Study of the Interacting System Ngc 6845 Irapuan Rodrigues1,2 and Horacio Dottori2

We present optical spectroscopy, B, V , R, and I CCD photometry, and VLA neutral hydrogen observations of the interacting quartet NGC 6845, also know as Klemola 30. NGC 6845 A, the dominant component, sports a broad and bright tidal bridge and a faint tidal tail, which bifurcates. The tidal bridge has a B[I color bluer than that of the inner disk of NGC 6845 A. Five strong condensations, identiÐed as H II regions brighter than the brightest one known in our Galaxy, are found along the tidal bridge, with the two most luminous located at the bridge tip. Two giant H II regions, comparable to 30 Dor, are located where the tidal bridge and the tidal tail join the disk of NGC 6845 A. Since the age of the H II regions is 3È8 Myr, star formation continued to occur along the tidal bridge and in the tidal arm well after they began to be torn apart (o100 Myr). Satoh model Ðtting to the optical rotation curve of the A component reveals a kinematical mass of (4.4^ 1.2)] 1011 inside the central 12 kpc M _ , km s~1 Mpc~1). The H I emission consist of two components, a more massive one that (H0\ 75 belongs to NGC 6845 A and a second one associated with NGC 6845 B. We do not detect gas associated with galaxies C and D. The total amount of H I is 1.4] 1010 5 time higher than the H I M _ , content of the Milky Way. The H I kinematics indicates an amount of dark matter associated with the A component 2 times higher than the mass inside its central 12 kpc. The group kinematics indicates or according to two di†erent prescriptions for the internal M/L B 43(^2)(M/L ) _ M/L B 66(^2)(M/L ) _ , absorption correction. In spite of this large di†erence, both values furnish a similar group mass (B1 ] 1013 Although preliminary results on N-body simulations indicate that either B or C might M _ ). well create a tidal feature like the bridge of the A component, the collision with B appears to be more favorable.