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 bifurcate .
The tidal bridge has a ( B-I ) color bluer than that of NGC 6845 A inner disk .
Five strong condensations , identified 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 joint the disk of NGC 6845 A .
Since the age of the H ii regions is 3-8 Myr , star formation has been occurring along the tidal bridge and in the tidal arm well after they had begun to be torn apart ( \geq 100 Myr ) .
Satoh model fitting to the optical rotation curve of the A component reveals a kinematical mass of 4.4 ( \pm 1.2 ) 10 ^ { 11 } M \odot , inside the central 12 kpc ( H _ { 0 } = 75 { { km s ^ { -1 } Mpc ^ { -1 } } } ) .
The H i emission consist of two components , a more massive one that belongs to NGC 6845 A , and a second one associated to NGC 6845 B .
We do not detect gas associated to galaxies C and D. The total amount of H i is 1.4 \times 10 ^ { 10 } M \odot , five time higher than the H i content of the Milky Way .
The HI kinematics indicates an amount of dark matter associated to the A component two times higher than the mass inside its central 12 kpc .
The group kinematics indicates an { M / L } \approx 43 ( \pm 2 ) { ( M / L ) } _ { \odot } or { M / L } \approx 66 ( \pm 2 ) { ( M / L ) } _ { \odot } , according to two different prescriptions for the internal absorption correction .
In spite of this large difference , both values furnish similar group mass ( \approx 1 \times 10 ^ { 13 } { M _ { \odot } } ) .
Although preliminary results on N-Body simulations indicate that either B or C might well create a tidal feature like the bridge of the A component , the collision with B appears to be more favourable .