STRANGE FILAMENTARY STRUCTURES (FIREBALLS) AROUND A MERGER GALAXY IN THE COMA CLUSTER OF GALAXIES

We found an unusual complex of narrow blue filaments, bright blue knots, and H alpha -emitting filaments and clouds, which morphologically resembled a complex of "fireballs," extending up to 80 kpc south from an E+A galaxy RB 199 in the Coma Cluster. The galaxy has a highly disturbed morphology indicative of a galaxy-galaxy merger remnant. The narrow blue filaments extend in straight shapes toward the south from the galaxy, and several bright blue knots are located at the southern ends of the filaments. The [image] band absolute magnitudes, half-light radii, and estimated masses of the bright knots are [image]-12 to -13 mag, [image]200-300 pc, and [image]10 super(6)-10 super(7) M[image], respectively. Long, narrow H alpha -emitting filaments are connected at the south edge of the knots. The average color of the fireballs is [image], which is bluer than RB 199, suggesting that most of the stars in the fireballs were formed within several times [image] yr. The narrow blue filaments exhibit almost no H alpha emission. Strong H alpha and UV emission appear in the bright knots. These characteristics indicate that star formation recently ceased in the blue filaments and now continues in the bright knots. The gas stripped by some mechanism from the disk of RB 199 may be traveling in intergalactic space, forming stars left along its trajectory. The most plausible fireball formation mechanism is ram pressure stripping by high-speed collision between the galaxy and the hot intracluster medium. The fireballs may be a snapshot of diffuse intracluster population formation, or halo star population formation in a cluster galaxy.