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; 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(-2) in H alpha, which corresponds to ( 0. 5-4); 10(-17) ergs s(-1) cm (-2) arcsec(-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.