2001AJ....122..140W

We present high-resolution H I 21 cm line, 20 cm radio continuum, and CO (1-0) line observations of the luminous infrared galaxy pair NGC 6670. NGC 6670 consists of two edge-on disk galaxies (NGC 6670E and NGC 6670W) with a projected nuclear separation of ∼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 far-infrared-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_H2, 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_☉/M_☉, 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_H2>10 L_☉/M_☉). Other indicators of starburst activity, such as CO brightness temperature and infrared surface brightness, are also observed.