We present high resolution H i 21 cm line , 20 cm radio continuum , and CO ( 1–0 ) line observations of the luminous infrared galaxy NGC 6670 .
NGC 6670 consists of two edge-on disk galaxies ( NGC 6670E and NGC 6670W ) with a projected nuclear separation of \sim 16 kpc .
While there are no optically identified tidal features and the molecular disks are not distorted much , we have detected a 90 kpc long H i tail which suggests that the galaxies are interacting and have already experienced at least one close encounter .
The galaxies appear to be gravitationally bound and in a prograde-prograde orbit , which is the most efficient for producing tidal tails .
Our observations suggest that the H i at larger galactic radii has been ejected to form the tails and the remnant H i disks have been perturbed by the interaction .
In particular , we find that the H i disk of NGC 6670E appears to have been nearly destroyed .
We conclude that the previous encounter between the galaxies had a large impact parameter and that the system is still in an early stage of interaction .

Even though NGC 6670 is in an early stage of interaction , we find that there is evidence for nuclear starbursts already present .
The CO ( 1–0 ) observations show large molecular gas reservoirs in the central regions and the 20 cm radio continuum observations reveal enhanced star formation activity in the nuclear regions of both galaxies .
The spatial extent of the 20 cm emission and the FIR-radio correlation further rule out active galactic nuclei as the source of the IR luminosity from NGC 6670 .
We estimate the ratio L _ { IR } / M _ { H _ { 2 } } , which is often used as an indicator of star formation efficiency , in the nuclear regions of NGC 6670E and NGC 6670W to be 18 and 11 L _ { \sun } / M _ { \sun } , respectively .
The nuclear star formation efficiency of these two galaxies has been elevated to the level observed in other nearby starburst galaxies ( L _ { IR } / M _ { H _ { 2 } } > 10 L _ { \sun } / M _ { \sun } ) .
Other indicators of starburst activity such as CO brightness temperature and infrared surface brightness are also observed .