the origin of the region; gas stripped off from a merged dwarf or gas stripped off from D100 by ram pressure. Either scenario meets with difficulty in fully explaining all the observed characteristics of the region.